The Ontogeny of Kin Recognition in Two Species of Ground Squirrels 1

Transcription

1 AMER. ZOOL., 22: (1982) The Ontogeny of Kin Recognition in Two Species of Ground Squirrels 1 WARREN G. HOLMES Department of Psychology, University of Michigan, Ann Arbor, Michigan AND PAUL W. SHERMAN Section of Neurobiology and Behavior, Cornell University, Ithaca, New York SYNOPSIS. We report results of a three year comparative laboratory study of kin recognition abilities in Arctic ground squirrels (Spermophilus parryii) and Belding's ground squirrels (S. beldingi), and a field investigation of kin recognition in S. beldingi. Our laboratory work shows that in both species, preweaned pups reared together, whether they are biological siblings or cross-fostered (unrelated) nestmates, are equally aggressive in subsequent paired arena tests. Thus, pups that share a natal nest are treated like siblings. Among pups reared apart, sister-sister pairs are less aggressive in arena tests than are pairs of nonkin females, whereas relatedness does not affect male-male or male-female aggression. Thus both relatedness and rearing environment mediate recognition among female S. parryii and S. beldingi. In free-living Belding's ground squirrels at Tioga Pass, California, dam-offspring and sister-sister recognition apparently first occur at weaning, coincident with aboveground emergence of juveniles. Most intriguing (electrophoretically identified) littermate full-sisters and maternal half-sisters, which result from multiple mating by females, seem to treat each other differently despite having shared a natal nest. The full-sisters are less agonistic and more cooperative than the half-sisters. In interpreting these laboratory and field results, we explore four proximal mechanisms by which kin might be identified, including one in which recognition is based on (learned) phenotypic similarity to an individual's nestmates or itself (phenotype matching). Our data and those of several recent investigators of recognition in other taxa implicate both association with relatives and phenotype matching in the ontogeny of kin recognition. INTRODUCTION ing {e.g., Hoogland, 1982) imply that A refinement of Darwin's theory of evo- mechanisms exist whereby relatives can be lution by natural selection has focused at- identified. Glven tendon on one type of conspecific discrim- the enthusiastic response to Hamination: kin recognition. This theoretical llton ' s ldeas > the kin recognition literature refinement is W. D. Hamilton's "inclusive ls surprisingly meager. Various studies have fitness" hypothesis (1964, 1972), which touched on kin recognition, but detailed predicts that genetic relatedness will be an investigations are rare and limited to a few important variable in the evolution of so- categories of kinship. Mechanisms of parcial behavior. Hamilton's hypothesis has ent-offspnng identification (usually mothrecently received considerable empirical er-offspring) have been investigated in Wlstar rats and theoretical support (reviewed by Wil- ( Rattus norvegicus by Leon, son, 1975; Alcock, 1979; Alexander, 1979; 1978 )> domestic goats (Capra htrcus; Gub- Markl, 1980; Barash, 1982). The wide- ernick, 1980), Richardson's ground squirspread occurrence of nepotism (favoritism rels (Spermophilus nchardsonu; Michener, shown kin) and the rarity of close inbreed- ' 9? 4)> squirrel monkeys (Saimin scmreus; Kaplan^ al., 1977), bank swallows (Ripana riparia; Hoogland and Sherman, 1976;..., c. _,,..,,. Beecher el al., 1981a, b), several gulls (La- 1 rrom the symposium on rrom Individual to bpecies.,, i r»4rv\ Recognition: Theories and Mechanisms presented at the "" S PP- reviewed by Beer, 1970), terns Annual Meeting of the American Society of Zoolo- {Sterna spp.; Davies and Camck, 1962; gists, December 1980, at Seattle, Washington. Buckley and Buckley, 1972), and cichlid 491

2 492 W. G. HOLMES AND P. W. SHERMAN fishes (Hemichromis and Cichlasoma spp.; Myrberg, 1966; Barnett, 1977a, b, 1982). Mechanisms of sibling recognition have been studied in sweat bees (Lasioglossum zephyrum; Kukuk et al., 1977; Greenberg, 1979; Buckle and Greenberg, 1981), tadpoles of American toads {Bufo americanns; Waldman and Adler, 1979; Waldman, 1981, 1982) and Cascade frogs (Rana cascadae; Blaustein and O'Hara, 1981, 1982; O'Hara and Blaustein, 1981), spiny mice (Acomys cahirinus; Porter et al., 1978, 1981; Porter and Wyrick, 1979), Richardson's ground squirrels (Sheppard and Yoshida, 1971; L. Davis, personal communication), deer mice (Peromyscus leucopus; Grau, 1982), and pigtail macaques (Macaca nemestrina; Wu et al., 1980). Here we report results of a 3-yr comparative study of the ontogeny and specificity of (1) sibling-sibling recognition in Arctic ground squirrels (Spermophilus parryii) and Belding's ground squirrels (S. beldingi) in the laboratory, and (2) damoffspring and sib-sib recognition in Belding's ground squirrels in the field. We chose these species for several reasons. In the field, females of both S. parryii and S. beldingi live near various maternal relatives. Closely related female kin cooperate, whereas nonkin do not; in other words, discriminative nepotism is important in the social behavior of both. Although there are many similarities in the ecology and behavior of these two sciurids, there are also differences that provide the basis for a comparative study. Finally, adults and juveniles of both species can be maintained in the laboratory, and their abilities to discriminate among conspecifics can be assessed there. Our investigation proceeded on two fronts. First, W. G. Holmes live-trapped pregnant females of both species and brought them to his laboratory. Within 3 hr of birth, young were intraspecifically cross-fostered. Juvenile S. parryii and yearling S. beldingi pairs were observed in an arena to see how their behavior was affected by (1) association during rearing, and (2) genetic relatedness. Second, P. VV. Sherman investigated S. beldingi kin recognition in the field. He transferred pups born in captivity into field nest burrows when the young were at various developmental stages. By scoring acceptance rates and observing the behavior of transferred young as yearlings, he investigated the ontogeny of dam-offspring and sibling recognition. He also compared the behavior of asymmetrically related female littermates: electrophoretically identified fullsisters (same dam and sire) and half-sisters (same dam only), which result from female polygamy. When taken together, our results suggest that both relatedness and rearing conditions affect the development of kin recognition in these two species in the laboratory, and also in free-living Belding's ground squirrels. BIOLOGY OF THE STUDY ANIMALS Belding's ground squirrels are diurnal, social rodents that inhabit subalpine meadows in the far western United States (Turner, 1972). For the last 13 summers ( ), M. L. Morton, P. W. Sherman, and their students have studied a population of these animals at the summit of Tioga Pass, California, in the central Sierra Nevada (Morton, 1975; Morton and Sherman, 1978; Sherman, 1976, 1977, 1980a, b, 1981a, b; Sherman and Morton, 1979). Animals there are active aboveground from May through September; they hibernate the rest of the year. Females are sexually mature the summer following their birth (as "yearlings"), whereas males do not reproduce until they are two. Females surviving their first winter live an average of 2.5 yr, whereas most males surviving that winter live only 1 yr more. In the spring, males emerge 1-2 wk before females. About a week after a female emerges, she becomes sexually receptive; receptivity typically lasts only a few hours on a single afternoon, during which time each female mates multiply with several different males. Following mating, females establish territories surrounding nest burrows, which they defend against unrelated conspecifics. Females rear a single litter of three to six young per year. Because dams nest alone, pups interact only with each other and their dam until they first emerge aboveground (at weaning), when they are

3 3-4 vvk old. During their first few days above ground, juveniles (young above ground during their first summer) frequently interact with neighboring conspecifics. Nestmates continue to share their natal burrow for a few weeks after emergence, at which time dispersal begins. Natal dispersal is asymmetric by sex, with juvenile males moving considerably farther from home than their sisters. Indeed, before their first winter's hibernation, most juvenile males have dispersed several hundred meters from their natal area, never to return; their sisters, in contrast, frequently hibernate near their dam. Each year after mating, adult males emigrate again, with the most polygynous males moving farthest. Thus, males seldom, if ever, interact with their matrilineal relatives, mates, or mates' offspring. Females, in contrast, spend their lives surrounded by and interacting with female kin. Close female relatives (dam-daughter and sister pairs) seldom chase each other from territories or fight for possession of nest burrows; indeed, they cooperate to defend each others' young against infanticidal conspecifics, and give alarm calls in each others' presence. Among close female kin, cooperation increases with increasing genetic relatedness, so social favoritism among female 5. beldingi is a manifestation of nepotism. Arctic ground squirrels are also diurnal, social rodents. They inhabit meadows in arctic-alpine areas of Canada and Alaska above 60 N latitude (Hall and Kelson, 1959). Relatively little has been published about their ecology, demography, or social behavior. Here, we rely on a recently completed Ph.D. thesis (McLean, 1981), supplemented by the less detailed observations of Green (1977), Carl (1971), and Holmes (unpublished). Arctic ground squirrels are typically above ground from mid-april until early October. Adult males emerge 1-2 wk before females; mating occurs 7-10 days after a female emerges. During the 2-wk mating period (inferred from the timing of births of litters), male home ranges overlap considerably. Males that trespass into home ranges of other males during KIN RECOGNITION IN GROUND SQUIRRELS 493 females' gestation and lactation are usually attacked and chased by the resident. Females produce one litter per year (usually five or six young) and nest and nurse their young alone. Infants interact only with each other and their dam until they are days old. Just prior to juvenile emergence (weaning), dams often transport them to a new burrow system, and two or three dams sometimes place pups in the same burrow. Such dams are typically mother-daughter or sister-sister pairs, and clumping occurs selectively with close relatives rather than randomly with nearest neighbors, who are not necessarily the closest kin. Thus, young begin to interact with their aunts and (juvenile) cousins prior to or coincident with weaning, and continue to do so for several weeks postweaning. Then, as in S. beldingi, males permanently disperse while females remain in their natal area. Female Arctic ground squirrels spend their lives surrounded by near and distant female relatives. Interactions between dams and adult daughters and sister-sister pairs are usually amicable and rarely agonistic. Females more distantly related than sisters seem to be less cooperative, but not as agonistic as nonkin. In the fall of the year, the animals seek hibernacula, where they spend the winter alone. Females survive on body fat stores (as do all 5. beldingi); in addition, male S. parryii may use food that they have cached for overwinter survival. In areas where suitable hibernacula are limited, competition for the best locations has been observed; similar agonism over winter burrows has not been observed in 5. beldingi. METHODS Laboratory study animals Animals tested for recognition abilities were acquired by live-trapping field-mated, pregnant females and air freighting them to Holmes's laboratory. Females were shipped individually in 1-gal paint cans filled with straw. They arrived several days to two weeks before giving birth. In 1978, pregnant Arctic ground squirrels (n = 16) were trapped in south-central

