Thermal biology of the toadRhinella schneideriin a seminatural environment in southeastern Brazil

Abstract

The toad, Rhinella schneideri, is a large-bodied anuran amphibian with a broad distribution over South America. R. schneideri is known to be active at night during the warm/rainy months and goes into estivation during the dry/cold months; however, there is no data on the range of body temperatures (Tb) experienced by this toad in the field, and how environmental factors, thermoregulatory behaviors or activity influence them. By using implantable temperature dataloggers, we provide an examination of Tb variation during an entire year under a seminatural setting (emulating its natural habitat) monitored with thermosensors. We also used data on preferred Tb, allowing us to express the effectiveness of thermoregulation quantitatively. Paralleling its cycle of activity, R. schneideri exhibited differences in its daily and seasonal profile of Tb variation. During the active season, toads spent daytime hours in shelters and, therefore, did not explore microhabitats with higher thermal quality, such as open areas in the sun. At nighttime, the thermal suitability of microhabitats shifted as exposed microhabitats experienced greater temperature drops than the more insulated shelter. As toads became active at night, they were driven to the more exposed areas and, as a result, thermoregulatory effectiveness decreased. Our results, therefore, indicate that, during the active season, a compromise between thermoregulation and nocturnal activity may be at play. During the estivation period, R. schneideri spent the entire day cycle inside the shelter. As toads did not engage in nocturnal activity in those areas with low thermal quality, the overall effectiveness of thermoregulation was, indeed, elevated. In conclusion, we showed that daily and seasonal variation in Tb of an anuran species is highly associated with their respective pattern of activity and may involve important physiological and ecological compromises.

A macroecological approach to evolutionary rescue and adaptation to climate change

“…Third, σ can be obtained by using experimental data, which is ca 2.5°C (see Fig. 5 from Anderson and Andrade 2017; see also Noronha-de-Souza et al 2015). Thus, we can assume values of SD ranging between 2.0°C and 2.5°C for the species to calculate the Haldanes.…”

Ecophysiology of Amphibians: Information for Best Mechanistic Models

“…Early physiological ecology studies with adult anurans resulted mainly in physiology approaching ecology (more than ecology approaching physiology, as in the lizard studies described above). Although recent studies [39][40][41] take for granted the principle that thermal and hydric relationships are physiologically inseparable, this principle was developed over time through models and studies dating back to the 1970s. Several important papers preceded the seminal Tracy's monograph [42], and those papers dealt with crucial topics such as the relationship between thermal (energy) and water (mass) balances, and the implications of such balance for amphibian thermoregulation.…”

“…The discovery of great diversity in the cutaneous resistance of anuran species (mostly but not exclusively tree frogs) was remarkable and brought about a new dimension of complexity into the dynamics between water and temperature/energy balance [26,43]. Consequently, from the 2000s onwards water and thermal physiology re-emerged as integrated concepts (e.g., [39][40][41][44][45][46][47]). In this context, cutaneous resistance could be incorporated into a mechanistic model [14], even if highlighting the need of more data, given that evaporative water loss is but one parameter in the complex water balance of amphibians in nature.…”

Temperature and dehydration effects on metabolism, water uptake, and the partitioning between respiratory and cutaneous evaporative water loss in a terrestrial toad

“…Accordingly, terrestrial anurans are prone to experiencing variable degrees of hydration while active (see Tracy et al, 2014). As ectothermic organisms, amphibians may also experience wide fluctuations in body temperature, which generally mirrors the variation of their thermal environment (Seebacher and Alford, 2002;Noronha-de-Souza et al, 2015). Moreover, from the pioneering insights of the classic study of Tracy (1976), we now appreciate that thermoregulation and water balance are highly intertwined in terrestrial anurans (Feder and Burggren, 1992;Navas et al, 2008;Andrade et al, 2016).…”