Copulation duration in the soldier fly: the roles of cryptic male choice and sperm competition risk

In most animal species, females invest more in reproduction than males do and are therefore expected to be the choosier sex. However, male choice is also expected to occur whenever there is sufficient variation in female quality and male mating effort is high. Postcopulatory or "cryptic" male choice is defined as variation in the amount of resources males allocate to females of varying quality. The soldier fly Merosargus cingulatus exhibits significant variation in copulation duration. This variation in mating effort may be a consequence of cryptic male choice, although other processes such as sperm competition may also play a role. In this study, I manipulated factors associated with the risk of sperm competition (male density) and varying mate quality (female size) to determine whether these factors affected male mating effort. I found direct evidence that male M. cingulatus can control copulation duration. Copulations were longer when male density was high, which support the hypothesis that males increase copulation duration when there is a high risk of sperm competition. In addition, copulation duration was longer when males mated with larger more fecund females, which supports the hypothesis of cryptic male choice. Copyright 2011, Oxford University Press.