4 494 W. G. HOLMES AND P. W. SHERMAN Alaska, near Hatcher Pass (61 N, 149 W; elev. = 1,010 m); in 1979, pregnant females (n = 18) were caught in central Alaska, about 20 km west of Paxson along the Denali Highway (63 N, 143 W; elev. = 305 m). Pregnant Belding's ground squirrels (n = 18) were trapped in 1979 on several subalpine meadows in the vicinity of Tioga Pass, California (Mono Co., 38 N, 119 W; elev. = ca. 3,000 m). For both species females were trapped far enough apart (>400 m) that their litters were probably not sired by the same male or males. Litter A i CROSS-FOSTERING DESIGN \ \ \ \ / \ /. Litter B Or? Bf b, b2 b3 / / / * / 6 * Parents of litters Litters at birth Cross-fostering between litters Laboratory rearing conditions Wild-caught females were placed in individual stainless steel cages (66 x 46 x 28 cm), which contained a straw-filled plywood nest box with an entry hole and a removable top. They were provided ad lib. access to water, rat chow (Purina), mouse breeder chow (Teklad), sunflower seeds, and lettuce. All cages were positioned on racks in a single 6.1-m 2 colony room. In 1978 only S. parryii were kept in the room; in 1979 both species were housed there. The room was maintained at about 20 C under a 14L: 10D photoperiod (lights on at 0900). Laboratory cross-fostering procedures Intraspecific cross-fostering was performed similarly for both species. First, parturition was assessed by inspecting each female's nest box several times a day. Inspections were made with particular care in the early morning (0600 to 0900) after it was discovered that most litters were born then. Within 3 hr of birth, each pup was toe-clipped for permanent identification. Sometimes parturition was observed; more often, however, the time since birth was inferred, based on the condition of the umbilical cord stub ( cm), and the amount and consistency of placental fluid adhering to the pup. Holmes found that he could estimate the time since parturition using these indicators, based on a preliminary study (1977) involving nearly continuous observations of six litters of S. parryii and three of S. beldingi from birth until they were 5-7 hr old. When two females produced litters with- 6 n 6 n o, a. on on D o,-a3 b -t>. Sibs Reared Sibs Reared Nonsibs Together Apart Reared Together (S.RT) (S.RA.) (NS.RT) Litters during "z a 4 b z b 4 rearing on b,-o4 Nonsibs Reared Apart (NS.RA.) Pairs tested Rearing X Relatedness FIG. 1. Intraspecific cross-fostering design used in our laboratory tests. The "?" indicates that dams (females = circles) were field-mated so that the sire (males = squares) of the litter was unknown. "Pairs tested" refers to each of the four groups of ground squirrels and indicates whether members of a pair were (1) uterine siblings or nonsiblings and (2) reared together or reared apart. This diagram depicts only one of several combinations of litter size, sex ratio, sex-of-pair tested, and the ratio of biological: foster siblings that were reared together. in 3 hr of each other, their pups were crossfostered to create four kinds of infant pairs (Fig. 1): (1) Siblings-Reared Together (S.RT.) uterine siblings reared together, by either their biological dam or a foster dam; (2) Siblings-Reared Apart (S.RA.) uterine siblings reared in different nest boxes, one by its biological dam and the other by a foster dam; (3) Nonsiblings- Reared Together (NS.RT.) nonsibling young reared together by the biological dam of one of them; and (4) Nonsiblings- Reared Apart (NS.RA.) nonsibling young reared in different nest boxes by their biological or foster dam. These categories describe the relatedness and rearing condition of members of a pair, but not the identity of the other animals with whom

5 each subject was reared. In fact, nearly all pups in each group were reared with at least one of their biological siblings and one nonsib. Cross-fostering was accomplished by removing the dams and litters from their cages for a standard period of 20 min, executing the appropriate switches of pups, then returning females and infants to the females' own nests. Observation of dams and reunited pups (under red light) revealed that dams readily accepted foreign pups; no differences were noted in how dams licked or handled biological versiis foster pups. Both sets of young grew at the same rate, and body weights of the two groups were indistinguishable at weaning (P>0.1, ^-tests) and later at testing (P > 0.1, for both species). In our experimental design, only two adult females were involved in a given cross-fostering (Fig. 1). If an odd number of females gave birth during a 3-hr interval, one litter was toe-clipped, handled as if being cross-fostered, and returned to its nest. These pups became members of the S.RT. group (some juveniles tested in this group also came from litters containing cross-fostered pups). In this report, "group" refers to one of the four relatedness x rearing conditions (Fig. 1). "Siblings" and "nonsiblings" indicate whether or not infants were uterine kin. Due to the frequency of multiple mating and multiple paternity in S. beldingi litters (Hanken and Sherman, 1981), whether "siblings" were full- or half-siblings was unknown in laboratory tests; due to the complete lack of information about either female polygamy or multiple paternity in S. parryii, whether uterine kin were full- or half-siblings was also unknown. Laboratory testing for recognition For both species, recognition was assessed by observing the behavior of pairs of animals in a 1-m 3 plywood arena, with a plexiglass front and an opaque dividing partition that was lifted with a rope and pulley arrangement. The arena was painted dull yellow, and its floor sealed with marine varnish. A 3 X 3 grid (i.e., 33-cm squares) was painted on the arena floor. KIN RECOGNITION IN GROUND SQUIRRELS 495 Holmes, who observed all pairs, sat 2.7 m in front of the arena, behind an opaque curtain with a viewing slit cut in it. The arena was illuminated by two white lights (100 watt). About 3 wk before testing, Holmes and his assistant marked each animal with hair dye, putting one or two spots on the shoulders, sides, or flanks. Dye marks did not reveal an individual's group of origin. Sometimes several ground squirrels shared similar marks. When subjects that were reared together were marked similarly, the assistant used toeclip numbers to identify individuals in the colony room. Holmes used size or pelage differences to identify individuals during a test if their dye marks were very similar. To begin a test, the assistant carried both members of a pair from the colony room into the test room in separate cages where each had been isolated for min. Testing order was determined by first assigning pairs within all four groups a number, and then using a random numbers table to specify consecutive tests, regardless of group. The assistant placed the two subjects on opposite sides of the arena's opaque dividing partition, then departed. Subjects remained separated 3-5 min. During this period if either subject did not move around and touch all sides of its half of the arena, the test was halted. This occurred in 8.4% of the 5. parryii tests and in 8.1% of the S. beldingi tests, distributed about equally across the four groups. After the initial familiarization period, Holmes unobtrusively lifted the partition, and the animals were allowed to interact for 5 min, beginning when (1) body contact lasting at least 1 sec occurred, or (2) when one animal oriented its body in one of 21 characteristic postures (below) toward the other at a distance of less than 20 cm. If neither (1) or (2) occurred within 2 min after the partition was raised, the test was stopped (this happened in 2.8% of the 5. parryii trials, and in 4.0% of the S. beldingi trials, distributed about equally across groups). During a 5-min test, interactions were described into a tape recorder; the grid location of each animal was also recorded every 15 sec. When a test

6 496 W. G. HOLMES AND P. W. SHERMAN was concluded, the arena was vacuumed to remove feces and urine, and wiped thoroughly with a vinegar-dampened cloth. Audio tapes of arena interactions were analyzed after all pairs had been tested each year. Prior to the first arena test, we categorized each of the 21 possible types of encounters as neutral, exploratory, or agonistic. We recognized six neutral behaviors: extended (^3 sec) nose-body contact, lean against, crawl over, fur chew, "play," and mount (termed "cohesive" behaviors by Sheppard and Yoshida, 1971); and four exploratory behaviors: brief (^3 sec) nosenose, nose-head, nose-body, or nose-anus contact (termed "recognitive" behaviors by Sheppard and Yoshida, 1971). The reliability of Holmes's behavioral categorizations was established by practicing with videotapes of arena interactions of 10 pairs of S. parryii and 11 pairs of S. beldingi, which were made before data collection began. These tapes are now on file with the Department of Psychology, University of Michigan, Ann Arbor. Here, we analyze only the 11 behaviors categorized as agonistic (Appendix) for three reasons. First, all 11 have been observed in wild populations of S. beldingi and S. parryii, usually preceding or accompanying male-male conflicts over mates, or female-female conflicts over nest sites and territories. The form of the various agonistic behaviors in the arena was similar to that seen in the field, and to ethograms for Spermophilus species (e.g., Steiner, 1970; Sheppard and Yoshida, 1971; Watton and Keenleyside, 1973; Michener, 1974; Dunford, 1977). Second, whereas "neutral" and "exploratory" interactions could not always be separated, agonistic encounters obviously involved conflict. Finally, agonistic behaviors were consistently identified by a non-trained individual, who viewed videotapes of 10 arena tests; neutral and exploratory behaviors were not as consistently identifiable by this individual. An agonistic encounter was recorded whenever one ground squirrel directed any of the 11 agonistic behaviors (Appendix) at the other. If one animal did this and its partner responded in 2 sec or less, only the initiator's agonism was recorded. If, on the other hand, the recipient turned away from (>90 ) or moved away from (>10 cm) its opponent, and then turned back and behaved agonistically, a second agonistic encounter was recorded. If a series of interactions occurred in a short interval (3-5 sec), a single agonistic encounter of the most intense type observed in that bout was recorded. The 5-min test period was chosen after experimentation with longer times. In 1979, 12 pairs of weaned juvenile S. parryii, three from each of the four groups, were observed in the arena for 15 consecutive min. While encounter rates decreased as time passed, the percent that were agonistic, exploratory, and neutral did not change across the three consecutive 5-min time blocks (P > 0.1 for each category of behavior; one-way analysis of variance ANOVA). Also in 1979, 10 other pairs of S. parryii from various groups were observed on three different days, with a 5-day interval between each test. There were no consistent patterns of increase or decrease in total frequency of the three encounter types over the three tests. Most important, however, the percent of agonistic, exploratory, and neutral encounters did not change across the tests (P > 0.1, AN- OV A, for each general category of behavior). Thus, we decided that a single 5-min test was sufficient to assess a pair's behavior relative to that of other pairs. This paper deals with the frequency rather than the intensity of agonistic encounters during arena tests, because it was not possible to quantify the intensity of each of the 11 agonistic behaviors. Thus we report the mean numbers of agonistic encounters (±SE) per test group. To obtain these statistics, as many pairs as possible within each of the four groups were tested, with one constraint: we minimized the number of times a particular animal was tested as a member of a pair within the same group. In most cases, we obtained reasonable sample sizes without testing any individual more than once in the same group. However, in the S.RA. group (Fig. 1) for S. beldingi, 3 of 21 pairs (14%) contained the same individual, which represents the maximum number of times one

