Disparate patterns of thermal adaptation between life stages in temperate vs. tropical Drosophila melanogaster

Many terrestrial ectothermic species exhibit limited variation in upper thermal tolerance across latitude. However, these trends may not signify limited adaptive capacity to increase thermal tolerance in the face of climate change. Instead, thermal tolerance may be similar among populations because behavioural thermoregulation by mobile organisms or life stages may buffer natural selection for thermal tolerance. We compared thermal tolerance of adults and embryos among natural populations of Drosophila melanogaster from a broad range of thermal habitats around the globe to assess natural variation of thermal tolerance in mobile vs. immobile life stages. We found no variation among populations in adult thermal tolerance, but embryonic thermal tolerance was higher in tropical strains than in temperate strains. We further report that embryos live closer to their upper thermal limits than adults – that is, thermal safety margins are smaller for embryos than adults. F1 hybrid embryos from crosses between temperate and tropical populations had thermal tolerance that matched that of tropical embryos, suggesting the dominance of heat‐tolerant alleles. Together, our findings suggest that thermal selection has led to divergence in embryonic thermal tolerance but that selection for divergent thermal tolerance may be limited in adults. Further, our results suggest that thermal traits should be measured across life stages to better predict adaptive limits.     

The role of hydro‐environmental factors in Mayfly (Ephemeroptera,Insecta) community structure: Identifying threshold responses

Freshwater organisms are threatened by changes in stream flow and water temperature regimes due to global climate change and anthropogenic activities. Threats include the disappearance of narrow‐tolerance species and loss of favorable thermal conditions for cold‐adapted organisms. Mayflies are an abundant and diverse indicator of river health that performs important functional roles. The relative importance of key hydro‐environmental factors such as water temperature and flow volumes in structuring these communities has rarely been explored in the tropical regions of Africa. Here, we investigate the response of mayfly species diversity to these factors in the Luvuvhu catchment, a strategic water source area in the arid northeastern region of South Africa. Mayfly larvae were sampled monthly in stones‐in‐current biotopes across 23 sites over a one‐year period. The relationship between these environmental drivers and mayfly diversity was modeled using linear mixed effects models (LMMs) and a model‐based multivariate approach. Threshold Indicator Taxa Analysis (TITAN) was used to model the response of mayfly species to important gradients and identify thresholds of change. Site‐specific characteristic were the most important predictor of mayfly diversity, and there was considerable variation over time, with mayfly diversity peaking during winter. Along this, gradient temperature was the best predictor of assemblage structure, with five out of six reliable indicator species being cold‐adapted, and a community threshold response at 19°C. Results support laboratory‐based thresholds of temperature for mayfly species survival and development, extending empirical evidence to include field‐based observations. Increased global (climate change) and local (riparian vegetation removal, impoundments) changes are predicted to have negative impacts on mayfly diversity and ultimately on ecosystem function.     

Climate change reduces offspring fitness in littoral spawners: a study integrating organismic response and long‐term time‐series

Integrating long‐term ecological observations with experimental findings on species response and tolerance to environmental stress supports an understanding of climate effects on population dynamics. Here, we combine the two approaches, laboratory experiments and analysis of multi‐decadal time‐series, to understand the consequences of climate anomalies and ongoing change for the population dynamics of a eurythermal littoral species, Carcinus aestuarii. For the generation of cause and effect hypotheses we investigated the thermal response of crab embryos at four developmental stages. We first measured metabolic rate variations in embryos following acute warming (16–24 °C) and after incubation at 20 and 24 °C for limited periods. All experiments consistently revealed differential thermal responses depending on the developmental stage. Temperature‐induced changes in metabolic activity of early embryonic stages of blastula and gastrula suggested the onset of abnormal development. In contrast, later developmental stages, characterized by tissue and organ differentiation, were marginally affected by temperature anomalies, indicating enhanced resilience to thermal stress. Then, we extended these findings to a larger, population scale, by analyzing a time‐series of C. aestuarii landings in the Venice lagoon from 1945 to 2010 (ripe crabs were recorded separately) in relation to temperature. Landings and extreme climatic events showed marked long‐term and short‐term variations. We found negative relationships between landings and thermal stress indices on both timescales, with time lags consistent with an impact on crab early life stages. When quantitatively evaluating the influence of thermal stress on population dynamics, we found that it has a comparable effect to that of the biomass of spawners. This work provides strong evidence that physiological responses to climatic anomalies translate into population‐level changes and that apparently tolerant species may be impacted before the ontogeny of eurythermy. These ontogenetic bottlenecks markedly shape population dynamics and require study to assess the effects of global change.     

