Abstract
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.
Highlights
Mate choice involves the acceptance of some partners as mates and the rejection of others, and is virtually ubiquitous across the animal kingdom (Andersson 1994; Bonduriansky 2001; Rosenthal 2017)
Posttrial wing measurements revealed that there was no difference in size between high-food and low-food females (t test, t = -1.047, N = 243 high food, 243 low food, P = 0.29). This means that female body size is not confounded by larval food level, and so may separately influence female mating success
Is there pre-copulatory sexual selection in relation to female body size or condition in this species? Second, has the strength of male mate choice for these traits evolved in response to contrasting adult sex ratios over 140 + generations? Female larval food level did not influence female mating success, irrespective of the evolutionary history of her mating partner
Summary
Mate choice involves the acceptance of some partners as mates and the rejection of others, and is virtually ubiquitous across the animal kingdom (Andersson 1994; Bonduriansky 2001; Rosenthal 2017). The potential costs and benefits of mate choice are not constant, but can vary depending on the social or ecological environment (Jennions and Petrie 1997). This means that the optimal strength of choice for a given trait (or “choosiness” following the terminology of Reinhold and Schielzeth 2015) may depend strongly on the environment. The number of available mating opportunities is an important factor for determining the economics of choice, as it influences the risk of remaining unmated if suitable partners are not encountered (Jennions and Petrie 1997; Barry and Kokko 2010).
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