7 animal was tested in the same group for both species. On the other hand, an individual was frequently tested as a member of a pair in two different groups: thus, 76% of our experimental S. parryii and 82% of the S. beldingi were tested in two groups (e.g., a 3 and b, in Fig. 1). Juvenile S. parryii were 51 ± 1.2 days old at testing (mean ± SE). In the field, juveniles interact with both nestmates and nonnestmates at about this age. Pairs were tested during a 3-wk period beginning in late July in both years, and were housed with their rearing dam and nestmates before and after testing. In contrast, S. beldingi were not tested until they were about eight months old. Twelve pairs were observed in the laboratory arena as juveniles, but, like free-living juveniles at Tioga Pass, rarely behaved agonistically. Thus, born animals were housed with their dam and their nestmates until September Then each animal was housed individually in a small (25.4 x 17.8 X 16.5 cm) hibernation cage, given burlap for nesting material (ca. 1.5 m 2 /animal), and placed in a cold room (ca. 5 C). In March 1980, animals were taken from the cold room, housed in individual cages, and given food and water. Testing began 10 days later, and testing lasted 15 days. Yearling 5. beldingi thus averaged 257 ±1.8 days old when they were tested; at testing, males had slightly pigmented scrota and females had slightly swollen vulva. Field study animals KIN RECOGNITION IN GROUND SQUIRRELS 497 The Belding's ground squirrels living on Tioga Pass Meadow have been studied since During these years, 3,051 animals, including all 1,154 young from 237 litters, have been individually marked with eartags, or by clipping toes. Females nest alone and because juveniles were captured before litters mixed, assignment of young to sibling groups was unambiguous. Ground squirrels were live-trapped using peanut butter as bait, and handled with gloves; they were not anesthetized. All study animals were marked individually with human hair dye (black) and were observed from trees or 2-3 m tall tripods, usually with binoculars. Data were recorded in notebooks, on prepared checksheets, or on tape. Kinship assessment in S. beldingi Littermates emerging from the same natal burrow were captured and marked before litters mixed up. Thus matrilineal relationships were determined directly. However, patrilineal relatedness among descendant and collateral kin was less certain, because female S. beldingi typically mate repeatedly with different males (x = 3.3 mates/female, range = 1 8). Recently completed paternity exclusion studies, using electrophoretically detectable allozymes from six blood protein loci, revealed that most litters (78%) were sired by more than one male (Hanken and Sherman, 1981). These same studies allowed us to positively identify some littermates as full-siblings and others as maternal halfsiblings. In this paper, "littermate siblings" means that young shared the same natal burrow and may have been full- or halfsiblings; "littermate full-siblings" means that littermates were known to have a common dam and sire; "littermate half-siblings" means that they had the same dam, but not the same sire; "nonkin" means that two animals had no known common maternal kin. Behavioral observations in the field were performed "blind" with regard to genetic relatedness among interactants. In no case did any observer, including Sherman, know the exact relationship (based on the electrophoretic analyses) of animals they were watching. Having watched animals during the 1979 breeding season, observers knew that multiple mating occurred. However, because paternity exclusion analyses on 1978 blood samples were tabulated after behavioral data were collected in 1979, observers did not know if multiple mating resulted in multiple paternity. In 1980, following completion of the first paternity exclusion analyses, observers knew that multiple paternity could occur, but they did not know if particular litters under observation were multiply sired. Behavioral observations and information derived from the paternity exclusion analyses were fi-

8 498 W. G. HOLMES AND P. W. SHERMAN nally combined in October 1980, after all the data had been gathered and tabulated. Field cross-fostering procedures for S. beldingi To investigate the ontogeny of kin recognition in free-living 5. beldingi, young were experimentally cross-fostered in 1979 and Pregnant females that provided pups for cross-fostering were live-trapped in subalpine meadows (elev. ca. 3,000 m) near Tioga Pass. They were housed at Sherman's base camp in individual stainless steel cages, and provided with a nest box, ad lib. water, mouse breeder chow, sunflower seeds, and fresh vegetables. Soon after pups were born, they were toe-clipped for permanent identification. Then, at various ages (1-50 days), these young were cross-fostered into the nest burrows of freeliving, lactating females at Tioga Pass. We attempted to match the ages of crossfostered young with those of their prospective nestmates. Although ages of field-born litters could not be determined exactly, they could be estimated using the date on which a pregnant female's body weight dropped precipitously as the day of parturition. Below, we adopt the following terminology: A "foster infant" is a pup we attempted to cross-foster into a (field) "foster burrow"; the "target dam" is the prospective dam of the foster infant; finally, "target litters" are biological offspring of target dams. Infants were cross-fostered by placing them in a grass lined nest that was constructed near the mouth of the target female's burrow. Infants were placed there as soon as possible after she emerged to feed. When she returned, the target female usually sniffed and licked the foster infant, then took it into her burrow (Michener, 1971, reported similar retrieval of pups by captive, lactating Richardson's ground squirrels). If the target dam did not return within an hour of departure, or if she returned and ignored the infant, the foster pup was returned to its biological dam; this occurred in 8% of cross-fostering attempts. When infants became ambulatory and their eyes opened {ca. 23 days of age), they often refused to stay in the grass cradle. Such infants were placed directly into the mouth of the target burrow soon after the target dam had exited. These latter cross-fosterings mimic natural mixups of young that sometimes occur when newly emerged juveniles enter neighboring natal burrows (Sherman, 1980a). An infant was scored as "accepted" if it remained with its nestmates at least 1 wk after the target litter first emerged. If no young ever emerged from a target burrow (suggesting disease or predation), the transferred infant was omitted from the analysis. Young introduced after a target litter had emerged were considered accepted if they continued to use the target burrow for 1 wk. Sibling recognition was investigated only between yearling females, for two reasons. First, although juveniles interact extensively after emergence, it is not possible to clearly separate their play-like behavior into acts of aggression or amicability. Second, because juvenile males disperse a few weeks after emergence, only sister-sister recognition could be studied. Sibling recognition data were therefore collected in 1980 by observing females that had been crossfostered in Thus, we observed the behavior of female yearlings that were Nonsiblings-Reared Together and Siblings-Reared Together. Field observation of S. beldingi behavior Subsequent to parturition, maternal females protect their young from infanticide, a major source of juvenile mortality (Sherman, 1981a), by defending the area surrounding their nest burrow. They attack and vigorously chase all conspecifics except their closest female kin from this territory. To investigate sibling recognition, we recorded five types of social interactions associated with territorial defense by reproductive (pregnant or lactating) yearling females: (1) Chases one female pursues another for at least 1 m; chases interrupted by brief pauses (= 5 sec) were recorded as one; (2) Trespasses one female intrudes into the territory of another when the owning female is on the territory and aboveground; an "encounter" occurred between them if they came within 0.5 m of each other; (3) Fights aggressive interactions involving violent physical con-

