Ejaculate substances that affect female insect reproductive physiology and behavior: Honest or arbitrary traits?

Males of many insect species transfer, within the ejaculate, substances that render females sexually unreceptive and promote ovulation and oviposition. In this paper, I propose hypotheses for the evolutionary origin of these substances and discuss how selection may have modified them subsequently. Two hypotheses are considered. According to the handicap hypothesis, receptivity inhibition substances (RIS) and ovulation and oviposition stimulating substances (OSS) are used by females to evaluate the quality of the ejaculate received, the last being a function of the genetic or phenotypic quality of sperm, and of the nutritional or protective (to the female or her offspring) quality of its chemical constituents. This hypothesis predicts that RIS and OSS must be reliable indictors of ejaculate quality, reliability being the result of the high RIS/OSS production costs and specific chemical composition. The second hypothesis proposes that RIS/OSS are selected only in regard to their effectiveness as stimulators through Fisherʹs sexual selection runaway process. According to this hypothesis, RIS/OSS are not necessarily are reliable indicators of sperm or ejaculate chemical constituents quality (other than ability to stimulate), and must show a high species-specificity (rapid evolutionary divergence). Empirical evidence is reviewed, and the kind of information necessary to evaluate the relative importance of each hypothesis is indicated.