Chapter 14 The Evolution of Social Behavior (1 st lecture)

Transcription

1 Chapter 14 The Evolution of Social Behavior (1 st lecture)

2 Society A group of individuals of the same species that is organized in a cooperative manner, extending beyond sexual and parental care

3 Colonial invertebrates form aggregations of individuals for mutual benefit For instance, to the right is a manof-war (phylum Coelenterata). It consists of four different types of polyps, which specialize in either flotation, feeding, defense, or reproduction

4 Sociality in Fish Form complex schools Some form colonies that actively defend nest sites Some species are territorial A school of fish changes leadership when it changes direction The leaders at the left (stippled) are shifted to the flank when the school makes at 90 degree turn, as shown in the sequence in the center and at the right

5 The colonial bluegill nests in groups Each male defends a territory bordered by the nest sites of other males. He attempts to protect his nest against bass (blue circle), bullhead catfish (green arrow), snails, and pumpkin-seed sunfish (red arrow)

6 Sociality in amphibians and reptiles Amphibians and reptiles Develop large communal sites for calling females Some exhibit parental care Some species form hibernacula (garter snakes) Some species spend considerable time and energy engaged in territorial defense

7 Males of a tropical frog (Dendrobates galindoi) wrestle for possession of a territory In most cases, spacing between frogs is maintained by repetitious calling

8 Sociality in birds The majority of bird species are monogamous territorial breeders Many aggregate in feeding, migratory and roosting flocks Well-organized breeding colonies are common The most complex avian social systems are those involving cooperative breeding, in which non-parents share in the rearing of young

9 Sociality in mammals Majority of species are solitary, where the most complex social unit is the mother with her young Some species are social during the mating season, when a male monopolizes several females (= polygynous mating system) However, complex social organizations have evolved in species within virtually all mammalian orders, especially in marsupials, carnivores, ungulates and primates that live in relatively open habitats. ==> This indicates that social behavior evolved largely as a defense against predators and protection of resources through group territory

10 Social behavior in the Hamadryas baboon A large group of baboons is departing from the communal sleeping rock (left background) on the way the the feeding and watering sites. The procession is beginning to break up into the basic social units, which consist of single males and their harems of females and offspring. Aggressive interactions are frequent and animated. The 2 males in the foreground threaten each other--the one on the right is using a hostile stare, while his opponent responds with a more intense gaping display.

11 Sociality in insects Most insects are not social. However, some species of insects (e.g., bees, ants, termites, and wasps) display a remarkable type of social organization, referred to as eusociality Eusocial insect colonies consist of: sterile workers that labor on behalf of reproductive individuals sterile worker that cooperate in the care of young at least two generations of individuals Colony members use a variety of visual and chemical signals for Alarm Simple attraction Recruitment of individuals to a new food source or nest site Grooming Greeting rituals consisting of the exchange of oral and anal liquid food Exchange of solid food particles Recognition of nestmates and members of particular castes

12 View into a termite colony Secondary queen Reproductive nymphs Primary queen Primary male Soldier

13 Haplodiploidy and the degree of motheroffspring genetic relatedness

14 Haplodiploidy and the degree of sister-sister genetic relatedness

15 The high proportion of genetic relatedness between sisters promotes the evolution of altruism among sisters, and hence the evolution of eusociality. Altruism: helpful behavior that raises the recipient s direct fitness, while lowering the donor s direct fitness Accordingly, altruistic females are presumed to be really helping their sisters (future queens) and only incidentally helping their mothers

16 Altruism in bees A female bee that has just stung a human. Notice that she deviscerates herself as she tries to leave her victim.

17 The Naked mole rat: an example of a eusocial mammal Found in Ethiopia and Kenya In the Family Bathyergidae (includes Guinea pigs, chinchillas, porcupines) Colonies: Typically rats, including workers, defenders, and a breeder (queen) Queen is very aggressive (other females reproductively suppressed until queen removed) Inbreeding high, relatedness = 0.81 (0.50 = siblings) Control over reproductive suppression: Not pheromonal, but instead due to physical contact (when queen removed, reproductivity released)

18 Genetic, ecological, and behavioral factors that appear to promote the evolution of eusociality