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Evolution 22: Kin Selection

Evolution 22: Kin Selection. Interactions and Fitness. Mutualism (Cooperation)…fitness gains for both participants Altruism …Individual instigating the action pays a fitness cost and the receiver benefits Selfishness …The actor gains and the recipient loses

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Evolution 22: Kin Selection

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  1. Evolution 22: Kin Selection

  2. Interactions and Fitness • Mutualism (Cooperation)…fitness gains for both participants • Altruism…Individual instigating the action pays a fitness cost and the receiver benefits • Selfishness…The actor gains and the recipient loses • Spite…fitness losses for both participants….never witnessed in nature

  3. Why spite has not evolved? • Loss for the actor and recipient would be severely selected against! • However, wouldn’t the cost be worth it if the actor imposes a more severe blow to the fitness of the recipient than the damage to their own fitness? • However, consider the fitness of a third party. They neither loose fitness doling out those blows or receiving them!

  4. How can altruism evolve? • Darwin had trouble dealing with this. He considered it potentially fatal to his theory of evolution by natural selection • He did hint that selection could act on traits that promote the fitness of close relatives at the expense of the owner of the trait

  5. Inclusive Fitness • Hamilton developed the concept where inclusive fitness=direct and indirect fitness • Direct fitness results from personal reproduction • Inclusive fitness results from additional reproductions by relatives as the result of the individuals actions

  6. How does indirect fitness evolve • We have a coefficient of relatedness, r (0-1). It is similar to F…the probability that homologous alleles in the same individual are identical by descent • Hamiltons rule states that altruistic behaviors will spread if Br-C>0, where B is the benefit to the recipient and C is the cost to the actor. • The altruistic behavior will spread if the benefit to the recipient is great, the relatedness is high, and cost to the actor is low

  7. Example of Altruism • Belding’s ground squirrels • Sherman observed them for 14 years and discovered: • When they see hawks, they whistle…this results in captures 2 % of the time by the hawk • If they do not whistle, this results in captures 28% of the time • If they spot a mammal, they trill • Trill results in captures 8% of the time • Not trilling results in captures 4% of the time • Whistling is selfish, trills are altruistic

  8. Females are more likely to trill, why?

  9. Females are more likely to trill with relatives in earshot

  10. Not as inclined to help distant relatives

  11. Helpers in bird families • Young that are old enough to breed often help their parents raise sibs or half-sibs instead of breeding themselves • Happens more when suitable nest sites for the young are difficult to be found (poor resources) • Coef.of relatedness predicts how much white-fronted bee eaters help their kin

  12. Cannibalistic tadpoles/salamanders • Pfennig put cannibalistic spadefoot frog tadpoles in tanks with ominivorous sib or non-kin • Only 6/28 ate their kin • With tiger salamanders, Pfennig did the same • If degree of relatedness is 1/2, and B is the benefit of the kin not being eaten, and C is the cost to the cannibal for not eating, then we see: • Sibs of discriminating cannibals were 2x likely to survive, thus B=2 • Cannibals suffer very little fitness loss by missing a meal (age and size at metamorphosis) • So, B(1/2)-C=1. Discriminating kin when you are a cannibal should evolve!!!!

  13. Cannibals!!!!! Ambystoma tigrinum Donner Party

  14. Altruistic Sperm • European field mice engage in sperm competition • Sperm from one individual cooperate…they use hooks to grab one another and make a train • This train will move twice as fast as single sperm • However, the train must break up prior to fertilizing an egg • They can only break apart by releasing the same enzyme that will fertilize the egg • By releasing the enzymes prior to egg fertilization, many sperm sacrifice themselves on behalf of the sibs that actual fertilize the egg!!!

  15. Avoiding sacrifice for non-kin • Female coots (a bird) will parasitize the nests of other female coots…they lay their eggs in other’s nests • Only 1/2 of a clutch of 8 will survive anyhow • Selection should provide a mechanism to defend against parasitism • Some can recognize other coots eggs and discard them (43%) • On average they lay 8 eggs • They will discard the parasites egg and lay their own 8 • It shows they can count!

  16. Greenbeard alleles • If altruistic alleles were recognizable (say by a phenotypic trait like a greenbeard), what do you think the bearer of that trait would do in the presence of another individual with that trait? • The gene makes you act altruistically and helps you recognize it in others! • The gene would spread because all parties with the gene would recognize one another and help one another! • Not common in nature

  17. Eusociality • Social insects engage in the most extreme form of altruism • Bees, wasps and ants have social morphs that do not breed • Defined: • 1. Parents and offspring generations overlap • 2.Cooperative brood care • 3.Specialized castes of nonreproductive individuals

  18. Haplopolyploidy and Hymonoptera • Bees have worker, soldier and reproductive castes • Males are haploid and females are diploid…haplopolyploidy…females are more closely related to their sibs than their own offspring • They share all of their genes they inherit from their father (1x1/2) and half the genes they inherit from their mother (the queen) (1/2x1/2)….1/2+1/4=3/4 related to sibs!!! • Thus females will maximize their fitness by working to help their sibs than reproducing themselves!!! • They are related to brothers by r=1/4

  19. Testing the hypothesis! • Females are workers and have r=3/4 with sisters and r=1/4 with brothers. So, in the hive, they should favor the membership to be 3/4 / 1/4 =3:1 • Queens are equally related to sons and daughters…they should favor a 1:1 ratio • Queens lay equal sex ratio of eggs • Who wins with respect to desired sex ratio…workers or queens? • Remember, the workers tend the eggs!! • The workers can determine the sex of the eggs and selectively destroy males…thus the result is a 3:1 ratio

  20. Haplopolyploidy effects the evolution of Eusociality, but is not the most important • 1) Incorrect generalization: Female workers all have the same father…not so, thus r goes down to 1/3 • 2) Sometimes more than one queen will found a nest, thus r=0 for some • 3) Not all eusocial insects are haplodiploid and vice versa • Possibly, eusociality evolved to make the best out of a bad situation (like birds) • Breeding in isolation has high costs…taking care of young, predators etc….

  21. Eusociality in Mammals!!!!

  22. Naked Mole Rats • Neither moles nor rats • Live underground in extensive colonies of 70-80 members, constructing tunnels • All young are produced by a single queen and 2-3 males • Workers tend the young, dig tunnels, or defend tunnels • Highest inbred animals documented (r=0.81) • The reason for eusociality • 85% of matings between parents and offspring or full sibs • Conflicts do arise b/c workers would still be more related to their own offspring than sibs • However, queens make maintain control by dominance and physical punishment!!!

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