Temporal environmental change, clonal physiology and the genetic structure of a Daphnia assemblage (D. galeata–hyalina hybrid species complex)

1. In a combined field and laboratory study, seasonal relationships between water temperature and oxygen content, genetic structure (composition of MultiLocus Genotypes, MLGs) of a Daphnia assemblage (D. galeata–hyalina hybrid species complex), and the physiological properties of clones of frequent MLGs were studied. In accordance with the oxygen‐limited thermal tolerance hypothesis, essential physiological variables of oxygen transport and supply were measured within the tolerable temperature range. 2. A few MLGs (types T1–T4) were frequent during early spring and late autumn at surface temperatures below 10 °C. Clones of T1–T4 showed a low tolerance towards higher temperatures (above 20 °C) and a high phenotypic plasticity under thermal acclimation in comparison to clones derived from frequent MLGs from later seasons, and stored high–medium quantities of carbohydrates at 12 and 18 °C. 3. Another MLG (T6) succeeded the MLGs T1–T4. T6 was frequent over most of the year at temperatures above 10 °C and below 20 °C. A clone derived from T6 exhibited a high tolerance towards warm temperatures and a more restricted phenotypic plasticity. It stored high–medium quantities of carbohydrates at 12, 18 and 24 °C and showed a high capacity for acclimatory adjustments based on haemoglobin expression. 4. During the summer period at temperatures ≥20 °C, the MLG T6 was found mainly near to the thermocline, where temperature and oxygen content were distinctly lower, and to a lesser extent in surface water. At the surface, another MLG (T19) was predominant during this period. A clone of this MLG showed a very high tolerance towards warm temperatures, minimal phenotypic plasticity, low carbohydrate stores and a high capacity for circulatory adjustments to improve oxygen transport at higher temperatures. 5. This study provides evidence for connections between the spatio‐temporal genetic heterogeneity of a Daphnia assemblage and the seasonal changes of water temperature and oxygen content. The data also suggest that not only the actual temperature but also the dynamics of temperature change may influence the genetic structure of Daphnia populations and assemblages.     

An alternative,low-cost method to chill water for critical thermal minima trials

Water temperature is an important abiotic factor that impacts physiological processes in fish. Attempts to quantify thermal tolerance of fishes exposed to various temperatures have been performed since the 1800s. A common approach to test the thermal tolerance of fishes is the critical thermal method. Traditionally this method has required access to large and expensive lab equipment. However, many individuals may not have direct access to such equipment, making critical thermal studies difficult-to-impossible to conduct. We present a simple and cost-friendly alternative device to use for critical thermal minima trials. This device uses a cooler with a copper line and copper coil to chill water within an aquarium. A pump and valves control the water flow as it passes from the aquarium through the copper. This allows the user to lower the water temperature in the aquarium from 28^oC to 0^oC at a steady rate of 0.23^oC min⁻¹. The device allows those with limited funding or without access to traditional lab equipment the ability to perform critical thermal minima trials, expanding our collective understanding of life histories of fish and their potential vulnerabilities to increasingly altered thermal environments.     

Low acclimation capacity of narrow‐ranging thermal specialists exposes susceptibility to global climate change

