Kin selection

actor

+ -

+ cooperative altruistic

- selfish spiteful

recipient

Individual interaction behaviors

altruism presented a “special difficulty, which at first appeared to me insuperable, and actually fatal to my whole theory.”

Darwin 1859

‘Altruisitc’ interactions

Manipulation

Individual advantage

Reciprocal altruism

Kin selection

Manipulation

nest parasitism

brown headed cowbird

Individual advantage

fish schooling

selfish herd

Reciprocal altruism can evolve only under a restricted set of conditions

A will help B, if B will help A in the future

Need:-repeated interactions

-individual recognition

Reciprocal altruism

grooming

Vampire bats reciprocate by sharing blood meals.

They usually share with close relatives or non-relatives who are roostmates and may later reciprocate

Reciprocal altruism

Most alleles favored by kin selection rise to high frequency by inducing altruism toward individuals likely to be carrying copies of the same allele

Selection can favor making sacrifices for kin; it should also favor avoiding sacrifices for non-kin

Kin selection

Inclusive fitness consists of direct fitness due to personal reproduction and indirect fitness due to additional reproduction by relatives

Inclusive fitness = direct fitness + indirect fitness

Behavior that results in indirect fitness gains is favored by kin selection

Inclusive fitness

0.5

Coefficient of relatedness

parent-child

0.5

0.50.50.5

0.25 + 0.25 = 0.5full siblings

0.50.5

0.25half siblings

0.5

0.5

0.25grandparent - grandchild0.5

0.50.5

0.5 x 0.5 x 0.5 = 0.125cousins

Helpers gain indirect fitness benefits because they are very closely related to their siblings

Helpers at the nest

Florida scrub jay

Helpers at the nest

White-fronted bee-eater

Helpers at the nest

White-fronted bee-eater

Alarm calling

Belding’s ground squirrels

Alarm calling

Belding’s ground squirrels

Alarm calling

Meerkat sentinels

Science, June 04 1999, 284: 1585

Cannibalistic tadpoles

Spadefoot toad tadpolesomnivorous morphcarnivorous morph

Parents maximize their fitness by investing in all of their offspring equally

Offspring, in contrast, maximize their fitness by receiving more parental investment than their siblings

Siblicide may increase the fitness of parents as well as the siblicidal offspring if the offspring that is killed is likely to die anyway

Siblicide

Siblicide - adelphophagy

Sand tiger shark

Intra-uterine embryonic cannibalism

Eusociality

Eusociality

3 characteristics:

overlap in generations between parents & offspring

cooperative brood care

specialized castes of non-reproductive individuals

In haplodiploid species females are more closely related to their sisters than they are to their own offspring

(0.5 x 0.5) + (1 x 0.5) = 0.75

sisters

10.5

motherdiploid

fatherhaploid

(0.5 x 0.5) = 0.25

brothers

Eusociality

Eusociality

Eusociality

Eusociality

haplodiploidy does not completely explain the evolution of eusociality

many eusocial species are not haplodiploid

many haplodiploid species are not eusocial

Eusociality

naked mole rats