Sex-reversed males are morphologically similar but have lower testosterone levels compared to sex-concordant males in the agile frog

Nadine Lehofer, Veronika Bókony, Andrea Kásler, Zsanett Mikó, Nikolett Ujhegyi, Emese Balogh, Virginie Canoine, Edina Nemesházi 

Environment-induced sex reversal – the mismatch between genetic and phenotypic sex caused by external conditions during early development – is increasingly documented in ectothermic vertebrates, yet its fitness-related consequences in natural populations remain poorly tested. In the agile frog (Rana dalmatina), an emerging model species of environmental sex reversal, sex-reversed (XX) males have lower mating success in the wild compared to sex-concordant (XY) males, but the mechanisms are unclear. To address this gap, we compared sex-reversed and sex-concordant males upon arrival to a breeding pond. We assessed morphometric traits that are relevant to male breeding success in anurans (snout-vent length, body mass, scaled mass index as a measure of body condition, forearm length and width, and nuptial pad size and coloration). Furthermore, we measured waterborne concentrations of testosterone and corticosterone. Sex-reversed males were indistinguishable from sex-concordant males across all measured traits, except that the former had significantly lower testosterone concentrations. Typical male morphological appearance combined with endocrine differences might contribute to the reduced paternity success previously reported in XX males. Such mismatches between various aspects of phenotype as well as with genotype deserve more attention in species susceptible to sex reversal, especially under the ongoing environmental change.