Sexual dimorphic traits and male fertility in a paper wasp

Females of many social Hymenoptera commit their reproductive potential to a single male: they mate once and never re-mate. Sexual selection theory predicts that under this regime female pre-copulatory mate choice is critical. The targets of female choice, male secondary sexual traits, should convey information about the functional fertility of the male, Here, we evaluated semen quality and its correlates in the paper wasp Polistes dominula, a monandric species with a lek-based mating system. The main goal of this study was to test if sperm viability and total sperm number co-varied with sex-dimorphic abdominal spots, body size and parasite infection by Xenos vesparum. Surprisingly, male superior fertility was not predicted by attractive sexual traits such as round little spots and large body size. We also found no effect of the parasite on male fertility, sexual ornamentation or body size. We only found that sperm viability was positively associated to sperm number. Moreover, there was evidence of a counter- intuitive relation between irregular large spots – not sexually attractive – and large body size of dominant successful males. Overall, our results suggest a condition dependent trade-off between body size and costly sexual signals