Sex on Six Legs_ Lessons on Life, Love, and Language From the Insect World - Marlene Zuk [46]
Bob Trivers, an evolutionary biologist at Rutgers University, was interested in determining who "won" this potential conflict between the workers and the queen in the sex ratio of the social insects. With the assistance of Hope Hare, he painstakingly weighed the future reproductive individuals in the nests of a number of ant species. If the queen was in charge, as it were, and her reproductive interests are paramount, one expects that the weights—a reasonable gauge of investment—of the male and female future queens and males would be equal. If the workers prevailed, however, one expects a bigger investment in the young queens, by a factor of three, since the sisters are three times more closely related to each other than to their brothers. It turned out that the combined weight of the males in the nests was just about exactly one third of that of the future queens, supporting the idea that workers control the sex ratio of the colony. That discovery in turn means that insect societies, the most complex social systems on earth, are not dictatorships, but are controlled by a Machiavellian network of alliances and favors exchanged.
Incest and the Solution to Physics Envy
THIS successful application of theory to nature was only one of many triumphs of sex ratio theory as it applies to insects; arguably, the ability to predict with quantitative precision the relative numbers of males and females in an insect group is one of the most impressive confirmations of the operation of natural selection. Ecologists and evolutionary biologists often have to settle for qualitative predictions about the real world: we can say with assurance that a population will grow if more food is available, but exactly how much? Under most natural circumstances, too many other variables are at play to make precise predictions from such a biological hypothesis; the population's growth rate depends not only on food but also on, for example, the likelihood that disease will infect its members, or the abundance of predators in the neighborhood. This uncertainty has led to what people sometimes call "physics envy," the longing for the kind of mathematical confidence seen at least much of the time in the so-called hard sciences.
But physics envy can be cured by a dose of tiny parasitic wasps and an understanding of sex ratio theory. The wasps in question lay their eggs on other living insects, usually caterpillars or fly larvae, and the young wasps then develop inside this live food source until they are ready to become adults themselves. Just after the wasps become sexually mature, they mate, still on their host, and then the fertilized females go off to find victims of their own. Each caterpillar can support only a few females' offspring at most, which means that the young wasps find themselves in a very restricted universe in terms of dating opportunities. It's like going to a singles gathering with just your brothers and sisters and maybe the kids from the house across the street, and knowing you will have to find your lifetime mate from among only those individuals. Although inbreeding, or mating among relatives, has genetic penalties in many organisms, including humans, in the wasps it does not carry the same consequences, and they will mate quite unconcernedly with their siblings.
The mother wasp laying her eggs on the host has the same evolutionary problem as other organisms: how best to leave the most genes in the next generation. If she is the only individual parasitizing a particular caterpillar or maggot, she will get the most bang for her genetic buck by producing only enough males to fertilize their sisters, and making most of her offspring female. Making more males will only produce competition among them for the same mates, which won't do the mother wasp any good. The more additional females