Lecture 16

• Altruism


  In Evolutionary Biology, altruism means: Behaviour that decreases the direct fitness of the actor and increases the direct fitness of the recipient

  
• Altruistic individuals should have a selective disadvantage and genes for altruism should not spread

  
• There are four basic kinds of social interaction, defined by the direct fitness outcome for the actor and the recipient
• Group selection


  Before the mid-1960s, altruism was explained using the theory of group selection: Populations that contain many selfish individuals may be more likely to go extinct (e.g., if they exhaust their food supply), Only groups containing altruists would spread and persist
• The problem with group selection

  • Evolution does not operate for the "good of the species" or "for the good of the group", Within a group of altruists, a selfish mutant (or migrant) who took advantage of the altruists would have a huge selective advantage, The mutant alleles for selfishness would spread rapidly and soon the entire group would be selfish
• Inclusive fitness


  An individual's total fitness; the sum of the individual's direct and indirect fitness
• Direct fitness


  One's own reproductive output
• Indirect fitness


  Reproductive output of one's relatives (who share alleles with oneself), which can be enhanced by one's altruistic behaviour

  
• Kin selection


  Natural selection based on gains in inclusive fitness
• Hamilton's rule


  Kin selection will favour altruistic behaviour when the cost to the actor (C) is less than the benefit to the recipient (B) multiplied by the relatedness between the actor and recipient (r)
• Relatedness is the probability that a pair of alleles drawn from two individuals are identical by descent
• Relatedness coefficient (r)


  Offspring-parent: 0.5, Full sibs: 0.5, Half sibs: 0.25, Offspring-grandparent: 0.25, First cousins: 0.125
• Parental care


  Parental care is expected to evolve only if its fitness benefit exceeds its fitness cost
• Parent-offspring conflict


  Offspring often want to extract more resources from parents than parents are willing to give
• Weaning conflict


  One of the most familiar forms of parent-offspring conflict, where mothers generally want to stop nursing before offspring do, and offspring try to force them to continue
• The most extreme altruism occurs in eusocial animals
• Eusociality


  Only one/few individuals breed, others are sterile and help to rear offspring and to police interactions
• Eusociality in hymenopterans


  • Haplodiploidy may predispose hymenopterans to eusociality, In a colony with a singly mated queen, females are more closely related to their sisters (r = 0.75) than they would be to their own daughters (r = 0.5), The best way for a female to get more of her genes into the next generation is to forego reproduction and help her mother (the queen) create more sisters
• Reciprocal altruism


  It can be advantageous to help another individual if there is a high probability of receiving aid from that individual in the future
• Reciprocal altruism


  • Vampire bats regurgitate blood to feed hungry roost-mates, Roosting bats that fail to reciprocate are punished by expulsion from the group
• Other reasons for cooperation

  • Being in a group may provide protection from predators or harsh environment, May be able to garner more resources as a group than as individual, May be able to take over territory after original owner dies
• Individuals may help increase fitness of others not because it is adaptive, but because they are being manipulated
• Manipulation


  • Brood parasitism occurs in many species of birds, Female sneakily lays eggs in nest of other female, who then takes care of both sets of young, Cuckoldry is same situation except from the male point of view