Latitude-Induced and Behaviorally Thermoregulated Variations in Upper Thermal Tolerance of Two Anuran Species

Abstract

Although thermal tolerance along geographical gradients gives an insight into species’ response to climate change, current studies on thermal tolerance are strongly skewed towards global-scale patterns. As a result, intraspecific variations are often assumed to be constant, despite a lack of evidence. To understand population-specific responses to thermal stress, we investigated the presence of intraspecific variations in the critical thermal maximum (CTmax) of tadpoles in two anuran species, Rana uenoi and Bufo sachalinensis. The study was conducted across a five-degree latitudinal gradient in the Republic of Korea. We exposed the tadpoles to increasing temperatures and recorded the CTmax for 270 R. uenoi individuals from 11 sites, collected in rice paddies, and for 240 B. sachalinensis individuals from ten sites, collected in reservoirs. We also recorded the swimming performance and behavior of the tadpoles when placed in an experimental apparatus during CTmax measurements. We then used linear regressions to determine the relationship between abiotic factors and CTmax. In R. uenoi, we found a positive relationship between latitude and CTmax, but the tadpoles did not display specific thermoregulatory behaviors. In B. sachalinensis, none of the abiotic factors such as climate and geographic coordinates were related to CTmax, but we detected a tendency to swim close to the water surface when water temperature was increasing. For R. uenoi, we tentatively relate the CTmax variability across the latitudinal gradient to a physiological adaptive response associated with habitat characteristics that are assumed to be fluctuating, as the species inhabits small water bodies prone to drying out. In the case of B. sachalinensis, the behavior observed may be linked to oxygen depletion and thermoregulation, as it may buffer temperature changes in the absence of physiological adjustment. These findings suggest that intra-specific variations in CTmax are greater than generally accounted for, and thermal conditions of natural environments are important for understanding thermal tolerance in ectothermic species. Our results highlight that species’ specific responses to climate warmings need to be studied to better protect species against climate change.

Genetically based variation in heat tolerance covaries with climate in a globally important disease vector

“…The ability, or not, to behaviorally thermoregulate has been shown to impact local adaptation (Huey et al, 2003). In a study on two frog species, one species that does not behaviorally thermoregulate had a latitudinal cline in CTmax, but this pattern was not detected in a second species that does behaviorally thermoregulate allowing it to buffer changes in temperature without adapting to local climates (Kim et al, 2022). Some known mechanisms for Aedes mosquitoes to behaviorally thermoregulate are altering wing beat frequency and only increasing activity during cooler parts of the day (Reinhold et al, 2018).…”

Respostas fisiológicas e comportamentais de pequenos animais ectotérmicos a variações térmicas no espaço e no tempo

“…Deutsch et al, 2008;Sentinella et al, 2020;. Global studies, however, have usually used only one population per species (Kim et al, 2022), neglecting that intraspecific variation exists at both sides of the WT equation Villeneuve et al, 2021). Also, recent studies have shown that species at the same latitude or elevation may have contrasting between WT and population dynamics, range limits, or extinction risk (Soroye et al, 2020).…”