Abstract
Sex reversal is a mismatch between genetic sex (sex chromosomes) and phenotypic sex (reproductive organs and secondary sexual traits). It can be induced in various ectothermic vertebrates by environmental perturbations, such as extreme temperatures or chemical pollution, experienced during embryonic or larval development. Theoretical studies and recent empirical evidence suggest that sex reversal may be widespread in nature and may impact individual fitness and population dynamics. So far, however, little is known about the performance of sex-reversed individuals in fitness-related traits compared to conspecifics whose phenotypic sex is concordant with their genetic sex. Using a novel molecular marker set for diagnosing genetic sex in agile frogs (Rana dalmatina), we investigated fitness-related traits in larvae and juveniles that underwent spontaneous female-to-male sex reversal in the laboratory. We found only a few differences in early life growth, development, and larval behavior between sex-reversed and sex-concordant individuals, and altogether these differences did not clearly support either higher or lower fitness prospects for sex-reversed individuals. Putting these results together with earlier findings suggesting that sex reversal triggered by heat stress may be associated with low fitness in agile frogs, we propose the hypothesis that the fitness consequences of sex reversal may depend on its etiology.
Highlights
Sex is a fundamental aspect of individual state in all sexually reproducing organisms
Survival rate until dissection did not depend on genetic sex (18 females and 16 males died; hazard ratio: 0.84, 95% confidence intervals (CI): 0.60–2.38)
We confirmed that female-to-male sex reversal occurs in agile frogs at a relatively low frequency (6.4%) in the absence of thermal stress, and demonstrated that it was independent of chemical treatments representing ecologically relevant concentrations of carbamazepine, terbuthylazine, and chlorpyrifos
Summary
Sex is a fundamental aspect of individual state in all sexually reproducing organisms. In species with genetic sex determination, where the process of gonad development is triggered by genomic elements, males and females often differ in their genetic make-up. The chromosome restricted to one sex (e.g., Y in male-heterogametic systems) is inclined to undergo degeneration, which may lead to sex differences in mortality rates. In species with environmental sex determination, where the fate of the gonads is decided by external factors such as temperature during early ontogeny, sex ratios and population viability may be vulnerable to environmental changes (Mitchell and Janzen, 2010). The way males and females come to be has crucial implications for population dynamics and thereby biodiversity conservation
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