Environmental heterogeneity shapes physiological traits in tropical direct‐developing frogs

Abstract

Tropical ectotherm species tend to have narrower physiological limits than species from temperate areas. As a consequence, tropical species are considered highly vulnerable to climate change since minor temperature increases can push them beyond their physiological thermal tolerance. Differences in physiological tolerances can also be seen at finer evolutionary scales, such as among populations of ectotherm species along elevation gradients, highlighting the physiological sensitivity of such organisms. Here, we analyze the influence of elevation and bioclimatic domains, defined by temperature and precipitation, on thermal sensitivities of a terrestrial direct‐developing frog ( Craugastor loki) in a tropical gradient. We address the following questions: (a) Does preferred temperature vary with elevation and among bioclimatic domains? (b) Do thermal tolerance limits, that is, critical thermal maximum and critical thermal minimum vary with elevation and bioclimatic domains? and (c) Are populations from high elevations more vulnerable to climate warming? We found that along an elevation gradient body temperature decreases as environmental temperature increases. The preferred temperature tends to moderately increase with elevation within the sampled bioclimatic domains. Our results indicate that the ideal thermal landscape for this species is located at midelevations, where the thermal accuracy ( d b ) and thermal quality of the environment ( d e ) are suitable. The critical thermal maximum is variable across elevations and among the bioclimatic domains, decreasing as elevation increases. Conversely, the critical thermal minimum is not as variable as the critical thermal maximum. Populations from the lowlands may be more vulnerable to future increases in temperature. We highlight that the critical thermal maximum is related to high temperatures exhibited across the elevation gradient and within each bioclimatic domain; therefore, it is a response to high environmental temperatures.

Isolation by environment is more important than isolation by distance along a tropical gradient in direct developing frogs

“…Temperature and precipitation are important factors influencing the natural history and ecology of these direct-developing frogs, characterized by the lack of a water-dwelling larval phase and their use of substrate humidity for reproduction (Duellman & Trueb, 1994). The Central Depression slope cluster presents a thermal landscape different from the Pacific slope, where the former is characterized mainly by temperature seasonality (Percino-Daniel et al, 2021). Hence, our results suggest that the abiotic variables considered in our study, temperature and precipitation, have an important role in the pattern of IBE.…”

“…The climatic variables used here temperature and precipitation are important in general for amphibians, given that determine their body temperature and hence all their activities. In a previous study, Percino et al (2021), studied some physiological traits from the same individuals of the species studied here. The frogs that inhabit at the Central Depression slope showed a different thermal sensitivity compared with the populations from Pacific slope.…”

“…We collected 90 tissue samples of the direct-developing frog C. loki from 13 different localities in the Sierra Madre de Chiapas of southern Mexico (Figure 1, Table S1). Our sampling regime was designed to capture environmental variation along an elevation gradient, with sampling sites ranging from 120 to 2200 masl (Percino-Daniel et al, 2021).…”