SOCIAL ANIMALS -Spectacular -Photographed -Studied -Appreciated The PINNACLE of evolution???
QUALITIES Social animals are aggregations of conspecifics that may have enhanced communication abilities some degree of self-sacrifice some division of labor increased genetic relatedness
Social species can range from the merely gregarious to the EUSOCIAL Gregarious tending to associate with others of one s kind. EUSOCIALITY (extreme sociality) 1) cooperation in the care of young by adults other than parents 2) overlap of generations one generation rears the next 3) CASTES that forego personal reproduction!! (1) and (2) are not surprising. (3) is radical
Locust Swarm Social Animals? no Gregarious?
Fall webworms gregarious yes. Social?
Gregarious yes Social?
SOCIAL ANIMALS
EUSOCIAL
CAUTION!! Sociality is NOT superior to solitary living why? Both are simply strategies for survival. Solitary wasp Social wasp
COST:BENEFIT ANALYSIS OF SOCIALITY Benefits: (1) protection from predators (2) Food-finding efficiency (3) Miscellaneous
(1) Protection from Predators a) The Many Eyes Hypothesis Summed sensory capacities of group members makes surprise attacks less likely.
Looking Foraging
Safety in Numbers in redshanks?
(1) Protection from Predators (continued) b) Group response causes CONFUSION http://www.youtube.com/watch?v=hibqeb6cvey
Minnow Schools: FLASH EXPANSION (advancing predator)
???
The Fountain Effect
Swirling Confusion which bird to attack?
(1) Protection from Predators (continued) c) Selfish Herd Hypothesis ( you first hypothesis) Individuals at the center of the group are safer
(1) Protection from Predators (continued) d) Numbers help defensive animals Muskoxen
(1) Protection from Predators e) the best defense is offense
Fire ant soldiers defend nests by being massively aggressive!!
Lethal temperature for invader
Bird Offense - Does Mobbing Reduce Predation? Black-headed gulls [predators are egg-eating crows] Gull colony border = gull nest Selfish Herd? outside edge center Chicken eggs placed every 10 m from outside the colony to the colony center
Effects of Mobbing by Black-headed Gulls Nest Location
(2) Food-finding Efficiency Previous examples (review): -Osprey - Honey Bees
Passive transfer of information about food location minnow school
3) Miscellaneous Benefits: Thermoregulation A small endotherm has a bad SA:VOL But, a cluster of small endotherms has a good SA:VOL High heat loss Bat cluster Low heat loss Single bat
3) Miscellaneous Benefits: Cooperation
Weaver ants cooperating to dismember a red ant
3) Miscellaneous Benefits: Cooperation Colony Heating & Cooling
3) Miscellaneous Benefits: Cooperation Weaver Ant Nest-Building
Body Bridge Group Grasping
Larva used as a weaving tool
Termite FORTRESS
Costs of Social Living: (1) Increased competition (2) Increased aggression (3) disease (4) inbreeding
Competition Example: Mexican free-tailed bat Bracken Cave (TX) 20,000,000 bats
Colony food requirement: 250,000 lbs of flying insects per night Hunting radius from cave: 100 miles!! (YCP to Philadelphia = 100 miles) BC 100 mi
Cliff Swallows Nests Swallow Bug parasites infest nests
Likelihood of Swallow Bug Infestation Infestation Level Swallow Colony Density
Effects of Swallow Bugs on Swallow Nestlings Infested nestling Insecticide-treated
Big Observation: Solitary animals are selfish e.g., bobcats don t help other bobcats rabbits don t help other rabbits Social animals are altruistic e.g., female lions will nurse some other mother s kitten soldier ants will give up their lives to protect the colony
Giant Question: Why are solitary animals selfish?? Why are social animals altruistic?? Example 1: Worker honey bee When she stings an invader, she eviscerates herself. She has committed suicide for the good of the group. WHY???
WHY?
By the time the paramedics found him near a cavern in the central Mexican highlands, the man was swollen and losing consciousness, with his pulse racing and his blood pressure plummeting. Twelve hours later, still semi-conscious and bloated and drifting into heart, kidney and liver failure, he was transferred to a Mexico City hospital. After 21 days he was released from the hospital in good health. He had been stung by Africanized honeybees more than 2000 times on the face, trunk, arms, and legs Venomous sacs were removed from all over his body, and bees were removed from his ears and nose.
Bee sting result
Honeybee Abdomen WHY??
Example 2: suicidal ant (Camponotus saundersi) Workers possess a gland that fills their abdomen. Arrival of an invader elicits massive abdominal contractio Body explodes spraying invader with sticky GOO. WHY??
WHY?.. Answer: GENETICS Social animals will make large sacrifices for genetic relatives. Class Insecta Example: Order Hymenoptera (bees, wasp, ants) Considered to be EUSOCIAL animals
Eusocial Hymenoptera have castes = group members specialized for some purpose: Queen reproduction Worker work Soldier defense CLOSE GENETIC RELATIONSHIPS
Q Order Isoptera (termites)
CONCLUSION: Sacrificing for a very close relative is no sacrifice!! If your sacrifice promotes a relative s survival, your genes are being propagated. PROFOUND CONCLUSION You don t need to reproduce to be genetically successful!!
Only 1 mammal can approach the insects in eusociality Hint: not Homo sapiens
Colony of NMRs
Zoogeography Of the NMR
NMR Observations -Not moles or rats -Underground colonies of up to 300 nmr -Poikilothermic!! Autocoprophagic!! -Castes: 1 Queen (other females don t ovulate) 2-3 mating males (other males produce sperm but don t mate) Everyone else is a worker EXTREMELY INBRED GENETIC RELATEDNESS VERY HIGH
Behavioral Castes