lecture 32 - adaptation and social behaviour Flashcards
What is the function of cooperative behaviour?
Consider cooperative hunting seen in killer whales. Killer whales participate in a behavior called wave washing, in which a pod of whales collectively creates waves to wash a prey species— typically a seal—off an iceberg. This behavior is collaborative, and it is clear why each individual participates. By itself, a single killer whale is incapable of generating a big enough wave, but, through cooperation, an individual can contribute to prey capture and gain some portion of the prey.
Perhaps the most prominent examples of this kind of behavior are sacrifices made by individuals apparently for the good of others. Formally, we describe an act of self-sacrifice as altruistic. Such acts seem to fly in the face of the natural selection, which posits that every individual competes for resources and mates to maximize its genetic contribution to the next generation.
Group selection provides a weak explanation of altruistic behavior. Group selection is the idea that natural selection operating on individuals is a less powerful force than selection that operates on groups. Although an attractive idea, group selection is probably not important in the evolution of altruism. Altruism under group selection is typically not an evolutionarily stable strategy, meaning that this kind of behavior can be readily driven to extinction by an alternative strategy or selfish strategy.
What is natural selection?
Entities reproduce There is inheritance There is variation =“descent with modification” Then Descendents will differ in survival and reproductive success (fitness) =“struggle for existence” More favourable characteristics spread.
The levels of selection debate: what are the entities?
For Darwin they were individuals but they could be Genes Groups Species Examples tell us gene selection works Theoretical issues: the speed of selection and coherence of entities.
What is Hamilton’s theory of kin selection?
A gene for altruism will spread if it is also in the individual which benefits from the altruism
r is Wright’s coefficient of relatedness which states how likely a gene in the actor is also in the recipient.
Altruism spreads if Br > C
Where B = benefits to recipient C=costs to actor.
Describe relatedness in social insects
The most famous cases of reproductive altruism occur in the insect group Hymenoptera, which includes ants, bees, and wasps. Many species of Hymenoptera are eusocial, meaning that they have overlapping generations in a nest, cooperative care of the young, and clear and consistent division of labor between reproducers (the queen of a honeybee colony) and nonreproducers (the workers). Often called social insects, these species are one of evolution’s most extraordinary success stories.
William Hamilton also noted that most Hymenoptera have an unusual mode of sex determination: Females (the queen and workers) are diploid, whereas males (drones) are haploid, produced from unfertilized eggs. As a result, the degree of relatedness, r, is higher for the sister–sister relationship (0.75) than for the mother–daughter one (0.5). Therefore, it makes more evolutionary sense, in terms of genetic representation in the next generation, for a worker to help her mother, the queen, to produce more sisters than for her to produce her own offspring.
What is reciprocal altruism?
Reciprocal altruism, whereby individuals exchange favors, is one way that altruism can evolve. This idea is perhaps best summarized as “You scratch my back, and I’ll scratch yours.” For this kind of behavior to work, individuals have to be able to recognize each other and remember previous interactions. If I did you a favor, I need to be able to recall who you are so that I can be sure that I get the return I expect.
An example can be seen in vampire bats. Bats returning from a successful feeding expedition often regurgitate blood to unsuccessful ones, on the expectation that the favor will be returned at a future date.
What is the ideal free distribution model?
Assumptions:
Patches vary in richness
Individuals choose the patch which maximizes their rate of food intake
There are no costs to movement and individuals are well informed
Individuals are equal competitors
Predictions:
Individuals will all have equal rates of food intake
Numbers in each patch are proportional to patch richness
The ideal free distribution model is an “optimization model”
individuals are predicted to behave in the way that
maximizes their fitness.
A fitness “currency” is assumed: rate of food intake
The model is also an Evolutionary Stable Strategy model (ESS model).
ESS models are optimization models where the fitness of any given behavioural choice depends on the choices other individuals make.
At the evolutionary endpoint (the ESS) no individual can do better by changing its behaviour.
How do you calculate food intake?
food input rate/ number of competitors
