SEXUALLY ANTAGONISTIC MALE ADAPTATION TRIGGERED BY EXPERIMENTAL ARREST OF FEMALE EVOLUTION

EACH sex is part of the environment of the other sex. This may lead to perpetual coevolution between the sexes, when adaptation by one sex r educes fitness of the other. Indirect evidence comes from experiments with Drosophila melanogaster indicating that seminal fluid reduces the competitive ability of sperm from other males, thereby increasing mal e fitness(1,2). It also reduces a female's propensity to remate and in creases her egg-laying rate(3). In contrast to these benefits to males , seminal fluid has substantial toxic side effects in females, with in creasing quantity leading to decreasing female survival(4,5). Here I s how that when female D. melanogaster are experimentally prevented from coevolving with males, males rapidly adapt to the static female pheno type. This male adaptation leads to a reduction in female survivorship , which is mediated by an increased rate of remating and increased tox icity of seminal fluid.