Transcript Document
Kin selection Individual interaction behaviors actor + - + cooperative altruistic - selfish recipient spiteful 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 A will help B, if B will help A in the future Reciprocal altruism can evolve only under a restricted set of conditions Need: -repeated interactions -individual recognition grooming Reciprocal altruism Vampire bats reciprocate by sharing blood meals. They usually share with close relatives or non-relatives who are roostmates and may later reciprocate Kin selection Selection can favor making sacrifices for kin; it should also favor avoiding sacrifices for non-kin Most alleles favored by kin selection rise to high frequency by inducing altruism toward individuals likely to be carrying copies of the same allele Inclusive fitness 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 Coefficient of relatedness 0.5 0.5 0.5 parent-child 0.25 half siblings 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.25 grandparent grandchild 0.5 0.5 0.25 + 0.25 = 0.5 full siblings 0.5 x 0.5 x 0.5 = 0.125 cousins Helpers at the nest Helpers gain indirect fitness benefits because they are very closely related to their siblings 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 tadpoles omnivorous morph carnivorous 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 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 - 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 Eusociality In haplodiploid species females are more closely related to their sisters than they are to their own offspring mother father diploid haploid 0.5 1 (0.5 x 0.5) + (1 x 0.5) = 0.75 sisters (0.5 x 0.5) = 0.25 brothers 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