Operational sex ratio bias due to sex-specific cohort splitting in response to predation

The operational sex ratio (OSR), i.e., the local ratio of fertilizable females to sexually active males at any given time, is of key importance for the strength of sexual selection and the reproduction of populations. We hypothesize that sex-specific cohort splitting, i.e., when one sex mostly metamorphoses while the other mostly enters diapause, may lead to OSR bias in nature. The OSR of an aquatic moth, Acentria ephemerella, has been shown to be strongly male-biased in situ. Here, we use a mesocosm experiment in which we determine the sexes of active, diapausing, and metamorphosing larvae to test whether the male bias in Acentria is due to sex-specific mortality or sex-specific cohort-splitting. Fish predation dd not result in a strong male bias of the whole population but increased male bias in pupae and female bias in diapausing larvae. The opposite effect of fish on pupal versus diapausing larval sex ratios suggests that fish-induced sex-specific cohort splitting, rather than sex-s..., The aquatic moth Acentria ephemerella (Crambidae) displays a pronounced sexual wing and size dimorphism (Berg, 1942). Female pupae and adult life stages are larger than male pupae and adult life stages (Berg, 1942; Miler et al., 2014). The adult females are predominantly rudimentarily winged (brachyptery > 99%), aquatic throughout their life and display morphological adaptations to the aquatic habitat such as swimming legs (Berg, 1942). Adult males in contrast are winged and emerge from the water column after metamorphosis (Berg, 1942). Acentria is a capital breeder with a short adult life span of 1–3 days and the number of eggs can be counted in advanced pupal stages (Berg, 1942; Miler et al., 2014). Mating occurs at the water surface, with the abdominal apex of the aquatic adult females reaching above the water surface (Berg, 1942). During mating, the terrestrial males transfer a spermatophore into the bursa copulatrix of the females which is located ventrally between the..., , # Operational sex ratio bias due to sex-specific cohort splitting in response to predation

[https://doi.org/10.5061/dryad.8kprr4xtg](https://doi.org/10.5061/dryad.8kprr4xtg)

## Summary of dataset contents, contextualized in experimental procedures and results

Operational sex ratio (OSR) is of key importance for the strength of sexual selection and the reproduction of populations. We suggest that n important mechanism causing OSR bias is sex-specific cohort splitting, i.e., when one sex mostly metamorphoses, whereas the other one mostly enters diapause. The OSR of an aquatic moth Acentria ephemerella, has been shown to be strongly male biased in situ. Here, we use a mesocosm experiment in which we determine the sexes of active, diapausing, and metamorphosing moths to test whether male bias in this key herbivore is due to sex-specific mortality or due to sex-specific cohort-splitting. Fish predation did not result in male bias of the whole population, but strongly enhanced male bias fo...,