Interplay of genotypic and thermal sex determination shapes climatic distribution in herpetofauna

Sex is a fundamental trait of all sexually reproducing organisms, and sex-determination systems show a great diversity across the tree of life. A growing body of evidence shows that genotypic and temperature-dependent sex determination (GSD and TSD, respectively) can coexist, which theoretically can have wide-ranging consequences for demography and population persistence, especially under climate change. Temperature-induced sex reversal, resulting from combined effects of sex chromosomes and environmental temperatures on sexual development, can explain the frequent transitions between GSD and TSD, and even between different GSD systems, that happened multiple times in ectothermic vertebrates. However, general lack of empirical data on the prevalence of sex reversal has long constrained the assessment of its evolutionary-ecological significance. Here we analysed an exhaustive compilation of available data to demonstrate that the climatic distribution of extant species is explained by the combination of their sex-chromosome system (GSD) and temperature reaction norm (TSD) across the phylogeny of amphibians and some reptiles. This pattern is in accordance with predictions of the ‘asymmetrical sex reversal’ theory, underscoring the importance of temperature-induced sex reversal in phylogeography, evolution, and species conservation under the threat of climate change, and highlighting the need for more empirical research on sex reversal in nature.