Thermal acclimation is hypothesized to offer a selective advantage in seasonal habitats and may underlie disparities in geographic range size among closely‐related species with similar ecologies. Understanding this relationship is also critical for identifying species that are more sensitive to warming climates. Here, we study North American plethodontid salamanders to investigate whether acclimation ability is associated with species’ latitudinal extents and the thermal range of the environments they inhabit. We quantified variation in thermal physiology by measuring standard metabolic rate (SMR) at different test and acclimation temperatures for 16 species of salamanders with varying latitudinal extents. A phylogenetically‐controlled Markov chain Monte Carlo generalized linear mixed model (MCMCglmm) was then employed to determine whether there are differences in SMR between wide‐ and narrow‐ranging species at different acclimation temperatures. In addition, we tested for a relationship between the acclimation ability of species and the environmental temperature ranges they inhabit. Further, we investigated if there is a trade‐off between critical thermal maximum (CTMax) and thermal acclimation ability. MCMCglmm results show a significant difference in acclimation ability between wide and narrow‐ranging temperate salamanders. Salamanders with wide latitudinal distributions maintain or slightly increase SMR when subjected to higher test and acclimation temperatures, whereas several narrow‐ranging species show significant metabolic depression. We also found significant, positive relationships between acclimation ability and environmental thermal range, and between acclimation ability and CTMax. Wide‐ranging salamander species exhibit a greater capacity for thermal acclimation than narrow‐ranging species, suggesting that selection for acclimation ability may have been a key factor enabling geographic expansion into areas with greater thermal variability. Further, given that narrow‐ranging salamanders are found to have both poor acclimation ability and lower tolerance to warm temperatures, they are likely to be more susceptible to environmental warming associated with anthropogenic climate change.     

Evolutionary and environmental determinants of freshwater fish thermal tolerance and plasticity

Understanding the extent to which phylogenetic constraints and adaptive evolutionary forces help define the physiological sensitivity of species is critical for anticipating climate‐related impacts in aquatic environments. Yet, whether upper thermal tolerance and plasticity are shaped by common evolutionary and environmental mechanisms remains to be tested. Based on a systematic literature review, we investigated this question in 82 freshwater fish species (27 families) representing 829 experiments for which data existed on upper thermal limits and it was possible to estimate plasticity using upper thermal tolerance reaction norms. Our findings indicated that there are strong phylogenetic signals in both thermal tolerances and acclimation capacity, although it is weaker in the latter. We found that upper thermal tolerances are correlated with the temperatures experienced by species across their range, likely because of spatially autocorrelated processes in which closely related species share similar selection pressures and limited dispersal from ancestral environments. No association with species thermal habitat was found for acclimation capacity. Instead, species with the lowest physiological plasticity also displayed the highest thermal tolerances, reflecting to some extent an evolutionary trade‐off between these two traits. Although our study demonstrates that macroecological climatic niche features measured from species distributions are likely to provide a good approximation of freshwater fish sensitivity to climate change, disentangling the mechanisms underlying both acute and chronic heat tolerances may help to refine predictions regarding climate change‐related range shifts and extinctions.     

Freshwater species distributions along thermal gradients

The distribution of a species along a thermal gradient is commonly approximated by a unimodal response curve, with a characteristic single optimum near the temperature where a species is most likely to be found, and a decreasing probability of occurrence away from the optimum. We aimed at identifying thermal response curves (TRCs) of European freshwater species and evaluating the potential impact of climate warming across species, taxonomic groups, and latitude. We first applied generalized additive models using catchment‐scale global data on distribution ranges of 577 freshwater species native to Europe and four different temperature variables (the current annual mean air/water temperature and the maximum air/water temperature of the warmest month) to describe species TRCs. We then classified TRCs into one of eight curve types and identified spatial patterns in thermal responses. Finally, we integrated empirical TRCs and the projected geographic distribution of climate warming to evaluate the effect of rising temperatures on species’ distributions. For the different temperature variables, 390–463 of 577 species (67.6%–80.2%) were characterized by a unimodal TRC. The number of species with a unimodal TRC decreased from central toward northern and southern Europe. Warming tolerance (WT = maximum temperature of occurrence—preferred temperature) was higher at higher latitudes. Preferred temperature of many species is already exceeded. Rising temperatures will affect most Mediterranean species. We demonstrated that freshwater species’ occurrence probabilities are most frequently unimodal. The impact of the global climate warming on species distributions is species and latitude dependent. Among the studied taxonomic groups, rising temperatures will be most detrimental to fish. Our findings support the efforts of catchment‐based freshwater management and conservation in the face of global warming.     

