Sociality and Social Behaviour

Level of Sociality Mating strategy Communication System Kin Selection Altruism Predator Pressure Resource Defence Parental Care Foraging Patterns

V.C. Wynne Edwards Animal Dispersion in Relation to Social Behaviour (1962)

Reproductive restraint Function of communal displays Epidiectic display -allow animals to assess their own numbers

Reproductive restraint Epidiectic display Assessment of population size Reproductive restraint

Reproductive restraint - English Swift Commonly lays 2 eggs per clutch Can lay up to 5 eggs per clutch

Reproductive restraint - English Swift Wynne Edwards - Courtship displays allow census of local population Why the restraint? - females lay fewer eggs than they are capable

Reproductive restraint - English Swift Alternative explanation Why the restraint? Look at fledging success Clutch size% fledgingMean/nest

Wynne Edwards Group Selection - animals will behave in such a fashion as to sacrifice personal benefit for the benefit of the group (altruism) Difficult to explain genetically A - a gene that promotes altruism a - a gene that promotes selfishness A - can’t spread - contains automatic selection against itself

Wynne Edwards Difficult to explain genetically A - a gene that promotes altruism a - a gene that promotes selfishness A - can’t spread - contains automatic selection against itself p 2 + 2pq + q 2 = 1 Selection against any animal with’A’ = (1-s) P 2 (1-s) + 2pq(1-s) + q 2 = 1

Wynne Edwards Group Selection -reproductive restraint evolves if Benefit to group of altruism Reproductive advantage of being selfish

Group selection Rabbits introduced to Australia - 24 in about 1.5 billion Control with myxoma

Group selection Rabbits and Myxoma Facts/Assumptions 1. ‘Group’ = all the viruses in one rabbit 2. ‘virulence’ = lethality = r [reproductive rate] 3. Over time - virus has become less virulent 4. Transmission is by mosquitoes - so p [infection] is proportional to the lifespan of the rabbit

Group selection Rabbits and Myxoma Virulent formHigh reproduction (selfish) Lower probability of transmission Less virulent form Low reproduction (altruistic) Higher probability of transmission

Group selection Rabbits and Myxoma Group selection argument -less virulent = restrained reproduction = individual sacrifice for group survival -more virulent = higher indvidual success = group extinction Individual selection argument - high ‘r’ x low transmission < lower ‘r’ x high transmission

Social Behaviour Costs and Benefits Benefits 1. Protection from physical factors - Aggregations

Social Behaviour Costs and Benefits Benefits 2. Protection against predators a. Encounter Effect Grouped animals are more difficult to find

Social Behaviour Costs and Benefits Benefits 2. Protection against predators a. Encounter Effect predicted observed Encounter rate Colony size

Social Behaviour Costs and Benefits Benefits 2. Protection against predators b. Dilution Effect 1:91:1000’s

How do groups form? Hamilton - Geometry for the selfish herd Circular pond Colony of frogs Water snake Colony of frogs

How do groups form? Hamilton - Geometry for the selfish herd At same time each day, snake appears and frogs go to side of pond Colony of frogs

How do groups form? Hamilton - Geometry for the selfish herd Frogs are given the opportunity to move. How??? Colony of frogs Domain of danger

How do groups form? Hamilton - Geometry for the selfish herd Frogs are given the opportunity to move. How??? Colony of frogs Domain of danger

Social Behaviour Costs and Benefits Benefits 3. Mate searching

Social Behaviour Costs and Benefits Benefits 4. Foraging success

Social Behaviour Costs and Benefits Benefits 5. Resource defense

Social Behaviour Costs and Benefits Benefits 6. Division of Labour Termite Castes Queen Worker King Alate Soldier

Social Behaviour Costs and Benefits Benefits 7. Aiding relatives

Social Behaviour Costs and Benefits Benefits 8. Modifying the environment

Social Behaviour Costs and Benefits Costs 1. Increased competition Number of aggressive acs Colony size

Social Behaviour Costs and Benefits Costs 2. Increased disease and parasite rates Lice/ nestling Colony size

Social Behaviour Costs and Benefits Costs 3. Interference with reproduction

Social Behaviour -Why behave altruistically? W.D. Hamilton - Kin Selection Fitness has two components Direct - gained through personal reproduction Indirect - gained through reproduction of related individuals INCLUSIVE FITNESS

Social Behaviour -Why behave altrustically? Need to know the coefficient of relatedness r = the probability that two individuals possess the same allele due to common ancestry Parent/offspring0.5 Full siblings0.5 Half siblings0.25 Cousins0.125 [Aunt/Uncle]/[Niece/Nephew]0.25 Grandparent/grandchild0.25

Social Behaviour -Why behave altrustically? Hamilton’s rule Altruism will spread if B/C > 1/r B = benefit to recipient of altruist’s help C = cost to altruist r = coefficient of relatedness

Social Behaviour -Why behave altrustically? Examples?? Florida Scrub Jay

Social Behaviour -Why behave altrustically?

Typical Group Breeding Pair Helpers

Social Behaviour -Why behave altrustically? Reproductive success - benefits to breeding pair 1.62 young /nest 2.20 young /nest Helpers (any number)

Social Behaviour -Why behave altrustically? Reproductive success - benefits to helper 1.94 young /nest One Helper Helper success = = 0.32 x.5 (for relatedness) = 0.16

Social Behaviour -Why behave altrustically? Helper success = = 0.32 x.5 (for relatedness) = 0.16 From previous slide: Novice breeder success = 1.02 / nest x 0.5 = 0.51

Social Behaviour -Why behave altrustically? Helper success = 0.16 From previous slide: Novice breeder success = 0.51 Why sacrifice 2/3 of your own success by being a helper? Other costs in being a novice breeder 1. Survivorship 2. Being forced to marginal territories 3. Greater chance of taking over home territory