?Heat waves? experienced during larval life have species-specific consequences on life-history traits and sexual development in anuran amphibians

Extreme temperatures during heat waves can induce mass-mortality events, but can also exert sublethal negative effects by compromising life-history traits and derailing sexual development. Ectothermic animals may, however, also benefit from increased temperatures via enhanced physiological performance and the suppression of cold-adapted pathogens. Therefore, it is crucial to address how the intensity and timing of naturally occurring or human-induced heat waves affect life-history traits and sexual development in amphibians, to predict future effects of climate change and to minimize risks arising from the application of elevated temperature in disease mitigation. We raised agile frog (Rana dalmatina) and common toad (Bufo bufo) tadpoles at 19 degrees C and exposed them to a simulated heat wave of 28 or 30 degrees C for six days during one of three ontogenetic periods (early, mid or late larval development). In agile frogs, exposure to 30 degrees C during early larval development increased mortality. Regardless of timing, all heat-treatments delayed metamorphosis, and exposure to 30 degrees C decreased body mass at metamorphosis. Furthermore, exposure to 30 degrees C during any period and to 28 degrees C late in development caused female-to-male sex reversal, skewing sex ratios strongly towards males. In common toads, high temperature only slightly decreased survival and did not influence phenotypic sex ratio, while it reduced metamorph mass and length of larval development. Juvenile body mass measured 2 months after metamorphosis was not adversely affected by temperature treatments in either species. Our results indicate that heat waves may have devastating effects on amphibian populations, and the severity of these negative consequences, and sensitivity can vary greatly between species and with the timing and intensity of heat. Finally, thermal treatments against cold-adapted pathogens have to be executed with caution, taking into account the thermo-sensitivity of the species and the life stage of animals to be treated.

Automated summary

Heat waves can have devastating effects on amphibians, including increased mortality, delayed metamorphosis, decreased body mass, and sex reversal. The severity of these consequences can vary depending on the species and the timing and intensity of heat exposure. However, thermal treatments have no adverse effects on the body mass of juvenile amphibians.