Environmental context alters ecological trade‐offs controlling ant coexistence in a spatially heterogeneous region

1. Ecological trade‐offs in ant (Hymenoptera: Formicidae) assemblages and their implications for coexistence boast a rich history in entomology. Yet investigations of trade‐offs have largely been limited to homogeneous environments. We examined how environmental context modifies trade‐off expression in an ant assemblage spanning a heterogeneous region in central Florida, U.S.A. 2. We examined how trade‐off expression is altered among two contrasting habitat types: open shrub and forest. We tested for the presence of the dominance‐discovery trade‐off and two dominance‐thermal tolerance trade‐offs by estimating behavioral dominance, discovery ability, and thermal tolerance (foraging thermal limit, lethal temperature, and maximal abundance temperature) for a wide range of interacting ant species. 3. We found significantly linear dominance hierarchies in both shrub and forest habitats, showing dominant species out‐compete subordinates for food resources. In thermally stressful shrub habitats, subordinates exhibit higher thermal tolerances, take greater thermal risks, and reach maximum forager abundances at higher temperatures than do dominant species. This suggests temperature mediated trade‐offs control coexistence in shrub habitat. In thermally moderate forest habitat, we found limited evidence for trade‐offs between competitive dominance and resource discovery or between dominance and thermal traits, implying other processes control coexistence. These results demonstrate that trade‐offs controlling ant coexistence may be contingent on environmental context.     

Using modelled stream temperatures to predict macro‐spatial patterns of stream invertebrate biodiversity

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Physical effects of habitat‐forming species override latitudinal trends in temperature

Latitudinal and elevational temperature gradients (LTG and ETG) play central roles in biogeographical theory, underpinning predictions of large‐scale patterns in organismal thermal stress, species' ranges and distributional responses to climate change. Yet an enormous fraction of Earth's taxa live exclusively in habitats where foundation species modify temperatures. We examine little‐explored implications of this widespread trend using a classic model system for understanding heat stresses – rocky intertidal shores. Through integrated field measurements and laboratory trials, we demonstrate that thermal buffering by centimetre‐thick mussel and seaweed beds eliminates differences in stress‐inducing high temperatures and associated mortality risk that would otherwise arise over 14° of latitude and ~ 1 m of shore elevation. These results reveal the extent to which physical effects of habitat‐formers can overwhelm broad‐scale thermal trends, suggesting a need to re‐evaluate climate change predictions for many species. Notably, inhabitant populations may exhibit deceptive resilience to warming until refuge‐forming taxa become imperiled.     

Global analysis of thermal tolerance and latitude in ectotherms

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.     

The shape of abundance distributions across temperature gradients in reef fishes

Improving predictions of ecological responses to climate change requires understanding how local abundance relates to temperature gradients, yet many factors influence local abundance in wild populations. We evaluated the shape of thermal‐abundance distributions using 98 422 abundance estimates of 702 reef fish species worldwide. We found that curved ceilings in local abundance related to sea temperatures for most species, where local abundance declined from realised thermal ‘optima’ towards warmer and cooler environments. Although generally supporting the abundant‐centre hypothesis, many species also displayed asymmetrical thermal‐abundance distributions. For many tropical species, abundances did not decline at warm distribution edges due to an unavailability of warmer environments at the equator. Habitat transitions from coral to macroalgal dominance in subtropical zones also influenced abundance distribution shapes. By quantifying the factors constraining species’ abundance, we provide an important empirical basis for improving predictions of community re‐structuring in a warmer world.     

Larval connectivity across temperature gradients and its potential effect on heat tolerance in coral populations

Coral reefs are increasingly exposed to elevated temperatures that can cause coral bleaching and high levels of mortality of corals and associated organisms. The temperature threshold for coral bleaching depends on the acclimation and adaptation of corals to the local maximum temperature regime. However, because of larval dispersal, coral populations can receive larvae from corals that are adapted to very different temperature regimes. We combine an offline particle tracking routine with output from a high‐resolution physical oceanographic model to investigate whether connectivity of coral larvae between reefs of different thermal regimes could alter the thermal stress threshold of corals. Our results suggest that larval transport between reefs of widely varying temperatures is likely in the Coral Triangle and that accounting for this connectivity may be important in bleaching predictions. This has important implications in conservation planning, because connectivity may allow some reefs to have an inherited heat tolerance that is higher or lower than predicted based on local conditions alone.     

