Exploring the effects of extreme polyandry on estimates of sexual selection and reproductive success

Abstract

Multiple mating by females can dramatically alter selection on males by creating indirect interactions between rivals via sperm competition. Exactly how this behavior alters the relationship between male mating and fertilization success depends on multiple factors: re-mating frequency, sperm usage patterns, and mating assortment (the extent to which the most promiscuous individuals mate with each other). Here, we explore the role these elements play in determining sexual selection in a highly polygyandrous species, the squash bug Anasa tristis. Using replicated semi-natural enclosures, in which individuals were able to freely interact for a 2-week period, we tracked matings between individuals and subsequent female offspring production. Multiple mating was extremely common, resulting in very high levels of sperm competition intensity. However, network analysis revealed that the most promiscuous males mated with less polyandrous females, and therefore experienced lower levels of sperm competition. As a result, estimated male reproductive success increased with mating success, but this relationship varied according to the mode of sperm utilization with which it was calculated. Furthermore, females with more mating partners produced more offspring, suggesting they also benefit from mating multiply. Our findings highlight that polyandry has numerous and complex effects on sexual selection which may only be exposed when examined under naturalistic conditions.