Exercise 13 Key
In naked mole rats, when the existing queen dies, she is replaced by one of the senior female workers. Often, however, there are several such individuals, all of which are quite closely related. Nevertheless, a queen’s death is often followed by a period of intense fighting between these female workers, with the outcome usually death for the losers. Explain why altruism is lacking, and such intense aggression occurs instead, in a system where the combatants are highly related and exhibit extreme cooperation most of the time.
Use Hamilton’s Rule and evaluate each of the main variables in this new situation. The death of the queen changes one key variable in Hamilton's rule. When the queen is alive, the female workers cannot breed on their own (very low C) and can help raise very close relatives (high rB). Hence altruism is favored. When the queen dies, each female now has an opportunity to breed. Being altruistic to a sister (letting her breed) now has a very high cost (C). Any allele that produced non-aggressiveness in this situation could only be favored if it increased the fitness of relatives by the equivalent number of self-produced offspring (in this case, without inbreeding, that would be two nieces or nephews for every offspring). This is extremely unlikely, because even if the winner is a relative, she is unlikely to have higher reproduction than the focal individual would. Therefore the cost of being non-aggressive is hypothesized to be substantially higher than any benefits. Indeed, the benefit of breeding may be so high (and therefore C for being altruistic may be so high), that females may be favored to risk death in order to take advantage of the opportunity.