SPERM COMPETITION, MALE FITNESS, AND REPEATED MATING BY FEMALE DROSOPHILA MELANOGASTER.

Abstract

Females of many insect species store large numbers of after mating, and mate numerous times, sometimes before already stored is exhausted. The coincidence of these events results in sexual selection on males. Adaptations of a male which increase the probability that his sperm, and not the of some other male, is used by a female to inseminate her eggs will be favored by selection. Such adaptations may include behavioral and physiological characteristics of the male as well as competitive properties of the itself. Examples of such adaptations include 1) preand postcopulatory guarding behavior, 2) mating plugs, 3) chemical or physical characteristics of the ejaculate which reduce receptivity to remating, 4) displacement (i.e. the replacement at a subsequent mating of the stored of a previous mating), which could be effected either by the male during copulation or by some competitive aspect of the ejaculate, and 5) precedence (i.e. nonrandom use). Parker (1970), in his stimulating review of this subject, has used the term sperm to describe the selection pressures operating on males to produce these adaptations. Note that adaptations arising in response to these pressures are not restricted in their mode of operation to properties of the sperm, per se, but can involve any feature of reproductive biology affecting transfer or use. Studies of adaptations for competition in Drosophila have focused on displacement and, to a lesser extent, precedence and the effect of