9 tact (Appendix); fights interrupted by brief breaks in contact (= 5 sec) were counted as one; (4) Cooperative Chases a female joins an ongoing chase, which is not occurring on or headed into her territory, on the side of the chaser; this usually results in the rapid expulsion of the intruder; (5) Assistance while being chased a female joins an ongoing chase, which is not occurring on or headed into her territory, on the side of the chasee; this intervention usually results either in the termination of the chase or a reversal of the original chaser-chasee roles. For each interaction between two individuals, only one type of social encounter (the first occurring) was analyzed. Statistical analyses Laboratory data met the requirements of parametric statistical procedures and were analyzed by means of ANOVAs, Scheffe's tests, or <-tests (Sokal and Rohlf, 1981). S. parryii data from 1978 and 1979 were pooled because no significant between-year differences were found in agonistic encounters (P>0.1, -tests between years for each of the four groups). Field data on S. beldingi were analyzed with nonparametric tests because sample sizes were sometimes small and parametric assumptions violated (Siegel, 1956; Hollander and Wolfe, 1973). Two-sample comparisons were made with Mann-Whitney U tests. In all cases, differences between groups were considered significant if P = 0.05; P values are reported in the text and figures. RESULTS Sibling recognition in S. parryii: Laboratory tests Five-minute arena tests of Arctic ground squirrels revealed that neither (1) the time between raising the partition and the first movement by either animal, (2) the time until the first social encounter, nor (3) the mean distance between animals during the test varied among groups (P >0.1, AN- OVA in all cases). However, there were significant between-group differences in the total number of agonistic encounters (P < 0.001, ANOVA, Fig. 2). There was also significant between-group heteroge- KIN RECOGNITION IN GROUND SQUIRRELS 499 c 'E m u c UJ o Vi 0).a o a> I I S. parryii F = 25.6 P<.000l Scheffe's Contrasts S.RA. NS.RT NS.RA. S.RT. T S.RA. NS.RT ' S.RT S.RA. NS.RT. NS.RA. Pairs FIG. 2. Mean number (±SE) of agonistic encounters observed during arena tests of pairs of juvenile Arctic ground squirrels. Numbers of pairs tested are shown inside bars. The F value is based on a one-way AN- OVA. Scheffe's contrasts provide significance levels (P<) for each of the six unique comparisons between any two groups' means. For example, Siblings-Reared Apart (S.RA.) were significantly less agonistic than Nonsiblings-Reared Apart (NS.RA.) at the P < 0.02 level. Pairs are identified in Figure 1. neity in the percent of all encounters that were agonistic (P < 0.001, ANOVA), the between-group pattern being the same as in Figure 2. Thus the asymmetries in the frequency of agonistic encounters were not due simply to between-group differences in the total number of all encounters observed (agonistic + neutral + exploratory). Therefore, we have chosen to present our laboratory data as the number of agonistic encounters rather than the percent of such encounters (regardless of which measure we chose, results of statistical tests were similar). We examined the S. parryii data further to see which pairs of groups differed. Scheffe's tests revealed that juveniles reared together, both siblings and nonsiblings,

10 500 W. G. HOLMES AND P. W. SHERMAN in II (/) Q 8 t 5 o a> E a P<.5 S.RA. NS.RA. I?<.O8 m-m f-f m-f Sex of Pair FIG. 3. Mean number (±SE) of agonistic encounters during arena tests of Arctic ground squirrels that were reared apart. Means are presented for pairs of Siblings-Reared Apart (S.RA.) and Nonsiblings-Reared Apart (NS.RA.). Significance levels come from Scheffe's contrasts that were performed after three separate ANOVAs, one each on male-male (m-m), female-female (f-f). ar d male-female (m-f) pairs, revealed significant differences across the four groups (P < for all three ANOVAs). were significantly less agonistic than pairs reared apart (Fig. 2). Furthermore, sibs and nonsibs reared together did not differ in agonism. Interestingly, however, siblings reared apart were significantly less agonistic than nonsiblings reared apart (P < 0.02). While ground squirrels tested in the S.RA. group did not associate directly with each other after parturition, most of them were reared in a nest box with at least one of their other siblings; the possible effects of this are discussed below. In summary, regardless of relatedness, animals reared together rarely fought; among juveniles reared apart, genetic siblings were less agonistic in arena tests than nonsiblings. We analyzed the data further by partitioning the S.RA. and NS.RA. groups into like and mixed sex pairs (Fig. 3). We found that only for female-female pairs was there an effect of relatedness. That is, brothers reared apart and brother-sister pairs reared apart were as agonistic as nonsibling male pairs and unrelated male-female pairs, respectively. Only sisters reared apart were significantly less agonistic than unrelated females reared apart (P < 0.01). Thus, sister-sister pairs were primarily responsible for the difference between siblings and nonsiblings reared apart (Fig. 2). We also analyzed data from the S.RT. group in greater detail. First, we contrasted agonism between siblings reared by their biological dam with siblings reared by a foster dam. No significant difference was apparent (P > 0.1, Mest). Second, we contrasted siblings reared only with siblings versus siblings reared with both biological and foster siblings. Again there was no significant difference in agonism between pairs from mixed sibling and pure sibling litters (P > 0.1, t-test). In these two tests, data were not partitioned by sex for analysis because resultant sample sizes were too small. Sibling recognition in S. beldingi: Laboratory tests In S. beldingi (as in S. parryii) neither (1) the time between raising the partition and the first movement by either animal, (2) the time until the first social encounter, nor (3) the mean distance between animals during the 5-min test varied among groups (P>0.1, ANOVA, in all cases). Again, there was significant between-group heterogeneity in the total number of agonistic encounters (P < 0.001, ANOVA, Fig. 4). The same heterogeneity was evident when the percent of agonistic encounters was analyzed (P < 0.001, ANOVA). Therefore, we also present for S. beldingi the total number of agonistic encounters rather than the percent of all encounters that were agonistic. Scheffe's test for between-group differences revealed that pairs which had been reared together, whether siblings or nonsibs, were significantly less agonistic than pairs reared apart (Fig. 4). However, siblings and nonsibs reared together did not differ in agonism. Among animals reared

11 KIN RECOGNITION IN GROUND SQUIRRELS 501 S. beldingi in in h. a> o LJ o "to I l F = 36.8 P<.000l Scheffe's Contrasts &RA. NS.RT. NS.RA. S.RT S.RA NS.RT..00 II i m (O c I LLJ o I I T - P<.2 I?<.O5 S.RA. NS.RA. I o! c o a> 1 S.RT. S.RA. NS.RT. NS.RA. Pairs FIG. 4. Mean number (±SE) of agonistic encounters between pairs of yearling Belding's ground squirrels during arena tests. Details in Figure 2. C O ilii ^ m-f m-m f-f Sex of Pair FIG. 5. Mean number (±SE) of agonistic encounters during arena tests of yearling Belding's ground squirrels that were reared apart. Details in Figure 3. apart, siblings were less agonistic than nonsiblings, but this difference was not quite significant (P < 0.06, Fig. 4). We subdivided the animals that were reared apart into like and mixed sex pairs (Fig. 5). This revealed that sisters reared apart were significantly less agonistic than unrelated females reared apart (P < 0.05), whereas relatedness did not seem to affect agonism between male-male or male-female pairs (P>0.1). We also examined differences in agonism between (1) siblings reared together by their own dam versus siblings reared together by a foster dam, and (2) siblings reared in pure sibling litters versus siblings reared in mixed sibling litters. Analyses of like and mixed sex pairs combined revealed no significant differences for either (1) or (2) (P > 0.1, both tests). Thus, yearling Belding's ground squirrels behaved like juvenile Arctic ground squirrels in our laboratory tests. Recognition in S. beldingi: Field tests Dam-offspring recognition. The proportion of field cross-fostered infants that were "accepted" varied with their age at transfer and thus with the age of the target litter (Fig. 6). The majority (88% to 66%) of young cross-fostered before they were 23 days old were still using their foster burrow a week after the first emergence of the target litter. There was a sharp drop (to between 33% and 0%) in the frequency of acceptance when juveniles reached about 25 days of age; this drop roughly coincides with the emergence of the target litter. Thus, prior to the target litter's emergence, 75 ± 9% of cross-fostered infants were accepted, but only 21 ± 12% of them were accepted thereafter (P < 0.01). This suggests that the onset of dam-offspring recognition may coincide with the emergence of each dam's litter. Indeed, when their own young emerged, dams began

12 502 W. G. HOLMES AND P. W. SHERMAN T Total N = 86 < o» >- in a Birth Eyes Emergence Open (Weaning) Age at Transfer (Days ) FIG. 6. Proportion of S. beldingi young at Tioga Pass that were cross-fostered at various ages and accepted into field foster burrows. Age at transfer (e.g., 0, 5, 10 days, etc.) refers to the age of fostered young, which matched the age of the target litter. Numbers above bars refer to the number of attempted cross-fosterings. "Accepted" defined in text. attacking newly cross-fostered pups; additionally, weaned pups often attempted to flee from foster burrows. Sibling-sibling recognition. To investigate the ontogeny of sibling recognition, crossfostered females that were "accepted" as juveniles (Fig. 6) were observed as yearlings. Accepted foster nestmates and littermate sisters fought (Fig. 7a) and chased (Fig. 7b) each other equally infrequently and cooperated to chase potential trespassers (Fig. 8a) and assisted each other during chases equally often (Fig. 8b). Although sample sizes are small, young transferred after the target litter's emergence fought and chased each other significantly more often than littermates or early transferred young, and cooperated in chases and assisted each other during chases significantly less often. Thus, interactions between young transferred prior to weaning and foster sisters were indistinguishable from those between littermates, whereas the behavior of young transferred after weaning and foster sisters was indistinguishable from that of nonkin. Full-sibling vs. half-sibling recognition. The high frequency of multiple paternity in S. beldingi litters (Hanken and Sherman, 1981) provided us with an unexpected opportunity to observe yearling females that shared a natal burrow, but that were not equally related. Electrophoretically identified pairs of reproductive full-sisters (n = 13 pairs) and half-sisters (n = 12) were watched as they established nest burrows and defended territories in 1979 and These "blind" observations suggested, to our surprise, that differently related littermates may be distinguished. In our behavioral sample, full-sisters fought significantly less often when they encountered each other than did half-sisters (Fig. 9a) and chased each other from their territories significantly less often than they chased half-sisters (Fig. 9b). Full-sisters also came to each other's assistance while being chased slightly more often than did half-sisters (Fig. 10b). Finally, full- and half-sisters cooperated to chase intruders about equally frequently (Fig. 10a). Thus according to our behavioral measures, free-living yearling females favored their littermate fullsisters over half-sisters slightly (Fig. 10a, b) or significantly (Fig. 9a, b). The implication of these preliminary data is that fe-

