EJACULATE SUBSTANCES THAT AFFECT FEMALE INSECT REPRODUCTIVE PHYSIOLOGY AND BEHAVIOR - HONEST OR ARBITRARY TRAITS

Males of many insect species transfer, within the ejaculate, substance s that render females sexually unreceptive and promote ovulation and o viposition. In this paper, I propose hypotheses for the evolutionary o rigin of these substances and discuss how selection may have modified them subsequently. Two hypotheses are considered. According to the han dicap hypothesis, receptivity inhibition substances (RIS) and ovulatio n and oviposition stimulating substances (OSS) are used by females to evaluate the quality of the ejaculate received, the last being a funct ion of the genetic or phenotypic quality of sperm, and of the nutritio nal or protective (to the female or her offspring) quality of its chem ical constituents. This hypothesis predicts that RIS and OSS must be r eliable indictors of ejaculate quality, reliability being the result o f the high RIS/OSS production costs and specific chemical composition. The second hypothesis proposes that RIS/OSS are selected only in rega rd to their effectiveness as stimulators through Fisher's sexual selec tion runaway process. According to this hypothesis, RIS/OSS are not ne cessarily are reliable indicators of sperm or ejaculate chemical const ituents quality (other than ability to stimulate), and must show a hig h species-specificity (rapid evolutionary divergence). Empirical evide nce is reviewed, and the kind of information necessary to evaluate the relative importance of each hypothesis is indicated.