The impact of climate change measured at relevant spatial scales: new hope for tropical lizards

Much attention has been given to recent predictions that widespread extinctions of tropical ectotherms, and tropical forest lizards in particular, will result from anthropogenic climate change. Most of these predictions, however, are based on environmental temperature data measured at a maximum resolution of 1 km², whereas individuals of most species experience thermal variation on a much finer scale. To address this disconnect, we combined thermal performance curves for five populations of Anolis lizard from the Bay Islands of Honduras with high‐resolution temperature distributions generated from physical models. Previous research has suggested that open‐habitat species are likely to invade forest habitat and drive forest species to extinction. We test this hypothesis, and compare the vulnerabilities of closely related, but allopatric, forest species. Our data suggest that the open‐habitat populations we studied will not invade forest habitat and may actually benefit from predicted warming for many decades. Conversely, one of the forest species we studied should experience reduced activity time as a result of warming, while two others are unlikely to experience a significant decline in performance. Our results suggest that global‐scale predictions generated using low‐resolution temperature data may overestimate the vulnerability of many tropical ectotherms to climate change.     

Evolutionary potential of thermal preference and heat tolerance in Drosophila subobscura

Evolutionary change of thermal traits (i.e., heat tolerance and behavioural thermoregulation) is one of the most important mechanisms exhibited by organisms to respond to global warming. However, the evolutionary potential of heat tolerance, estimated as narrow‐sense heritability, depends on the methodology employed. An alternative adaptive mechanism to buffer extreme temperatures is behavioural thermoregulation, although the association between heat tolerance and thermal preference is not clearly understood. We suspect that methodological effects associated with the duration of heat stress during thermal tolerance assays are responsible for missing this genetic association. To test this hypothesis, we estimated the heritabilities and genetic correlations for thermal traits in Drosophila subobscura, using high‐temperature static and slow ramping assays. We found that heritability for heat tolerance was higher in static assays (h² = 0.134) than in slow ramping assays (h² = 0.084), suggesting that fast assays may provide a more precise estimation of the genetic variation of heat tolerance. In addition, thermal preference exhibited a low heritability (h² = 0.066), suggesting a reduced evolutionary response for this trait. We also found that the different estimates of heat tolerance and thermal preference were not genetically correlated, regardless of how heat tolerance was estimated. In conclusion, our data suggest that these thermal traits can evolve independently in this species. In agreement with previous evidence, these results indicate that methodology may have an important impact on genetic estimates of heat tolerance and that fast assays are more likely to detect the genetic component of heat tolerance.     

Plasticity and local adaptation explain lizard cold tolerance

How does climate variation limit the range of species and what does it take for species to colonize new regions? In this issue of Molecular Ecology, Campbell‐Staton et al. ( 2018 ) address these broad questions by investigating cold tolerance adaptation in the green anole lizard (Anolis carolinensis) across a latitudinal transect. By integrating physiological data, gene expression data and acclimation experiments, the authors disentangle the mechanisms underlying cold adaptation. They first establish that cold tolerance adaptation in Anolis lizards follows the predictions of the oxygen‐ and capacity‐limited thermal tolerance hypothesis, which states that organisms are limited by temperature thresholds at which oxygen supply cannot meet demand. They then explore the drivers of cold tolerance at a finer scale, finding evidence that northern populations are adapted to cooler thermal regimes and that both phenotypic plasticity and heritable genetic variation contribute to cold tolerance. The integration of physiological and gene expression data further highlights the varied mechanisms that drive cold tolerance adaptation in Anolis lizards, including both supply‐side and demand‐side adaptations that improve oxygen economy. Altogether, their work provides new insight into the physiological and genetic mechanisms underlying adaptation to new climatic niches and demonstrates that cold tolerance in northern lizard populations is achieved through the synergy of physiological plasticity and local genetic adaptation for thermal performance.     

