Animal Social Behavior

Animal Social Behavior

Costs, Disadvantages Benefits, Advantages

Costs, Disadvantages competition… diseases, parasites degradation of environment increased conspicuousness… Benefits, Advantages competition… efficiency of foraging, predation… avoidance of predation opportunity to modify environment interaction with genetic relatives recall that “family” is one of the levels of biological organization

Animal Social Behavior Is family important?

Animal Social Behavior How is genetic relatedness determined?

female parent C1C2

female parent C1C2 male parent C3C4

female parent C1C2 male parent C3C4 “diplodiploidy”

female parent C1C2 male parent C3C4 possible gametes: C1 C2 C3 C4

female parent C1C2 male parent C3C4 possible offspring: C1C3 C2C3 C1C4 C2C4

female parent C1C2 male parent C3C4 What proportion of genes do parents share with their offspring? possible offspring: C1C3 C2C3 C1C4 C2C4

female parent C1C2 male parent C3C4 possible offspring: C1C3 C2C3 C1C4 C2C4 gender doesn’t matter…

female parent C1C2 male parent C3C4 possible offspring: C1C3 C2C3 C1C4 C2C4 what about siblings?

female parent C1C2 male parent C3C4 possible offspring: C1C3 C2C3 C1C4 C2C4 Take any particular offspring… C2C3

female parent C1C2 male parent C3C4 possible offspring: C1C3 C2C3 C1C4 C2C4 Take any particular offspring… C2C3 What proportion of genes are shared with its siblings?

female parent C1C2 male parent C3C4 possible offspring: C1C3 C2C3 C1C4 C2C4 Take any particular offspring… C2C3 What proportion of genes are shared with its siblings? C1C3 C2C3 C1C4 C2C4 0.5

female parent C1C2 male parent C3C4 possible offspring: C1C3 C2C3 C1C4 C2C4 Take any particular offspring… C2C3 What proportion of genes are shared with its siblings? C1C3 C2C3 C1C4 C2C4

female parent C1C2 male parent C3C4 possible offspring: C1C3 C2C3 C1C4 C2C4 Take any particular offspring… C2C3 What proportion of genes are shared with its siblings? C1C3 C2C3 C1C4 C2C4 What is the average proportion of genes shared by common descent by siblings?

The average proportion of genes shared by common descent between any two individuals is the “coefficient of genetic relatedness” and is symbolized “r”

The average proportion of genes shared by common descent between any two individuals is the “coefficient of genetic relatedness” and is symbolized “r” In diplodiploid species: parents - offspring, r = 0.5 siblings, r = 0.5 grandparents and grandchildren, r = 0.25

The average proportion of genes shared by common descent between any two individuals is the “coefficient of genetic relatedness” and is symbolized “r” In diplodiploid species: parents - offspring, r = 0.5 siblings, r = 0.5 grandparents and grandchildren, r = 0.25 Aunts/uncles and nieces/nephews? Cousins?

siblings Becky -- Steve Charles -- Deborah Chris Jeff Rachel Lauren

0.5 Becky -- Steve Charles -- Deborah Chris Jeff Rachel Lauren 0.5 0.5 Aunts/uncles with nieces/nephews, r = 0.25 (0.5 x 0.5) first cousins, r = (0.5 x 0.5 x 0.5)

0.5 Becky -- Steve Charles -- Deborah Chris Jeff Rachel Lauren Lorna Elanor 0.5 0.5 0.5 “Descendant kin” = those in direct lines of descent (parents, offspring, grandparents, grandoffspring) “Collateral kin” = relatives but not descendants or ancestors (siblings, aunts/uncles, nieces/nephews, cousins)

0.5 Becky -- Steve Charles -- Deborah Chris Jeff Rachel Lauren Lorna Elanor 0.5 0.5 0.5 How much did my fitness increase when Ella was born?

0.5 Becky -- Steve Charles -- Deborah Chris Jeff Rachel Lauren Lorna Elanor 0.5 0.5 0.5 How much did my fitness increase when Ella was born? This is “direct fitness” (r = 0.25)

0.5 Becky -- Steve Charles -- Deborah Chris Jeff Rachel Lauren Lorna Elanor 0.5 0.5 0.5 How much did my fitness increase when Ella was born? This is “direct fitness” (r = 0.25) How much did Jeff’s fitness increase when Ella was born?

0.5 Becky -- Steve Charles -- Deborah Chris Jeff Rachel Lauren Lorna Elanor 0.5 0.5 0.5 How much did my fitness increase when Ella was born? This is “direct fitness” (r = 0.25) How much did Jeff’s fitness increase when Ella was born? This is “indirect fitness” (r = 0.25)

0.5 Becky -- Steve Charles -- Deborah Chris Jeff Rachel Lauren Lorna Elanor 0.5 0.5 0.5 How much did my fitness increase when Ella was born? This is “direct fitness” (r = 0.25) How much did Jeff’s fitness increase when Ella was born? This is “indirect fitness” (r = 0.25) How much did Charles’ fitness increase when Ella was born? This is also “indirect fitness” (r = 0.125)

0.5 Becky -- Steve Charles -- Deborah Chris Jeff Rachel Lauren Lorna Elanor 0.5 0.5 0.5 The combination of “direct fitness” and “indirect fitness” for any particular individual is that individual’s “inclusive fitness”

The combination of “direct fitness” and “indirect fitness” for any particular individual is that individual’s “inclusive fitness” Selection that acts on individuals so that they behave in ways that increase their inclusive fitness is called “indirect selection”

The combination of “direct fitness” and “indirect fitness” for any particular individual is that individual’s “inclusive fitness” Selection that acts on individuals so that they behave in ways that increase their inclusive fitness is called “indirect selection” Darwin got it right when he wrote that “…selection may be applied to the family as well as to the individual…”

Heritable variation (among families, in behaviors that promote inclusive fitness) combined with differential RS (among families) leads to the spread of characteristics (that increase inclusive fitness) through populations adaptive behaviors may evolve due to the action of indirect selection

What kinds of behaviors might evolve through the action of indirect selection? What kinds of behaviors increase the inclusive fitness of an individual and thus the overall fitness of the family? Behaviors that appear to benefit the fitness of “recipient” individuals at a cost to the fitness of the “donor” individual… …are called “altruism” Most behaviors that appear to be altruistic are thought to have evolved through the action of indirect selection

What is the alternative to altruism? “Selfishness” is behavior that promote an individual’s RS, without worrying about the effect of that behavior on the RS of other individuals Is selfishness or altruism more likely to evolve?

Animal Social Behavior What is the effect of indirect selection?

This is why we need a special explanation for altruistic behavior - Darwin recognized this need S S S S S

Under what conditions (ecological, genetic) is altruism most likely to evolve?

Animal Social Behavior

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