Spermatophore allocation strategy over successive matings in the bushcricket Isophya sikorai (Orthoptera Phaneropterinae)

Abstract

During mating, male bushcrickets transfer edible spermatophores that consist of a large sperm-free spermatophylax and a sperm-containing ampulla. The effect of consecutive matings on nuptial gift and sperm numbers in the bushcricket Isophya sikorai was examined. Males and females differed in body weight and mating history influenced their weight. Males differed in spermatophore weight, as well as the weights of spermatophylax and ampulla. Spermatophore (spermatophylax+ampulla) and spermatophylax weight of I. sikorai increased with male body weight, but not with ampulla weight. Male age had a significant effect on sperm number, with older males producing more sperm. Female weight but not mating number of female had a significant effect on spermatophore weight. Males increased the size of the spermatophylax and sperm number when presented with larger females, but they did not adjust their ampulla weight. Male age affected spermatophylax weight when mating with heavier females. Males reached their maximal absolute sperm number point at about middle age of their mating period due to an age-dependent shift in covariation between the ampulla and spermatophylax weight and ampulla size increases over a longer period. We conclude that production of a spermatophore and its components is costly, therefore males should strategically adjust their spermatophore components among mating opportunities. Female quality is an important predictor in searching males, and those males transfer significantly larger spermatophore and ejaculates to higher quality (heavier) females. Briefly, this study suggest that male I. sikorai strategically allocate spermatophore size and sperm number with respect to various factors such as his age, sperm competition and female size in a multiple mating system.