Thermal Buffering of Microhabitats is a Critical Factor Mediating Warming Vulnerability of Frogs in the Philippine Biodiversity Hotspot

Species may circumvent the impacts of climate warming if the habitats they use reduce ambient temperature. In this study, we identified which frog species from a tropical montane rain forest in the Philippines may be vulnerable to climate warming. To do so, we selected five anuran species that utilize four breeding habitats and identified the sensitivity and exposure of tadpoles and direct‐developer eggs to heat by measuring their critical thermal maximums (CT_max) and the habitat‐specific temperatures they experience. Our study species included two direct‐developer frogs—one species that lays its eggs on exposed leaves, and another that lays its eggs in ferns—and three species that produce aquatic free‐swimming tadpoles—two stream breeders, and one phytotelm (tree hole) breeder. We compared thermal tolerances derived from microclimates of breeding habitats with tolerances derived from macroclimate (i.e., non‐buffered air temperature taken from the rain forest canopy). We also examined whether differences in CT_max existed across life‐history stages (egg, metamorph/young‐of‐year, and adult) for the two direct‐developer frog species. Habitats buffered ambient temperature and expanded thermal tolerances of all frog species. We found that direct‐developers, however, are more vulnerable to increased temperatures than aquatic breeders—indicated by their high sensitivity to temperature, and exposure to high temperatures. Direct‐developer eggs were more sensitive to warming than both metamorph and adult life‐history stages. Thermally buffered microhabitats may represent the only protection against current and impending climate warming. Our data highlight the importance of considering sensitivity and exposure in unison when deciphering warming vulnerability of frogs.     

Thermal sensitivity of a Neotropical amphibian (Engystomops pustulosus) and its vulnerability to climate change

A species’ thermal sensitivity and its exposure to climate variation are key components in the prediction of its vulnerability to climate change. We tested the thermal sensitivity of a tropical amphibian that lives in a mild constant climate in which the thermal tolerance range is expected to closely match the experienced environmental temperature. The air temperature that this species is exposed to varies between 21.9 and 31.6°C with an annual mean of 27.2°C. We estimated the microhabitat water temperature variation under vegetation shade, which buffers the temperature by 1.8°C in relation to that of the air, and with open canopy, where the water was 1.9°C warmer than the air temperature. With broods of tadpoles split into five treatments (15°C, 21°C, 28°C, 31°C, and 33°C), we estimated the critical thermal maximum (CTMax) and critical thermal minimum (CTMin) after at least 7 days of acclimation. Both CTMax (42.3°C) and CTMin (11.8°C) were more extreme than the temperature range estimated for the field. We estimated the optimum temperature (T_o = 28.8°C) and the thermal performance breadth (range: 23.3–34.1°C) based on growth rate (g/day). The animals were able to acclimate more extensively to cold than to warm temperatures. These performance curve traits closely matched the air temperature. The estimated vulnerability varied according to the microhabitat prediction model used. The combination of tadpole data on thermal sensitivity and macro‐ and microhabitat variation provides a necessary framework to understand the effects of climate change on tropical amphibians.     

Intraspecific variation in thermal acclimation and tolerance between populations of the winter ant,Prenolepis imparis

Thermal phenotypic plasticity, otherwise known as acclimation, plays an essential role in how organisms respond to short‐term temperature changes. Plasticity buffers the impact of harmful temperature changes; therefore, understanding variation in plasticity in natural populations is crucial for understanding how species will respond to the changing climate. However, very few studies have examined patterns of phenotypic plasticity among populations, especially among ant populations. Considering that this intraspecies variation can provide insight into adaptive variation in populations, the goal of this study was to quantify the short‐term acclimation ability and thermal tolerance of several populations of the winter ant, Prenolepis imparis. We tested for correlations between thermal plasticity and thermal tolerance, elevation, and body size. We characterized the thermal environment both above and below ground for several populations distributed across different elevations within California, USA. In addition, we measured the short‐term acclimation ability and thermal tolerance of those populations. To measure thermal tolerance, we used chill‐coma recovery time (CCRT) and knockdown time as indicators of cold and heat tolerance, respectively. Short‐term phenotypic plasticity was assessed by calculating acclimation capacity using CCRT and knockdown time after exposure to both high and low temperatures. We found that several populations displayed different chill‐coma recovery times and a few displayed different heat knockdown times, and that the acclimation capacities of cold and heat tolerance differed among most populations. The high‐elevation populations displayed increased tolerance to the cold (faster CCRT) and greater plasticity. For high‐temperature tolerance, we found heat tolerance was not associated with altitude; instead, greater tolerance to the heat was correlated with increased plasticity at higher temperatures. These current findings provide insight into thermal adaptation and factors that contribute to phenotypic diversity by revealing physiological variance among populations.