Comparing Factors that Shape the Relationship Between Pre- and Post-Copulatory Reproductive Investments

Abstract

Sexual selection is an evolutionary process that drives the emergence of complex sexual traits. Shifts in the preferences of one sex can impose selection on traits in the other, resulting in the codivergence of these traits among taxa. Sexual traits can be broken down into two components: pre-copulatory traits – physical and behavioural characteristics involved in attracting and competing for mates – and post-copulatory traits, which operate after mating. In this review, pre-copulatory traits are categorised into ornaments, weapons, and body size, and sperm competition is the key post-copulatory mechanism focused on. I integrate theoretical and empirical literature to examine how investment in male pre- and post-copulatory traits covaries across species, whether these relationships differ among types of pre-copulatory traits, and how patterns of energetic investment vary within and among taxa in relation to mating systems. Overall, past studies indicate that both positive and negative correlations between pre- and post-copulatory traits occur across taxa. Body size shows a trade-off with post-copulatory traits among species but a positive relationship within species, a pattern not observed for ornaments or weapons. Mating systems generally shaped these relationships as predicted, with strong female monopolisation favouring negative correlations and weak monopolisation favouring positive ones; however, ecological context may override mating system effects, highlighting environmental conditions as key determinants of pre- and post-copulatory trait covariation.