13 KIN RECOGNITION IN GROUND SQUIRRELS o.i5-i (a) * 0.15 G o.io o oi H m OS Litt.rmate " »Nonkin- Sisters (20) (81 (9) (6) (4) (g9, (52) Age at Transfer (Days ) the Previous Year FIG. 7. Aggression among yearling female Belding's ground squirrels at Tioga Pass, depending on their age at transfer into foster burrows the previous year {e.g., 0-7 days old, 8-15 days old, etc.). Numbers of pairs in parentheses. Each animal was observed as a member of no more than two pairs within one age group. Sample sizes for Days and are small because young transferred the previous year at these ages were rarely accepted (Fig. 6). Significance levels indicate adjacent groups that differed significantly (e.g., day old transfers versus day old transfers differed significantly in their frequency of fights/encounters at P < 0.01). (a) Mean proportion (±SE) of fights per encounter on a female's territory between pairs of littermate sisters, cross-fostered nestmates, and nonkin (see text). (b) Mean proportion (±SE) of chases of trespassing littermate sisters, cross-fostered nestmates, and nonkin by territory-holding females (see text). male 5. beldingi may discriminate among nestmates, and that relatedness may affect the process. DISCUSSION Laboratory and field data Our laboratory and field data (Figs. 2-10) suggest four hypotheses about the ontog- 'S 0.00 Littermate Sisters [52] "Nonkin" (20) (8) (9) (6) U) e9) Age at Transfer (Days) the Previous Year FIG. 8. Cooperation among yearling female Belding's ground squirrels at Tioga Pass, depending on their age at transfer into foster burrows. Number of pairs in parentheses, with additional details in Figure 7. (a) Mean proportion (±SE) of cooperative chases in which residents were joined by their littermate sisters, cross-fostered nestmates, and nonkin to evict intruders (see text). (b) Mean proportion (±SE) of chases in which females being chased were assisted by their littermate sisters, cross-fostered nestmates, and nonkin. eny and specificity of kin recognition in our ground squirrels: /. The ontogeny of sibling recognition depends on association in the natal nest. In the laboratory tests with both S. beldingi and S. parryii, siblings and nonsiblings that were reared together, whether in "pure" sibling or mixed, cross-fostered litters, were less agonistic than siblings or nonsiblings reared apart (Figs. 2 and 4). Whether or not a pair was related did not seem to affect their arena behavior if they had shared a common nestbox. In thefield, juvenile female S. beldingi that were transferred into nest burrows before their foster-nestmates

14 504 W. G. HOLMES AND P. W. SHERMAN c o o c LLJ Ol O-15-i (a) \ I ( b ) o> in o I P<.05 I P<.05 X S i 1 Littermate Littermate Sisters Full- Half- (52) Sisters Sisters (13 prs., from (12 prs., from 11 litters) 8 litters ) FIG. 9. Aggression among yearling female S. beldingi that were reared with both full- and maternal halfsiblings at Tioga Pass. Genetic relatedness was determined by electrophoretic analyses of blood proteins; observations were performed "blind" (see text). (a) Mean proportion (±SE) of fights per encounter on females' territory between pairs of littermate sisters (full- and half-sisters combined), full-sisters, and maternal half-sisters. Of the 134 fights between littermate sisters, the range contributed by any two pairs was 2 14 fights. The range was1 6 of the 31 total fights between full sisters. For half-sisters, the range was 2-7 of the 40 total fights. (b) Mean proportion (±SE) of chases per trespass on females' territory between littermate sisters, fullsisters, and maternal half-sisters. Of all 173 chases between littermate sisters, the range contributed by any two pairs was 4-17 chases. The range was 2 7 of the 39 total chases/trespasses between full-sisters. For half-sisters, the range was 1-7 of the 49 total chases/ trespasses. For both (a) and (b), full- and half-sisters came from a different sample of litters than littermate sisters. Numbers in parentheses give the number of dyads in each category. Eight pairs of full-sisters and 6 pairs of half-sisters were unique, i.e., both females were observed as members of one and only one pair within a category of relatedness. emerged aboveground (i.e., before they were 3 wk old) were treated like littermate sisters as yearlings, whereas juveniles transferred during their 4th to 7th week U) o c o O O O a, s , (a)i (b) i \P=.090 P=.O52 \ I 0.00 Littermate Littermate Sisters Full- Half- (52) Sisters Sisters (13) (12) FIG. 10. Cooperation among yearling female Belding's ground squirrels that were reared with both full- and maternal half-siblings at Tioga Pass. (a) Mean proportion (±SE) of cooperative chases in which residents were assisted by their littermate sisters, full-sisters, and maternal half-sisters to evict intruders. Of all 150 cooperative chases involving littermate sisters, the range contributed by any two pairs was 0 12 chases. The range was1 5 of the 32 total cooperative chases involving full-sisters. For half-sisters, the range was 0-6 of the 41 total chases. (b) Mean proportion (±SE) of chases in which females being chased were assisted by their littermate sisters, full-sisters, and maternal half-sisters. Of all 110 such cases involving littermate sisters, the range contributed by any two pairs was 0-9 chases. The range was 0 5 of the 27 total chases involving fullsisters. For half-sisters, the range was 0 3 of the 23 total chases. See Figure 9 for details. were treated more like nonkin as yearlings (Figs. 7 and 8). In free-living 5. parryii and S. beldingi, recognition of siblings based on their association in the natal nest would seldom lead to mistaken identification. This is because unrelated ground squirrel pups rarely, if ever, share a natal burrow prior to weaning. For example, in four field sea- i

15 sons at Tioga Pass, Sherman (1980a) witnessed only six instances of natural mixing-up in about 100 hr of close observation on 173 juvenile Belding's ground squirrels. In these cases, a newly emerged pup entered a natal burrow other than its own and remained there until its younger foster littermates emerged. The following year, foster sisters treated the foreign females (n = 3) like littermates, and vice versa. In contrast to female S. beldingi, which nurse their young in separate burrows, about half of Arctic ground squirrel dams carry their young to a common burrow just prior to weaning (McLean, 1981). Females who share burrows in this way are typically dam-daughter or sister pairs. The result of such aggregation is that 5. parryii pups contact conspecific juveniles other than littermates at an earlier age than do S. beldingi pups. We predict that due to this early mixing-up, the onset of sibling recognition should occur earlier in the development of juvenile S. parryii than S. beldingi. II. Discrimination of siblings is not always contingent on their being reared together. In both S. parryii and S. beldingi, sisters reared apart were less agonistic in laboratory tests than unrelated females reared apart (Figs. 3 and 5), whether the unrelated females were reared with siblings alone or with both siblings and nonsiblings. Relatedness did not significantly affect the arena behavior of brother-brother or brother-sister pairs reared apart. Either these pairs do not recognize each other, or they lack the motivation (Myrberg, 1966) of sister-sister pairs to make the discrimination. Regardless, the sister-sister data are intriguing because they suggest that (1) sisters who have not had extensive postnatal contact can nonetheless recognize each other, and (2) this recognition ability is asymmetrically expressed in females, the more nepotistic sex in the field. Regarding (1), "postnatal contact" must be emphasized given the known effects of prenatal experience on postnatal social behavior (Clemens, 1974) and social preferences (vom Saal and Bronson, 1978). Perhaps of greater importance than possible in utero effects were the nestmates with whom sisters reared apart did associate. For KIN RECOGNITION IN GROUND SQUIRRELS 505 example, it seems possible that females learned something about the phenotypes of their sibling or nonsibling nestmates during rearing (e.g., odors; see Halpin, 1980), and then used this information to identify sisters with whom they were not reared (e.g., Buckle and Greenberg, 1981). Although animals in the S.RA. group did not associate during rearing, each subject may have been raised with other siblings. For example, (Fig. 1) bj and b 4 were reared apart and then tested in the S.RA. group; note that b, had shared a nestbox with its sibling b 3, while b 4 was reared with its sibling b 2. It seems possible that females b, and b 4 learned something from associating with b 3 and b 2, respectively, and used this to identify each other. We examined this possibility for 5. parryii only, sample sizes for S. beldingi being too small to permit a similar test. Ten of the S.RA. pairs were identified in which each subject had been reared with the same number of sibs (none to three). Using our arena test data, we contrasted the number of agonistic encounters observed between sisters reared apart and the number of siblings with whom each female was reared. We discovered that the more siblings each sister was reared with, the less agonistic were these S.R.A. pairs in arena tests (r = -0.72, P < 0.05). This significant negative correlation is consistent with a kin recognition mechanism which involves learning nestmates' phenotypes. However, our sample size is currently too small to permit a more detailed examination of the mechanism. Furthermore, although each female in our sample was reared with an equal number of biological siblings, their sex ratio was not always the same, and the number of nonsiblings with which each female was reared was not always equal. Thus, whether female ground squirrels identify unfamiliar sisters based on their similarity to nestmates (e.g., Buckle and Greenberg, 1981) or similarity to their own phenotypes is currently unknown. ///. The onset of dam-offspring and siblingsibling recognition in S. beldingi occurs coincident with aboveground emergence. There is a temporal component to dam-offspring and sibling-sibling recognition in Belding's

