Mating status, independent of size, influences lethal fighting in an entomopathogenic nematode

Abstract

Males of many species compete over access to females by physical contests. Previous experience of mating and the opportunity to mate with a female may influence the motivation of males to engage in contests and the outcome of such contests. Often, prior mating results in increased aggression and probability of success. This is mediated by the effects on the male's subjective evaluation of both the resource value (RV) and his own ability to acquire the resource (resource-holding potential, RHP). Moreover, having mated may also affect a male's actual fighting ability. In Steinernema nematodes, mated males paired with naïve males are more likely to win contests. Here we show that this advantage in mated males of Steinernema carpocapsae cannot be explained solely by the physical changes brought about by prior female contact, since males exposed to female pheromone alone developed sperm and increased in size like mated males but did not have the same advantage as them in contests with naïve males. Effects of mating on other components of RHP, such as skill or motivation, or on RV may explain the greater probability of mated males winning. We also show that mating had differential effects on the probability of a male initiating attack, depending on whether the opponent was a mated male (and thus ready to mate again) or naïve, consistent with the relative threat of the opponent as a competitor for copulations.