A clear-cut difference in nuptial strategies may shape sperm traits in two paper wasps

Spermatozoa vary in quantity, quality and design across species and individuals. Here, we reported the first detailed analysis of sperm traits in two primitively eusocial paper wasps, Polistes dominula and Polistes gallicus, which differ in their nuptial strategies and body size as follows: lek-territoriality of the large P. dominula males, defending exclusive territories at landmarks; scramble competition of the small P. gallicus, where serial mating may occur because males interfere with rivals and replace them during copulation. We compared the number, viability, and length of sperm, and its coefficient of variation, between these sympatric paper wasps patrolling and marking the same landmarks during the same summer: a good opportunity to analyse sperm across species while controlling for environmental variables. Spermatozoa were more numerous and longer in P. dominula than in P. gallicus males. Viability was similar in both species and positively covaried with male body size. Intra-male variation in sperm length was significantly reduced in P. gallicus, as predicted in the case of selection for an optimal sperm design. We hypothesized that precopulatory sexual selection (lek-territoriality vs. scramble competition) may affect sperm traits.