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Unformatted text preview: The Evolution of Eusociality in the Social Insects How did these strong social interactions evolve? In the case of halplodiploid Hymenoptera, one driving force may have been the high coefficient of relationship among the workers, which encouraged the evolution of altruism. Males are never workers in the Hymenoptera, presumably driven by their low coefficient of relatedness with other members of the nest. And if workers were to reproduce, they would have a coefficient of relatedness with their female offspring of only 0.5. It is therefore more beneficial for a worker to help raise a sister as a new queen than to have offspring of her own! The high coefficient of relatedness with the male offspring does not help, since the males contribute nothing to the workers’ inclusive fitness. x n male r = 1/2 r = 3/4 Diploid females r = 1/2 Female offspring Male offspring So strong is this effect that among bees, if workers do lay eggs, they are quickly eaten by other workers. Termites and the Naked Mole Rat But what about termites, which are eusocial and yet both males and females are diploid? And what about naked mole rats in Africa, subterranean mammals in which only one female reproduces and the others in a colony act as workers? It turns out that the colonies of these organisms are highly inbred, because the queen often mates with a related male. In both termites and naked mole rats, the reproductive females mate repeatedly with males in the same nest. The result is that the members have high coefficients of relationship with each other. Naked mole rats, which live in eastern and southern Africa and as far north as the Middle East, live in underground colonies. In the African species, though not those of the Middle East, only one female reproduces, and the other females and the males extend the burrows, find roots for food, and defend the burrows. The reproducing female prevents the other females from having babies through the use of sex pheromones that keep them from maturing sexually. Mole rats may have become eusocial because there is such a strong advantage to altruistic behavior on the part of the rats that defend the burrows. The mole rats of each group tend to be strongly related to each other because of inbreeding, so that an animal that sacrifices itself in defense of the reproductive female is sure to pass most of its own genes on. The same process may be taking place in termites, which are also diploid. The termites in a nest are also strongly related to each other because the queen tends to mate with males that are close relatives. Thus, haplodiploidy allows eusociality to evolve even in outbred organisms, while eusociality can only evolve in diploid organisms if they are inbred and live in colonies that must be defended, so that the benefits of altruistic behavior are very strong....
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This note was uploaded on 06/10/2010 for the course BILD 3 taught by Professor Wills during the Spring '07 term at UCSD.
- Spring '07