16 506 W. G. HOLMES AND P. W. SHERMAN ground squirrels. In the field, the likelihood that dams would accept foreign young changed dramatically at about the time their own pups were weaned and began to emerge aboveground (Fig. 6). Thus, as in other group-living species (e.g., crested terns, Sterna bergii, Davies and Carrick, 1962; ring-billed gulls, Larus delawarensis, Miller and Emlen, 1975; various swallows, Hoogland and Sherman, 1976; Burtt, 1977; Beecher et al, 19816) the onset of parent-offspring recognition coincides with the time when distantly related or unrelated juveniles first mix. The onset of sibling recognition also seems to occur coincident with emergence above ground and weaning, when the juveniles are about 3 wk old (see above and Figs. 7 and 8). TV. Female Belding's ground squirrels may discriminate between littermate full-sisters and maternal half-sisters. In the field, electrophoretically identified full-sisters and maternal half-sisters seem to treat each other differently as yearlings: in our sample the former were less agonistic and more cooperative (Figs. 9 and 10). These behavioral observations are especially intriguing because full- and half-sisters shared not only a common nest burrow, but also a common uterus. (However, we have no information about in utero positions of fullversus half-sisters.) Although we regard our data as preliminary, they imply that sibling recognition in S. beldingi is augmented by some mechanism in addition to association in the natal burrow. Research techniques and "paradoxical" results Four comments may help the reader to identify weaknesses and strengths in our data, and thus assist in interpreting our results. First, our laboratory and field observations were not truly "blind," because individuals gathering the data were usually aware of the hypotheses being tested. However, in laboratory tests a technician brought subjects into the observation room in a randomized order unknown to the observer (Holmes). In the field, Sherman and his assistants did not consult the electrophoretic results until after the behavioral data had been compiled. Second, in this paper we have investigated the effects of rearing environment and relatedness on recognition of kin classes; we do not know if individual recognition of kin (e.g., Halpin, 1980) occurs in either ground squirrel species. Unlike several other studies of recognition (e.g., DeCasper and Fifer, 1980; Wu etal, 1980; Blaustein and O'Hara, 1981), we used dyadic encounters in our study rather than tests of a single individual's discriminatory abilities. Accordingly, we could not determine if, for example, a sister reared apart from her brother could recognize him even if he could not identify her. Neither could we simultaneously present a test subject with a choice between a familiar and an unfamiliar sibling. One possible justification of our dyadic encounter method is that in the field female S. beldingi often encounter conspecifics sequentially rather than simultaneously. That is, opportunities for them to choose between simultaneously appearing conspecifics happen relatively rarely. The paired-encounter protocol for our laboratory tests paralleled this field situation. Third, our laboratory measure of sibling recognition, total number of agonistic encounters, was an unweighted combination of all 11 agonistic behaviors (Appendix). We did not address the question of whether specific behaviors characterized certain relatedness X rearing groups. However for both species, frequencies of the most commonly observed agonistic behaviors closely match the combined total amount of agonism: S.RT. < NS.RT. < S.RA. < NS.RA. (Table 1). Finally, discrimination by free-living female S. beldingi between full- versus maternal half-sisters (Figs. 9 and 10) seems, at first, to contrast with the absence of differential agonism between (1) S.RT. versus NS.RT. in the laboratory (Fig. 4) and (2) cross-fostered nestmates (less than 25 days of age) versus biological littermates in the field (Fig. 6). (In regard to (1), Fig. 4 shows laboratory results without regard to the test pairs' sexes, whereas Figs. 9 and 10 present data for females only. If only data for female-female pairs were graphed in Fig. 4, S.RT. and NS.RT. would be similar and thus contrast paradoxically with Figs. 9 and 10.) We believe that "laboratory paradox

17 KIN RECOGNITION IN GROUND SQUIRRELS 507 TABLE 1. Frequency (and per cent) of most common types of agonistic encounters recorded during laboratory tests of S. parryii and S. beldingi. Arctic ground squirrels 0 Lateral Fight Paw swipe Chase Squeak/squeal Belding's ground squirrels 1 ' Lateral Paw swipe Withdraw "Threat" vocalization Lunge strike Fight Sibs- Reared Together 41 (14.3)" 3 (2.7) 3 (2.7) 2 (4.9) 6 (20.7) 0 (0.0) 2 (3.6) 3 (8.3) 0 (0.0) 0 (0.0) 0 (0.0) Sibs- Reared Apart 84 (29.3) 31 (27.7) 40 (36.6) 12 (29.3) (17.2) 34 (47.2) 21 (37.5) 18 (50.0) 9 (30.0) 9 (47.4) 2 (16.7) Group 0 under observation Nonsibs- Reared Together 44 (15.3) 14 (12.5) 9 (8.3) 3 (7.3) 0 (0.0) 7 (9.7) 2 (3.6) 0 (0.0) 0 (0.0) 1 (5.3) 2 (16.7) a See Figure 1 for explanation. " Percent of all lateral behaviors attributable to the S.RT. group. c These five types of encounters account for 81.4% of all agonistic encounters. " These six types of encounters account for 84.5% of all agonistic encounters. Nonsibs- Reared Apart 118 (41.1) 64 (57.1) 57 (52.3) 24 (58.5) 18 (62.1) 31 (43.0) 31 (55.4) 15 (41.7) 21 (70.0) 9 (47.4) 8 (66.7) All pairs (1)" reveals the limitations of our arena test- havior of full- and half-siblings (for S. beling procedure: pups reared in the same dingi at least), possibly obscuring any difnestbox were so rarely agonistic (Figs. 2 ferences that may have existed between and 4) that differentiation between the S.RT. and NS.RT. The apparent "field S.RT. and NS.RT. groups would be ex- paradox (2)" is discussed below under tremely difficult on the basis of our sam- "Phenotype matching in ground squirrel pie, even if differences existed. Further- kin recognition?" more, in the field, yearling S. beldingi were observed over the entire summer (3 mo). Mechanisms of km recognition During this time we accumulated data that, W. D. Hamilton's (1964) inclusive fitness taken together, revealed slight differences hypothesis predicts that genetic relatedin behavior between full- and half-sisters; ness will be important in the evolution of such differences were not necessarily ap- behavioral interactions in social species parent during any brief series of field en- (particularly nepotism and inbreeding counters. In contrast, laboratory observa- avoidance). Hamilton's hypothesis thus tions were confined to a single 5-min provides an evolutionary explanation for period. Lastly, intra-litter paternity was the role of kinship in social behavior. It unknown for our laboratory test subjects, does not depend on any particular proxi- Thus, our data probably combined the be- mate mechanism of kin identification. We

18 508 W. G. HOLMES AND P. W. SHERMAN suggest, in agreement with Alexander (1979, p. 105) that there are at least four proximal mechanisms of kin recognition (also Hamilton, 1964, p. 21; Holldobler and Michener, 1980, p. 35; Sherman, 1980a, p. 524; Bekoff, 1981, p. 313): (1) spatial distribution, (2) association, (3) phenotype matching, and (4) "recognition alleles." Kin recognition mechanisms are selected in the contexts of facilitating nepotism and preventing consanguineous matings when inbreeding is deleterious. Thus, relatives may be "unrecognizable" because in the evolutionary past (1) it has not been reproductively advantageous to favor them (Hamilton, 1964), (2) consanguineous matings have not been disadvantageous, or (3) kin have not been consistently accessible or available for social interactions due to patterns of dispersal or mortality (Sherman, 1980a). To argue that nepotism is limited by cognitive abilities to identify kin is to confuse proximal and ultimate levels of analysis. Likewise, to suggest that preferential treatment of "siblings" is "only" preferential treatment of young that grew up together (e.g., Washburn et al., 1965) is to obfuscate the distinction between one possible mechanism of kin recognition (association) and the likely adaptive function of such discrimination. Here we briefly explore the four possible mechanisms of kin recognition. By separating them, we are not implying that they are mutually exclusive. More than one could operate at a given time {e.g., Barnett, 1982), and individuals might rely on different mechanisms according to age (e.g., Myrberg, 1975), sex (e.g., Labov, 1980), and sensory capabilities (e.g., mammals: Eisenberg and Kleiman, 1972; Doty, 1976). Nonetheless, we feel that it is useful to make the following distinctions: /. Recognition by spatial distribution. If kin are distributed predictably in space, nepotism might occur by favoring conspecifics encountered at particular locations relative to, for example, a home territory or nest. Likewise deleterious consanguineous matings would be reduced if members of one sex avoided potential sexual partners encountered at such locations. In both cases, the "recognition" of kin would be indirect: although conspecifics are treated differently according to their relatedness, locations where relatives are likely to be encountered, rather than kin themselves, are identified. Examples include nest recognition by parent gulls before their chicks are ambulatory (Cullen, 1957; Davies and Carrick, 1962; Miller and Emlen, 1975) and by parent swallows before nestlings fledge (Hoogland and Sherman, 1976; Burtt, 1977; Beecher et at, \9S\b), or nest site recognition in philopatric polistine wasps, leading to sibling reaggregation and cooperation (West Eberhard, 1969; Klahn, 1979; but see Noonan, 1981; Ross and Gamboa, 1981). This mechanism will obviously be disfavored in highly dispersive species and if relatives do not remain in appropriate locations or nonkin frequently infiltrate. //. Recognition by association. If relatives predictably interact in unambiguously appropriate social circumstances, recognition may be facilitated by a mechanism involving direct association (termed "social learning" by Alexander, 1979, p. 108). Unambiguous circumstances are those in which kinship is unlikely to be diluted or erased by differences in relatedness among interactants (e.g., mixing of full- and half-siblings, or by mixing of different families). Most often interactions in the natal nest provide the right opportunities for social learning of relatives. This mechanism is appropriately suspected if young can be successfully cross-fostered early in development (e.g., Klopfer and Klopfer, 1968; Noakes and Barlow, 1973; Burtt, 1977; Kukuk et al, 1977). For example, spiny mice recognize as "siblings" pups with whom they shared a nestbox (Porter et al., 1978; Porter and Wyrick, 1979), even if they are not related (Porter et al., 1981). Likewise, in Richardson's ground squirrels, nestmates (Sheppard and Yoshida, 1971) and dam-infant pairs (Michener and Sheppard, 1972; Michener, 1974) that associated during lactation were less agonistic and more cohesive in later laboratory tests than were pairs that had not previously associated. In bank swallows (Beecher et al., 1981a, b) and many gull species, parent-offspring vocal recognition is prob-

