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"The phenomenon of sex reversal, where environmental conditions cause genotypically male (or female) individuals to develop as functional members of the opposite sex, has long attracted attention but key questions remain on the effects these transitions have at many ecological levels (e.g. population, community, ecosystem) and the reproductive viability of sex-reversed individuals. Bókony et al. (2026) investigated these somewhat neglected question in the Agile Frog (Rana dalmatina), a European native known for its high proportion of genetic females that reproduce as males. The authors performed both population surveys and a series of experiments to investigate the reproductive performance of sex-reversed individuals and the viability of their offspring in the face of environmental stressors. The experiments focused on comparing reproductive success between size and timing matched sex-reversed and sex-concordant males in the context of female choice and male-male competition. They also tracked the viability of embryos and post-metamorphic juveniles under normal conditions and under experimental manipulation of both temperature and exposure to a pathogen (ranavirus). The results were used to parameterize models designed to predict the population dynamic effects of sex-reversal in this species under various scenarios of future climate change (high temperatures during development are a key determinant of female-to-male sex reversal.) In male-male competition, sex-reversed males were not inferior to sex-concordant males, indicating that sex-reversal does not imply reduced reproductive success via intrasexual selection. Some evidence suggests females did not oviposit their entire clutch of eggs when paired with sex-reversed males, indicating intersexual selection may favor sex-concordant males. This could explain survey data in which sex-reversed males made a lower contribution to extant egg masses than expected based on their population frequency. In the context of population dynamics, the models predicted this bias in female choice and with climate change could significantly accelerate population decline. With regard to embryonic and juvenile survival, they detected no significant differences between the offspring of sex-reversed and sex-concordant males, but the offspring of sex-reversed males that underwent heat stress followed by ranavirus infection did show higher viral loads (but no difference in survival). Finally, the authors found that the offspring of sex-reversed males (which are all XX) are more likely to undergo sex-reversal themselves, which could dilute the impact of sex-reversal to mitigate sex ratio biases towards males in these populations."

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