Social behavior can be understood by asking how it contributes to the fitness of all the individuals involved. Asymmetry between the sexes in parental investment is a key factor in the evolution of mating systems. According to the theory of kin selection, an individual can increase its fitness by helping related individuals with whom it shares alleles. In extreme cases, kin selection has given rise to eusociality.
learning outcomes
You should be able to:
Apply concepts of fitness to explain the evolution of social behaviors related to reproduction.
Explain how haplodiploidy relates to eusociality.
Identify costs and benefits of social behaviors.
Explain the selective pressures that favor an individual being a helper at the nest rather than engaging in reproduction.
Selection will favor an individual helping its parents raise offspring rather than breeding itself when the chances of its own successful breeding are very low. Raising several brothers or sisters contributes more to an individual’s inclusive fitness than not raising one’s own offspring.
What is the relationship between haplodiploid sex determination and the evolution of eusociality in ants, wasps, and bees?
Because of the haplodiploid mechanism of sex determination in hymenopterans, sisters share 75 percent of their genes, but parents and offspring share only 50 percent. The unit of reproductive success in eusocial insects is the colony formed around a queen. By helping her mother raise sisters, it is likely that a worker will share 75 percent of her genes with a new queen, but if the new queen were one of her offspring, the worker would share only 50 percent of her genes.
Many species of small birds respond to the presence of a much larger predator by joining together to mob the predator and drive it off. What do you see as the risks and benefits of this behavior, and what hypotheses could you propose about the individuals taking part in an incidence of mobbing behavior?
The main risk of mobbing a potential predator is the possibility of being attacked and injured by the predator. A benefit of mobbing is that the predator is distracted from focusing on specific prey, such as the eggs or nestlings of the mobbers. The mobbing also warns others in the population of the presence of a predator. Of course, the major benefit is that the predator is driven away. Hypotheses about individuals taking part in mobbing would include that they are likely to be related, that they are more likely to participate if they have nestlings, and that monogamous males are more likely to join in mobbing than are promiscuous males.