Thermal Acclimation to the Highest Natural Ambient Temperature Compromises Physiological Performance in Tadpoles of a Stream-Breeding Savanna Tree Frog

Abstract

Amphibians may be more vulnerable to climate-driven habitat modification because of their complex life cycle dependence on land and water. Considering the current rate of global warming, it is critical to identify the vulnerability of a species by assessing its potential to acclimate to warming temperatures. In many species, thermal acclimation provides a reversible physiological adjustment in response to temperature changes, conferring resilience in a changing climate. Here, we investigate the effects of temperature acclimation on the physiological performance of tadpoles of a stream-breeding savanna tree frog (Bokermannohyla ibitiguara) in relation to the thermal conditions naturally experienced in their microhabitat (range: 18.8–24.6°C). We quantified performance measures such as routine and maximum metabolic rate at different test (15, 20, 25, 30, and 34°C) and acclimation temperatures (18 and 25°C). We also measured heart rate before and after autonomic blockade with atropine and sotalol at the respective acclimation temperatures. Further, we determined the critical thermal maximum and warming tolerance (critical thermal maximum minus maximum microhabitat temperature), which were not affected by acclimation. Mass-specific routine and mass-specific maximum metabolic rate, as well as heart rate, increased with increasing test temperatures; however, acclimation elevated mass-specific routine metabolic rate while not affecting mass-specific maximum metabolic rate. Heart rate before and after the pharmacological blockade was also unaffected by acclimation. Aerobic scope in animals acclimated to 25°C was substantially reduced, suggesting that physiological performance at the highest temperatures experienced in their natural habitat is compromised. In conclusion, the data suggest that the tadpoles of B. ibitiguara, living in a thermally stable environment, have a limited capacity to physiologically adjust to the highest temperatures found in their micro-habitat, making the species more vulnerable to future climate change.

Thermal tolerance and acclimation capacity in the European common frog (Rana temporaria) change throughout ontogeny

“…This geographic pattern can be explained by the climate variability hypothesis (Bozinovic et al, 2011; Ghalambor et al, 2006; Janzen, 1967; Stillman, 2003) since latitudinal gradients vary in mean temperature and seasonal changes in temperature. Besides these geographic patterns of thermal adaptation, thermal tolerance is also influenced by several extrinsic and intrinsic factors such as body mass (Ospina & Mora, 2004; Peralta‐Maraver & Rezende, 2021; Ribeiro et al, 2012), thermal history (Nyamukondiwa & Terblanche, 2010; but not: Longhini et al, 2021), physiological condition (Rezende et al, 2014), phylogeny (Hoffmann et al, 2013; but not: Simon et al, 2015), and ontogeny (Cupp, 1980; Dahlke et al, 2020; Enriquez‐Urzelai, Sacco, et al, 2019; Floyd, 1983; Turriago et al, 2015).…”

Fungal pathogen infection intensity associated with reproductive mode and elevation in an afrotropical anuran community

“…One framework for explaining why amphibians at higher elevations have higher pathogen loads is the thermal mismatch hypothesis, in which hosts are predicted to be more susceptible to parasites when environmental conditions move away from the host's ideal thermal range (Cohen et al, 2017). In particular, amphibian exposure to warmer temperatures and temperature variability is known to reduce physiological fitness (Rome et al, 1992;Longhini et al, 2021), and increase disease susceptibility and mortality (Raffel et al, 2006;Rohr & Raffel, 2010;Neely et al, 2020). Tropical amphibians, which live at consistently higher temperatures than temperate amphibians, are generally more sensitive to temperature changes associated with global warming (Deutsch et al, 2008;Duarte et al, 2012) and have a narrower thermal range (Rohr et al, 2018).…”

Physiological Performance Curves: When Are They Useful?

“…Often, logistics, life-histories, and the delopmental stages of a focal animal can make experimental designs that acclimate the same individual to multiple environmental conditions challenging if not impossible. In this special issue, for instance, Longhini et al (2021) analyzed thermal performance curves for aerobic scope in tadpoles of the stream-breeding savanna tree frog ( Bokermannohyla ibitiguara ) to determine their capacity for reversible acclimation. Here, a within-individual approach would likely not be possible because temporal responses to the changing thermal environment would be confounded with developmental stage.…”