19 ably based on social learning just before chicks become ambulatory (Evans, 1970a, b; Miller and Emlen, 1975; evidence reviewed by Beer, 1970). In all of these examples, individuals being studied had associated directly with each other during juvenile development. There is also an association mechanism not involving prior direct contact that merits consideration. Relatives might conceivably recognize each other if they predictably met in the presence of a third individual who was familiar to both of them. For example, recognition between maternal half-siblings produced in different years might be facilitated by interactions in the presence of their common, familiar dam (Sherman, 1980a, p. 533; Meikle and Vessey, 1981). Paternal recognition of pups in wild-strain house mice (Mus musculus) may also involve such a mechanism (Labov, 1980). In the laboratory, males were allowed to copulate and then were separated from their mates. After various lengths of time the males were reunited with either a female they had inseminated or one inseminated by another male. Labov (1980) reported that males were less likely to kill young their partner bore the longer the pair had associated prior to parturition, regardless of whether or not the male actually sired the pups. Here paternal "recognition" of pups may have been mediated through recognition of the mate or the length of time spent with her. Perhaps, as Labov (1980) suggests, under normal circumstances the act of copulation and the length of malefemale cohabitation provide a way for males to assess paternity (see also vom Saal and Howard, 1982). ///. Recognition by phenotype matching. If phenotypic similarity is correlated with genotypic similarity, unfamiliar conspecifics might recognize each other by "comparing phenotypes" (Alexander, 1979, p. 116) with those of familiar relatives. Under this hypothesis, recognition of unfamiliar animals as relatives would occur by a process of phenotype matching: an individual learns and recalls its relatives' phenotypes or its own phenotype, and compares phenotypes of unfamiliar conspecifics to this learned "template." Any phenotypic traits might be KIN RECOGNITION IN GROUND SQUIRRELS 509 compared, depending on the sensory systems used in social encounters and on inter-individual variation in phenotypes {e.g., Barrows et al., 1975; Crozier and Dix, 1979; Beecher, 1982; Lacy and Sherman, unpublished data). Evidence suggesting a correlation between genotypic and phenotypic similarity exists for a variety of organisms (Pakistis et al., 1972; Carter-Saltzman and Scarr-Salapatek, 1975; Kukuk et al., 1977; DeFries, 1980; reviewed by DeFries and Plomin, 1978), and recently gathered data imply the existence of phenotype matching as a mechanism of kin recognition. Greenberg (1979) and Buckle and Greenberg (1981) have reported sibling recognition in sweat bees which seems to occur by a phenotype matching process. Among free-living L. zephyrum, females guard the entrance holes of group nests, allowing nestmates (usually sisters) to enter and rejecting non-nestmates. There appears to be a correlation between relatedness and phenotypic similarity (in odor: Kukuk et al., 1977) among these bees. When Greenberg (1979) presented unfamiliar kin to guards in the lab, he found that acceptance rate increased as relatedness increased. Buckle and Greenberg (1981) then reared guards under one of three conditions: solely with their sisters, solely with nonsisters, or with both sisters and nonsisters. When tested, guards admitted or rejected unfamiliar bees depending on intruders' relatedness to the guards' nestmates (and presumably their phenotypic similarity) rather than to guards themselves. L. zephyrum guards thus behaved as if they compared the phenotypes of unfamiliar intruders against a template learned from nestmates during rearing {i.e., phenotype matching using nestmates' phenotypes as the template). A second case of phenotype matching may occur among tadpoles of American toads (Waldman and Adler, 1979; Waldman, 1981, 1982) and Cascade frogs (Blaustein and O'Hara, 1981, 1982; O'Hara and Blaustein, 1981). In both species, when eggs were separated before hatching and tadpoles reared in social isolation, the tadpoles preferentially associated with (unfa-

20 510 W. G. HOLMES AND P. W. SHERMAN miliar) siblings rather than (unfamiliar) nonsiblings when given a choice. These intriguing results suggest that during development tadpoles might learn cues from their own phenotypes or the jelly that envelops eggs, and later recognize unfamiliar individuals as being either similar or not similar to this template. Waldman (1981) pursued this logic experimentally by inducing laboratory matings between adult B. americanus, rearing the resulting tadpoles in isolation, and then testing for discrimination between full-siblings and maternal half-sibs and between full-siblings and paternal half-sibs. He found only fullsibling versus paternal half-sibling discrimination, suggesting that some factor obtained from the mother provided the cue for recognition (e.g., a chemical in the egg or its jelly) (also see Blaustein and O'Hara, 1982). A third case of phenotype matching has been suggested to occur in domestic white leghorn chicks (Gallus gallus: Salzen and Cornell, 1968). In the laboratory, chicks were dyed various colors at hatching and reared in groups or in isolation, with or without access to drinking water in flat pans. When tested later, group-reared chicks preferentially approached conspecifics dyed the same color as cagemates. Among chicks reared alone, only those that could have seen their own reflections in their drinking water preferentially approached conspecifics dyed the same color as themselves. Based on the results of other discrimination tests, an "innate" color preference was ruled out as the main factor influencing the chicks' choices. Thus Salzen and Cornell (1968) suggested that in the absence of social experience, "selfperception" may have explained the choice behavior of the isolates. Phenotype matching may also occur in a primate. In a lab test apparatus, juvenile pigtail macaques that were reared apart from all kin looked longer at and approached unfamiliar paternal half-siblings more than unfamiliar unrelated monkeys matched for age, size, and sex (Wu et al, 1980). The only obvious kinship cue available to the young monkeys was their own phenotypes. Finally, Bateson (1980) has recently discovered that Japanese quail (Coturnix c. japonica) preferentially approach unfamiliar individuals of the opposite sex whose phenotypes are slightly different from those of conspecifics with whom subjects were reared. While these experimental results, and others summarized in this section, were based on laboratory tests and are of unknown relevance to natural situations, they nonetheless suggest that abilities to identify unfamiliar relatives exist in a variety of taxa and that phenotype matching to a learned template may be a common underlying mechanism. IV. Recognition due to "recognition alleles." Phenotype matching occurs subsequent to learning one's own phenotype or those of known kin. Phenotypes could also be used in kin recognition independent of learning through the action of hypothetical "recognition alleles" (Hamilton, 1964). If such alleles exist and could (1) express their presence phenotypically, (2) enable bearers to recognize the alleles or their effects, and (3) cause bearers to favor individuals carrying copies of them, then kin recognition via a process of direct genotypic comparison might occur. We know of no empirical evidence of this sort of recognition. However, some intriguing gene effects on recognition have been shown in congenic mice, which are laboratory animals that, through repeated inbreeding, differ from other inbred strains at one or a few loci. In mating preference tests, congenic male Mus chose females that differed genetically from them only at a point in the H-2 locus (the major histocompatibility complex) rather than genetically identical females (Yamazaki et al., 1976). These and other experiments (Yamazaki et al., 1980) suggest that, "... mating preference is governed by two linked genes in the region of H-2, one for the female signal and one for the male receptor." (Yamazaki et al., 1976, p. 1334). Although this work does not focus on kin recognition, the results suggest that small genotypic differences can affect MILS mate choice. Two theoretical arguments suggest that "recognition alleles," or the "green beard effect" (Dawkins, 1976), should be rare in nature however. First, as Hamilton (1964) pointed out, such alleles would have to be

21 KIN RECOGNITION IN GROUND SQUIRRELS 511 fairly complex to fulfill requirements (1), (2), and (3). Second, if recognition alleles caused their bearers to favor individuals of less than the mean within-brood or intrapopulation genetic relationship, they might benefit themselves and alleles closely linked to them but not the rest of the genome (Leigh, 1977; Alexander and Borgia, 1978). Thus they would be "outlaws," susceptible to being nullified by alleles at other loci which did not benefit from the recognition alleles' effects (Alexander and Borgia, 1978; but see Ridley and Grafen, 1981; Rothstein and Barash, 1982). From an empirical viewpoint, the search for hypothetical recognition alleles seems difficult at best. First, their existence could be inferred only after all other environmental and experiential cues had been eliminated (i.e., mechanisms I III); this would require prior knowledge of the cue(s) or else progressive elimination of all possible types of experience. Second, even if an individual were reared in total isolation, it is difficult to conceive of methods to deny it opportunities to gain information about its own phenotype, knowledge it might use to identify relatives. Conditions favoring phenotype matching There are at least four ecological and social circumstances when a kin recognition mechanism other than spatial distribution (I) or association (II) might be favored, if recognition occurs (Table 2). These are circumstances when associational or distributional cues are either not available or might yield inaccurate kinship estimates. In these situations, if nepotism or inbreeding avoidance occurs, discrimination based on phenotype matching (III) may be appropriately suspected. First, when females copulate with more than one male, litters may comprise full- and maternal half-siblings (refs. in Hanken and Sherman, 1981). Similarly, paternal half-sibs may result from male polygyny and these half-sibs may not be reared together. Phenotype matching seems especially likely when females are polygamous because young sharing a natal nest would have no obvious association differences on which to base full-sib versus half-sib discriminations. Sires that do not participate in rearing mates' offspring and that interact with them in their mates' absence might also rely on a matching mechanism to avoid consanguineous mating (e.g., lekking species: Wiley, 1974; ungulates: Jarman, 1974). Similarly, males that are only one of several that mate with a single female during her receptive period (e.g., Hausfater, 1975) might use phenotype matching to identify their offspring (Alexander, 1979). Second, when embryos or young are grouped, juveniles may grow up among nonkin (e.g., anuran tadpoles: Howard, 1980; O'Hara and Blaustein, 1981). Among cooperatively breeding birds (Vehrencamp, 1977; Koenig and Pitelka, 1979; Craig, 1980), nests may sometimes contain eggs of more than one pair, leading to intra-nest asymmetries in relatedness. Also, when young from different broods are reared in close proximity (e.g., cichlid fishes: McKaye and McKaye, 1977) mixing-up may occur so early in development that an individual's earliest associates are not necessarily its kindred. Third, intra-specific parasitism (e.g., many ducks: Weller, 1959), inter-specific parasitism (e.g., Payne, 1977; Rothstein, 1982), and "adoption" (McKaye and McKaye, 1977) obviously result in broods of mixed relatedness. Fourth, dispersal or large group size may favor phenotype matching as a mechanism for identifying kin. For example, individuals might leave their natal area or transfer from one social group to another before subsequent relatives are born (e.g., Packer, 1975, 1979, 1980). Or, the social group may be so large and dispersed that close kin do not meet until they are adults (e.g., social insects: Wilson, 1971). Associational and distributional cues might also be denied when embryos are deposited singly and/or there is no parental care, so that if young or parents interact they do so away from their place of birth (e.g., amphibians: Salthe and Mecham, 1974; fishes: Blumer, 1979). We re-emphasize that existence of these circumstances (Table 2) does not, by itself, favor the evolution of recognition mechanism III. However, if group-living (Alexander, 1974; Hoogland and Sherman, 1976) and nepotism (Hamilton, 1964; West Eberhard, 1975) or avoidance of consan-

