Testing for cryptic male mate choice in an insect with high mating failure

Post-copulatory sexual selection is an important component of sexual selection. Whilst traditionally studied in terms of sperm competition and cryptic female choice, males may also exert post-copulatory mate choice, for instance in terms of whether to inseminate a female during copulation or how many sperm to pass. Disentangling these processes of post-copulatory sexual selection is challenging, not least as male and female processes are unlikely to be fully independent. Here we take an experimental approach to explore cryptic male choice in the seed bug Lygaeus simulans, a species where 40–60% of copulations do not involve sperm transfer. Evidence suggests that this is a male-driven process, with males more likely to pass sperm to large females. However, large females may require or accept sperm more than smaller females. Across two experiments, we attempted to change the value ascribed by a male to a female of a given size, and so change patterns of sperm transfer, definitively showing a male effect. We varied (1) access to male competitors, and (2) access to females, prior to mate trials, to manipulate male experience. However, whilst recovering evidence that male pre-copulatory behaviour changed in our second experiment, and confirming previous results that larger females are more likely to receive sperm and produce offspring, we found little effect of our experimental manipulations. As such, our data remain consistent with the hypothesis of cryptic male choice for large females, but evidence definitively associating insemination success with males remains out of reach.