The strength of postcopulatory sexual selection within natural populations of field crickets

Sperm competition and cryptic female choice are likely to exert strong postcopulatory sexual selection and may amplify or ameliorate selection acting via male mating success. However, relatively few studies have estimated the potential strength of postcopulatory sexual selection acting within natural populations. Field crickets in the genus Teleogryllus have been used extensively as laboratory models to study the evolution of polyandry, and the mechanisms of sperm competition and cryptic female choice. However, we have no knowledge of the extent of multiple mating or patterns of sperm utilization in natural populations of these crickets. We used microsatellite loci to examine the strength of postcopulatory sexual selection in Teleogryllus oceanicus and T. commodus. Genotyping of sperm within sperm storage organs revealed high levels of multiple mating by females in both species, but females utilized sperm from just 75% and 60% of their mates, respectively. Paternity was skewed toward a subset of fathers; skew was strongest in T. oceanicus and declined with the number of fathers represented in both species. Thus, postcopulatory sexual selection is strong in natural populations of both species and must be taken into account when estimating total sexual selection acting on these species. More generally, we argue that more effort should be made to measure the strength of postcopulatory sexual selection in other species, and to integrate episodes of pre- and postcopulatory selection, if we are to gain an accurate appreciation of the evolutionary consequences of sexual selection.