Operational sex ratio does not influence the evolution of male mate choice in the Indian meal moth

The strength of mate choice, pre-copulatory sexual selection more generally, is predicted to vary according to a range of social and demographic factors, including the operational sex ratio (OSR). The OSR influences the number of mating opportunities available to each sex, and can, therefore, strongly influence the degree of intrasexual competition and the cost of mate choice. Accordingly, many animals show short-term plasticity in the strength of mate choice in relation to changes in the OSR. However, whether such change persists over evolutionary time has rarely been tested experimentally. In this study, we examined how female mating success in relation to larval food level and body size differs according to the evolutionary history of their mates, in the Indian meal moth Plodia interpunctella. We used males from populations that have been reared at different adult sex ratios (and, therefore, OSRs) for 130 + generations. We found that small females were more likely to mate compared to large females; however, this effect could not be attributed exclusively to male mate choice. Larval food level also did not influence female mating success. Further, males from different sex ratio regimes did not differ in their likelihood of mating with small females, or those from high-food populations. We suggest that male post-copulatory choice is potentially more important than pre-copulatory choice in this species