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Kin selection. Individual interaction behaviors. actor. recipient. 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
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Individual interaction behaviors actor recipient
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
0.5 0.5 0.5 0.25 0.5 half siblings 0.25 0.5 grandparent - grandchild 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.25 + 0.25 = 0.5 0.5 x 0.5 x 0.5 = 0.125 full siblings cousins Coefficient of relatedness parent-child
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 3 characteristics: overlap in generations between parents & offspring cooperative brood care specialized castes of non-reproductive individuals
mother diploid father haploid 0.5 1 Eusociality 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 (0.5 x 0.5) = 0.25 sisters brothers
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