22 512 W. G. HOLMES AND P. W. SHERMAN TABLE 2. Ecological and social circumstances in which phenotype matching may be favored as a mechanism of kin recognition. I. Multiple mating (A) Maternal half-siblings reared together (B) Paternal half-siblings reared apart (C) Sire-offspring recognition II. Inter-brood aggregation (A) Grouped embryos or young (B) Cooperative breeding III. Parasitism (A) Intra-specific parasitism (B) Inter-specific parasitism (C) Adoption IV. Dispersal or group size (A) Adult or juvenile relatives disperse (B) Large or widely spaced social group guineous matings (Packer, 1979; Pusey, 1980; Hoogland, 1982) is favored, under these circumstances kin recognition mechanisms not based solely on spatial proximity or direct association may be selected. Phenotype matching in ground squirrel kin recognition? Multiple paternity in S. beldingi (Hanken and Sherman, 1981) and the suggestion in our data that asymmetrical treatment of full- and half-sisters occurs (Figs. 9 and 10) raises the possibility of phenotype matching. Under this hypothesis, nestmates learn their own phenotype or those of their fullsiblings and then compare others' phenotypes with this "template." When full- and half-siblings are reared together, the second possibility requires the existence of some factor that predisposes individuals to learn differentially from them. Recall the apparent paradox (2, above) that free-living female S. beldingi discriminated between full- and maternal half-sisters, but not between cross-fostered (unrelated) nestmates and littermate sisters. Further analysis of these data revealed that cross-fostered females who were "accepted" into field nests (Fig. 6) were treated more like half-sisters than full-sisters as yearlings. That is, interactions between transferred females and their nestmates were statistically indistinguishable from interactions between littermate half-sisters (P > 0.1 for all four behaviors in Figs. 9 and 10); in contrast, the transferred females versus full-sisters comparisons mirrored the half-sister versus full-sisters comparisons shown in Figures 9 and 10. These results suggest the possibility that female 5. beldingi may make two distinctions among conspecifics, with dichotomous categories in each. First, conspecifics either shared their natal burrow, and so were classified as "littermates," or they did not (nonlittermates). Second, littermates were either relatively similar in phenotypes to them (full-siblings) or they were not (maternal half-siblings and transferred, unrelated nestmates). Although our data suggest phenotype matching with females using themselves as the referent, we cannot yet exclude the possibility that siblings' identities were learned during direct associations in utero, in the first 3 hr after birth, or sometime during development. Also, we do not yet know if ground squirrels can be reared in social isolation and can, like tadpoles of American toads and Cascade frogs, recognize siblings after experiencing only themselves during development. These questions offer intriguing possibilities for future research. CONCLUSION Interest in animals' abilities to discriminate among conspecifics has existed for many years and has been approached from several perspectives (e.g., Roy, 1980). Because of this long standing, wide ranging interest, one might have expected a spate of studies of how relatives are identified given the realization that both nepotism and avoidance of close inbreeding are widespread in nature. However, only very recently have detailed investigations of kin recognition begun to appear. Our study has revealed that both Arctic and Belding's ground squirrels are able to identify relatives. In particular, sisters reared separately behave as though they recognize each other, and free-living S. beldingi seem to differentiate between littermate full-sisters and littermate half-sisters. The ontogeny of both these abilities clearly involves learning and both relatedness and rearing environment are important to their specificity. It seems possible

23 KIN RECOGNITION IN GROUND SQUIRRELS 513 that ground squirrels identify unfamiliar conspecifics as kin or nonkin based on phenotype matching, a process which involves comparison of (genetically determined) phenotypic traits against a (learned) template. In a variety of ecological and social circumstances, direct differential association between different relatives or spatial cues about relatedness are either unavailable or inappropriate as a basis for identifying kin (Table 2). Recent investigations of kin recognition in species sharing one or more of these characteristics have nonetheless uncovered intriguing recognition abilities (e.g., Greenberg, 1979; Wu et al, 1980; Blaustein and O'Hara, 1981; Buckle and Greenberg, 1981; Waldman, 1981). These studies, coupled with the results of our investigation, suggest that abilities to compare phenotypes may be widespread and that further investigations of kin recognition by phenotype matching are warranted. ACKNOWLEDGMENTS VV. G. Holmes thanks M. Brown, J. Heerwagen, C. Rowley, and H. Wu for laboratory assistance; T. Murphy, H. Wurlitzer, and the personnel of the Institute of Arctic Biology (University of Alaska, Fairbanks) for providing equipment and assistance in the field; M. Coffey and M. Feingold of the Statistical Research Laboratory (University of Michigan) for statistical and computer advice; and G. Michener for discussions. Holmes's research was supported by a Rackham Faculty Research Grant (No ) at the University of Michigan, and by the Graduate School at the University of Washington. P. W. Sherman thanks C. Clement, L. Doyle, C. Kagarise Sherman, B. Mulder, M. Newton, S. Payne, and M. Watt for field assistance; J. Hanken, J. Sherman, K. Noack, and J. Feder for performing the electrophoretic analyses; J. Patton, F. Pitelka, and I. Zucker for providing laboratory facilities; the Clairol Company for providing hair dye; the Southern California Edison Company for housing; the California Department of Transportation for facilitating early-season travel to the study area; and F. Pitelka, S. Glickman, and R. Alexander for discussions. Sherman's research was supported by the Miller Institute (University of California, Berkeley), the Museum of Vertebrate Zoology (Berkeley), the National Geographic Society, and the National Science Foundation. For other assistance we thank R. Alexander, M. Anderson, M. Beecher, R. Caldwell, S. Glickman, W. Hamilton, K. Holekamp, M. Redfearn, C. Kagarise Sherman, R. Lacy, M. Morton, F. Pitelka, R. Smuts, and B. Waldman. The National Science Foundation and M. Beecher made possible our participation in the symposium "From Individual to Species Recognition: Theories and Mechanisms" at the December 1980 meeting of the American Society of Zoologists, where our data and ideas were first presented. REFERENCES Alcock, J Animal behavior, an evolutionary approach. 2nd Ed. Sinauer Associates, Sunderland, Mass. Alexander, R. D The evolution of social behavior. Ann. Rev. Ecol. Syst. 5: Alexander, R. D Darwinism and human affairs. Univ. of Washington Press, Seattle. Alexander, R. D. and G. Borgia Group selection, altruism, and the levels of organization of life. Ann. Rev. Ecol. Syst. 9: Barash, D. P Sociobiology and behavior. 2nd Ed. Elsevier, N.Y. Barnett, C. 1977a. Aspects of chemical communication with special reference to fish. Biosci. Commun. 3: Barnett, C Chemical recognition of the mother by the young of the cichlid fish Cichlasoma citrinellum. J. Chem. Ecol. 3: Barnett, C The development of chemosensory preferences in the cichlid fish Cichlasoma citrinellum; innate and experiential components. Behaviour. (Submitted) Barrows, E. M., W.J. Bell, and C. D. Michener Individual odor differences and their social functions in insects. Proc. Natl. Acad. Sci. U.S.A. 72: Bateson, P Optimal outbreeding and the development of sexual preferences in Japanese quail. Z. Tierpsychol. 53: Beecher, M. D Signature systems and kin recognition. Amer. Zool. 22: Beecher, M. D., I. M. Beecher, and S. Lumpkin. 1981a. Parent-offspring recognition in bank swallows (Riparia riparia): I. Natural history. Anim. Behav. 29: Beecher, M. D., I. M. Beecher, and S. H. Nichols Parent-offspring recognition in bank

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27 KIN RECOGNITION IN GROUND SQUIRRELS 517 6) Lunge strike: one animal lunges quickly toward the other, withdrawing immediately to its original position. A biting motion with incisors exposed or swipe of the paw often accompany the lunge ("Attaque frontale" Figs. 5, 7a, b in Steiner, 1970). 7) Chase: one animal briefly (ca. 2 sec) pursues the other in the arena without making contact. 8) Squeak/squeal vocalization: a single note, high-pitched call given by an animal under attack or being chased by its opponent. 9) Bite: always observed during fights (below), but recorded separately when only one animal is being bitten, usually as it tries to escape from its opponent. 10) Belly up: an animal rolls onto its back, exposing its ventral surface, opening its mouth, and everting its anal papillae (Fig. 8 in Steiner, 1970). 11) Fight: both animals are locked in a tumbling, twisting ball, accompanied by biting, scratching, and squealing or growling vocalizations (Fig. 10c in Steiner, 1970). NOTE ADDED IN PROOF A recent parallel lab cross-fostering study with Richardson's ground squirrels has revealed that siblings reared apart can identify each other as do Arctic and Belding's ground squirrels. See Davis, L. S. Sibling recognition in Richardson's ground squirrels (Spermophilus richardsonii). Behav. Ecol. Sociobiol. (In press)