Studies of mating preferences have largely neglected the potential effects of individuals encountering their previous mates (‘directly sexually familiar’), or new mates that share similarities to previous mates, e.g. from the same family and/or environment (‘phenotypically sexually familiar’). Here, we show that male and female Drosophila melanogaster respond to the direct and phenotypic sexual familiarity of potential mates in fundamentally different ways. We exposed a single focal male or female to two potential partners. In the first experiment, one potential partner was novel (not previously encountered) and one was directly familiar (their previous mate); in the second experiment, one potential partner was novel (unrelated, and from a different environment from the previous mate) and one was phenotypically familiar (from the same family and rearing environment as the previous mate). We found that males preferentially courted novel females over directly or phenotypically familiar females. By contrast, females displayed a weak preference for directly and phenotypically familiar males over novel males. Sex-specific responses to the familiarity of potential mates were significantly weaker or absent in Orco1 mutants, which lack a co-receptor essential for olfaction, indicating a role for olfactory cues in mate choice over novelty. Collectively, our results show that direct and phenotypic sexual familiarity is detected through olfactory cues and play an important role in sex-specific sexual behaviour.

It is now clear in many species that male and female genital evolution has been shaped by sexual selection. However, it has historically been difficult to confirm correlations between morphology and fitness, as genital traits are complex and manipulation tends to impair function significantly. In this study, we investigate the functional morphology of the elongate male intromittent organ (or processus) of the seed bug Lygaeus simulans, in two ways. We first use micro-computed tomography (micro-CT) and flash-freezing to reconstruct in high resolution the interaction between the male intromittent organ and the female internal reproductive anatomy during mating. We successfully trace the path of the male processus inside the female reproductive tract. We then confirm that male processus length influences sperm transfer by experimental ablation and show that males with shortened processi have significantly reduced post-copulatory reproductive success. Importantly, male insemination function is not affected by this manipulation per se. We thus present rare, direct experimental evidence that an internal genital trait functions to increase reproductive success and show that, with appropriate staining, micro-CT is an excellent tool for investigating the functional morphology of insect genitalia during copulation.

Greenway et al. introduce the concept of mating failure, the failure to produce offspring.

Mating failure, characterized by the lack of production of offspring following copulation, is relatively common across taxa yet is little understood. It is unclear whether mating failures are stochastic occurrences between incompatible mating partners or represent a persistent, meaningful phenotype on the part of one or other sex. Here we test this in the seed bug Lygaeus simulans, by sequentially mating families of males with randomly allocated unrelated females and calculating the repeatability of mating outcome for each individual male and family. Mating outcome is significantly repeatable within individual males but not across full‐sib brothers. We conclude that mating failure represents a consistent male‐associated phenotype with low heritability in this species, affected by as yet undetermined environmental influences on males.

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.