Global analysis of thermal tolerance and latitude in ectotherms

Abstract

A tenet of macroecology is that physiological processes of organisms are linked to large-scale geographical patterns in environmental conditions. Species at higher latitudes experience greater seasonal temperature variation and are consequently predicted to withstand greater temperature extremes. We tested for relationships between breadths of thermal tolerance in ectothermic animals and the latitude of specimen location using all available data, while accounting for habitat, hemisphere, methodological differences and taxonomic affinity. We found that thermal tolerance breadths generally increase with latitude, and do so at a greater rate in the Northern Hemisphere. In terrestrial ectotherms, upper thermal limits vary little while lower thermal limits decrease with latitude. By contrast, marine species display a coherent poleward decrease in both upper and lower thermal limits. Our findings provide comprehensive global support for hypotheses generated from studies at smaller taxonomic subsets and geographical scales. Our results further indicate differences between terrestrial and marine ectotherms in how thermal physiology varies with latitude that may relate to the degree of temperature variability experienced on land and in the ocean.

Plasticity in thermal tolerance has limited potential to buffer ectotherms from global warming

“…As a result, behavioural thermoregulation is less effective at reducing variability in the minimum temperatures experienced and in preventing exposure to extreme cold. This mechanism may also contribute to parallel geographical patterns seen in inherent thermal tolerances, where CT min changes more quickly with latitude and elevation than CT max [37,50,51]. The higher thermal plasticity of organisms in aquatic versus terrestrial habitats was unexpected (figures 1 and 3; but see [38]).…”

“…For each hypothesis, an a priori set of linear mixed models was constructed that included terms and interactions that might explain variation in thermal tolerance plasticity (see below). All models included a nested, hierarchical random term representing taxonomic affinities of the taxa included (phylum/class/order/family/genus/spp) to account for nonindependence of data since no phylogenetic tree is available for all taxa included in this study [37,38]. Model validation was conducted by examining diagnostic plots (e.g.…”

Evolutionary stasis and lability in thermal physiology in a group of tropical lizards

“…Moreover, although cybotoid anoles show relatively little variation in heat sensitivity, some other anole clades have diversified extensively while adapting to different thermal environments [54]. Looking more broadly, other lizard species possess heat tolerances that approach 508C (reviewed in [58,59]), suggesting that if genetic constraints exist in lizards, they are phylogenetically localized. Finding an explanation for variation among clades in physiological diversity could aid in assessing ectotherms' vulnerability to climate warming, but it is a challenge that will require integration of physiological, behavioural, and evolutionary approaches.…”

Prediction of phylogeographic endemism in an environmentally complex biome

“…These issues are particularly relevant in tropical regions, where deep phylogeographic structuring and concomitant high genetic endemism are prevalent [5,6]. Hypotheses to explain high diversity and endemism in the tropics frequently invoke climatic heterogeneity in space [7] and time [8], often associated with the expectation that tropical species have restricted physiological tolerances [9,10].…”