Zoology/Biology session

Human activities induce numerous changes in the environment, and understanding the biological consequences of these changes is one of the key goals of ecology and conservation. A well-known form of human-induced change is the increase in the temperature of habitats (air, water, land), for example, due to the urban heat island effect and the lack of shading vegetation. These microclimatic changes particularly affect amphibians, which are already highly threatened in terms of conservation, partly because extreme temperatures experienced during the early stages of their development can lead to sex reversal. In sex-reversed individuals, the phenotypic sex differs from their genotypic sex, which can impact their fitness and thus population dynamics. Since anthropogenic environments may more frequently cause sex reversal, they can exert selective pressure on the propensity for sex reversal, potentially altering it through microevolution or phenotypic plasticity. In our study, we tested whether the propensity for sex reversal differs between agile frog (Rana dalmatina) populations from anthropogenic and forest habitats as a result of microevolutionary adaptation. This species has XX/XY sex chromosome system, and heat stress during the larval stage results in XX females developing into males. Such individuals are found at relatively high rates in wild populations, especially in urban and agricultural areas. In our experiment, we raised individuals from three forest and three anthropogenic habitats under identical conditions, from the eggs until two months after metamorphosis. Half of the animals were exposed to six days of heat stress during the third week of larval development, after which we compared the sex-reversal rates. As expected, the sex-reversal rate was higher in the heat-treated (26.67%) than in the control group (8.33%). However, the effect of heat treatment was similar in both habitat types (the interaction between treatment and habitat type had no significant effect). In the anthropogenic populations, sex reversal was approximately 2.33 times more frequent in both the heat-treated and control groups compared to the corresponding groups in forest populations, although this difference was only marginally significant. We also observed significant variability in sex-reversal rates among sibling groups. Our results suggest that the propensity for sex reversal in agile frogs is heritable and higher in anthropogenic populations, which results in more frequent sex reversal due to the higher incidence of heatwaves in their habitats compared to natural habitats. The fact that individuals from anthropogenic areas produced higher sex-reversal rates under both control and heat-treated conditions than those from forests suggests microevolutionary divergence between the two habitat types. However, further research is needed to determine whether this increased propensity for sex reversal is adaptive.