Snow skinks (Niveoscincus ocellatus) do not shift their sex allocation patterns in response to mating history

Abstract

Theory predicts that where there is variation in the number of males and females available for mating (the breeding/operational sex ratio) frequency-dependent selection should favour overproduction of the less abundant sex. We used mating history as a proxy for male availability to examine female sex allocation responses to variation in the operational sex ratio in a large free-ranging population of Niveoscincus ocellatus, a viviparous skink. While we found evidence for shifts in offspring sex allocation and the local operational sex ratio, both between and within years, we failed to find patterns corresponding to those predicted by theory. These results are in accordance with a growing body of literature on facultative sex allocation, which suggests that, despite plausible benefits, there is often little evidence for adaptive sex allocation shifts in wild vertebrate populations. In this study, we examine the inconsistencies between theoretical predictions and empirical patterns, specifically relating to variation in the operational sex ratio, and the accuracy with which empirical studies adhere to the assumptions of theoretical models. We suggest that alternative hypotheses, which focus on individual level decisions in relation to population parameters influenced by the operational sex ratio, may more closely predict the sex allocation patterns observed.