10. Cooperation and Helping

Inclusive Fitness• Direct Fitness (Individual Fitness): personal

reproductive success measured as the number of offspring that survive and reproduce

• Indirect Fitness: reproductive success of individuals that share genes with the donor

• Inclusive Fitness = Direct Fitness + Indirect fitness: the total genetic contribution of an individual to the next generation

Coefficient of relatedness

Coefficient of relatedness ( r): proportion of alleles shared between two individuals as a result of common descent (ancestry)

Relationship Average r coefficient

• Parent-offspring 0.5 (1/2)

• Full siblings 0.5 (1/2)

• Half siblings 0.25 (1/4)

• Grandparent-Grandchild 0.25 (1/4)

• Aunt or uncle - niece or nephew 0.25 (1/4)

• First cousins 0.125 (1/8)

Mitosis Meiosis

Parents

gametes (1n)

How are traits transferred to offspring?

Offspring

gametes (1n)

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Calculating Inclusive Fitness

r = coefficient of relatednessN = number of offspring

Hamilton’s rule

Br > C

The altruistic/helpful behaviour will spread in the population if the NET benefit to the recipient x coefficient of relatedness is greater than the cost suffered by the altruist

Cooperative breeding• In some species, younger individuals forego their own

reproduction to help others rear offspring

White-fronted bee-eaters

Cooperation among Florida scrub jays (Aphelocoma coerulescens)

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The relationship between the number of Florida scrub jay helpersand the breeding success of the experienced parents. Helpers do notincrease the number of eggs laid.They do, however, increase the chances that the eggs will hatch and that the young will surviveto become independent. (data from Woolfenden 1975)

The relationship between the number of blackbacked jackal helpersand the number of the pups. (Moehlman 1979)

Cooperation among blackbacked jackals (Canis mesomelas)

Eusociality

Type of social organization of animals

Reproductive division of labour (reproductive and nonreproductive castes)

Cooperation in the care for young An overlap between generations

Hymenoptera:ants, bees and wasps

S

C E

Isoptera - all termites

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Ants show caste polymorphism

Female parentDiploid

Male parentHaploid

Male offspringHaploid

Female offspringDiploid

Haplodiploidy in eusocial insects

The genetic contribution of a male and female of a haplodiploid species.The maternal contribution is only half of the female offspring’s genes.Since the mother is diploid, sisters have 25% of their genes in common throughtheir mother’s gametes.The father is haploid, so his sperm are all identical.As a result, sisters have 50% of their genes in common through their father’s gametes.Male offspring are haploid. Each male’s entire set of genes comes from his mother.Thus, the average degree of relationship among brothers is 50%.

Eusociality in the naked mole-rat

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Naked mole rats

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Reciprocal Altruism (reciprocity)

An action by an individual (the donor) that helpsanother individual (the recipient), and that is subsequentlyrepaid by the recipient.

Conditions necessary for reciprocal altruism to evolve:Opportunities for repaymentIndividual recognitionDiscrimination against cheatersBenefit to the recipient > cost to the actor

Prisoner’s Dilemma