A user's guide for understanding reptile and amphibian hydroregulation and climate change impacts

Abstract

Human impacts on ecosystems have intensified variation in water variability for terrestrial life, thus challenging the maintenance of water balance, or hydroregulation. The accelerated development and accessibility of technologies and computational models over the past decade have enabled researchers to predict changes in animal hydroregulation and environmental water with greater spatial and temporal precision. Focusing on reptiles and amphibians, we discuss current methods, limitations and advances for quantifying ecologically relevant metrics of environmental water stressors and organismal responses to both acute and long-term water stress that are applicable for conservation and management. We also highlight approaches that integrate environmental water data with an organism's water balance and physiological, behavioural and life history traits to predict the limits of species' responses and assess their vulnerability to climate change. Finally, we outline promising future directions and opportunities in hydroregulation studies with a conservation focus, including broader inferences about acclimation responses, linking gene expression to functional changes, and exploring inter- and transgenerational plasticity and adaptive evolution. Advances in these fields will facilitate more accurate assessments of species' capacities and the limits of hydroregulation in response to a more variable and unpredictable future climate.

Keywords: Dehydration; drought; ectotherm; exposure; sensitivity; vulnerability; water balance.

Figure 1

Overview of the landscape hydrology and animal hydroregulation. Blue text indicates environmental water that can influence hydroregulation such as precipitation and evapotranspiration, atmospheric and soil moisture content, water bodies (outlined in Table 1) and their interaction with external factors such as wind speed, temperature, thermal radiation and substrate composition. The landscape includes habitats with different water stressors represented by VPD (in kilopascals), which is calculated from measured air temperature (in degrees Celsius) and atmospheric moisture content (e.g. RH in %). Hydroregulation includes water gain/loss, water storage and their interaction with extrinsic and intrinsic factors. Representative landscape and animals are based on Borneo’s ecosystem. The representative terrestrial lizard is the earless monitor lizard (Lanthanotus borneensis), the representative arboreal frog is the Wallace’s flying frog (Rhacophorus nigropalmatus) and the representative subterranean caecilian is the Metang caecilian (Ichthyophis biangularis). Illustration by S. Buttimer.

Figure 2

Example variation in monthly precipitation in Sydney, Australia, from 1970–2024. Monthly precipitation data represented by thin grey lines from the Australian Government Bureau of Meteorology, with the 5-year rolling mean in thick black lines. The 10th and 90th month-specific percentiles represent dry and wet thresholds, respectively. Example durations (D) for extremely dry or wet months (green points with black outline) are shown, which is calculated as the number of consecutive months above the wet and below the dry thresholds. Example calculations of intensity (I), magnitude (M) and severity (S) are also shown for a 3-month wet event (D = 3) with a departure of i₁, i₂ and i₃ from the threshold. Frequency can be calculated as the number of times the monthly precipitation is above the wet and below the dry thresholds.

Figure 3

Example genes identified in response to water stress. Genes are grouped by the following functions: skin water preservation, osmoregulation, damage repair and immunity. Specific functions of the genes are described on the right side with the taxon in which the function has been demonstrated. Numbers inside the square bracket indicate the species and reference, Gopherus agassizii^{[1,4,6,10–15]} (Tollis et al., 2017), X. laevis^[2,3] (Caine and Mclaughlin, 2013; Malik et al., 2023), Liolaemus fuscus^[5,9] (Araya-Donoso et al., 2022), Xenopus tropicalis^[7] (Shibata et al., 2014) and X. laevis/Bufo viridis/Fejervarya cancrivora^[8] (Li et al., 2022).