Testing the climate variability hypothesis in thermal tolerance limits of tropical and temperate tadpoles

Abstract

Aim The climate variability hypothesis (CVH) states that a positive relationship may exist between the breadth of thermal tolerance range and the level of climatic variability experienced by taxa with increasing latitude, especially in terrestrial ectotherms. Under CVH, we expected to find a correspondence between both thermal tolerance limits (CTmax and CTmin), ambient extreme temperature and the range sizes of species. We examined the validity of these predictions in a lowland tropical and a temperate tadpole assemblage.Location Lowland Neotropics (Bahia, Brazil) and Palaearctic (Iberian Peninsula and North Africa).Method We employed phylogenetic eigenvector regression (PVR) and Pagel's lambda to analyse phylogenetic signals in CTmax and CTmin. We used phylogenetic regression analyses (PGLS) to test the relationships between thermal limits, range size and temperature predictors (measured at the macroscale and microhabitat levels) and phy-ANOVA to compare both the physiological traits and thermal regimen in both tropical and temperate assemblages.Results We documented moderate-to-strong phylogenetic signal in both heat and cold tolerance. Temperate-zone tadpoles had broader thermal tolerances than tropical ones. Thermal tolerance range was correlated with range sizes and was explained by seasonal thermal range predictors at the global scale. Both macro-and microclimate temperature variables provided the best predictive multivariate models of thermal limits at the global scale. Microclimatic predictors, however, were the main determinants of CTmax and CTmin variation at the local level of tropical and temperate communities respectively.Main conclusions Thermal tolerance range increases with latitude in tadpoles due to the higher increase in cold tolerance in temperate tadpoles. At the global scale, both macro-and microenvironment thermal information were reliable predictors of critical thermal limits and thermal tolerance range, as CVH predicts. However, thermal limits were best predicted by temperatures of the micro-habitat at the regional level, thus suggesting that physiological thermal boundaries may be governed by thermal selection.

Are glacial refugia hotspots of speciation and cytonuclear discordances? Answers from the genomic phylogeography of Spanish common frogs

“…The accuracy of the projected distributions is obviously bounded by SDM performance in capturing the complex ecological conditions that define species' preferences (notably microhabitats), and bioclimatic reconstructions are only informative of the latest stages of the Pleistocene (i.e., not when the lineages initially diverged). Here, glacial instead of post‐glacial expansions coincide with the expectations for R. temporaria , an ecologically versatile species often associated to the Euro‐Siberian realm (sensu De Lattin, ; Schmitt & Varga, ), and one of the most cold‐tolerant amphibians of temperate Europe, both at the larval (Gutiérrez‐Pesquera et al, ) and terrestrial stages (critical thermal minimum as low as −2.4°C, A.G. Nicieza, unpublished data).…”

Elevational and microclimatic drivers of thermal tolerance in Andean Pristimantis frogs

“…Contrary to expectations, forest frogs, although exhibiting lower heat tolerances, are less prone to suffer heat impacts because forest canopy shields ground temperatures yielding cooler tmax. Similarly, lower risk to heat impacts was found in forest amphibian tadpole communities with lower pond tmax than open ponds (Duarte et al., ; Gutiérrez‐Pesquera et al., ) and in terrestrial ectotherms inhabiting areas with diverse vegetation coverage resulting in contrasting temperatures (Kaspari et al., ; Kearney, Shine, & Porter, ). Given Pristimantis’ direct development, we believe that these same results would apply across the whole life cycle as eggs are usually laid within the same shelters as those used by adults.…”

“…Our results appear to uncover two weaknesses of current macrophysiological trend analyses. First, the analyses of physiological variation through geographical gradients do not usually account for the thermal heterogeneity associated with microenvironments where organisms actually live (Potter et al., ; Sears, Raskin, & Angilletta, ) which, otherwise, may represent a main driver of thermal tolerance variance (Gutiérrez‐Pesquera et al., ; Kaspari et al., ). We found that habitat thermal diversity (forest versus open areas) appears to drive CTmax variation, and its link to tmax suggests local thermal adaptation to the significantly different peak temperatures experienced in both habitats (around 8°C higher in open as opposed to forest environments) (also see Muñoz et al., ).…”

“…An operative metric to estimate the eventual occurrence of acute heat stress is the warming tolerance (i.e. the difference between CTmax and the maximum exposure temperature) taken at both the micro (substrate temperature, tmax)‐ and the macro (air temperature, TMAX)‐climatic scales (Duarte et al., ; Gutiérrez‐Pesquera et al., ; Hoffmann, Chown, & Clusella‐Trullas, ). Similarly, we can define cooling tolerance as the risk to suffer cold shocks measured as the difference between the minimum exposure temperature, also taken at both micro (substrate, tmin)‐ and macro (air, TMIN)‐climatic scales, and CTmin (Gutiérrez‐Pesquera et al., ; Sunday et al., ).…”

Linear reaction norms of thermal limits in Drosophila: predictable plasticity in cold but not in heat tolerance

“…The lack of, or limited, support in this and other studies of insects for the latitudinal hypothesis, may be a consequence of the use of macroclimate data, as opposed to microclimate data which may give a much more exact picture of the environmental heterogeneity faced by organisms (Potter, Woods & Pincebourde ; Gutiérrez‐Pesquera et al . ).…”