FEMALE RESISTANCE AND MATING OUTCOMES IN A STREAM-DWELLING ISOPOD: EFFECTS OF MALE ENERGY RESERVES AND MATING HISTORY

Abstract

Abstract In the stream-dwelling isopod, Lirceus fontinalis, conspicuous mating contests occur between males and females prior to pair formation. Our previous work has shown that female resistance during contests determines contest outcomes. Here we examined whether female resistance could act as a mechanism of choice in which females discriminate against males with low energy (glycogen) reserves. We manipulated male glycogen levels by chasing males around a race-track then exposed females to males that differed in glycogen levels. We found that high-glycogen males were more successful than low-glycogen males and that this effect appeared to be due to increased female resistance towards low-glycogen males. We then examined one potential benefit to females of energy-based mate discrimination. In L. fontinalis, male mating history and levels of glycogen reserves are correlated, i.e. recently mated males are glycogen-depleted due to energy costs associated with mating. We examined whether recently mated males were also costly mates, and thus should be avoided by females. We quantified the relationship between male mating history and female fertilization success and found that females suffered an 18% reduction in fertilization success by mating with a male that had recently inseminated another female. We propose that female resistance could act as a mechanism of choice in which males with low energy reserves are avoided and that one benefit of this discrimination is that females increase fertilization success be avoiding males that have recently mated.