Is mating failure caused by cryptic male choice in the seed bug Lygaeus simulans?

One yet unresolved question in the study of mating system evolution is the occurrence of mating failure, when individuals go through their lives without successfully mating. This includes the failure to produce offspring even following copulation, for instance due to insemination or fertilisation failure. Copulations are costly in a variety of ways, but also a fundamental route to fitness in sexual species, and so we should expect that engaging in copulations that generate no offspring should be strongly selected against. Nonetheless, it has become apparent that mating failure is quite common in nature. Here we consider post‐copulatory sexual selection in Lygaeus simulans seed bugs to test the hypothesis that the high levels of mating failure found in this species (approximately 40%–60%) are caused by cryptic male choice (i.e. males choosing not to inseminate a female during copulation). In our first experiment, we found that mating failure depended on female size, but not male size, with smaller females experiencing mating failure more frequently. Mechanistically this is likely to be due to copulation duration, as shorter copulations were more likely to lead to mating failure. Likewise, copulations with smaller females were shorter. In our second and third experiments, rates of mating failure decreased when pairs were allowed to repeatedly interact with the same partner over longer durations (hours through to days), implying that mating failure is not primarily caused by infertility or chronic mechanical failure. Instead, our results strongly suggest cryptic male choice as the cause of mating failure in this species. We expect cryptic mating failure–the failure to produce offspring due to fertilisation or insemination failure–to be strongly selected against because copulations are costly and are also a fundamental route to fitness. Mating failure is common in nature however, and in the seed bug Lygaeus simulans, rates are high (40%–60%). We performed experiments to investigate the causes of mating failure in L. simulans and found that mating failure is not primarily caused by infertility or chronic mechanical failure, but instead evidence strongly suggests that cryptic male choice is a key driver of mating failure in this species.