Enrico L. Rezende

Understanding how ectothermic animals perform under climate warming is key to predicting biodiversity responses to global change. We compiled empirical sprint speed data for 85 lizard species and fitted thermal performance curves (TPCs) using a mechanistic model capturing enzymatic and protein stability constraints. From the fitted TPC, we derived physiological traits related to the shape of the TPCs and tested whether body size, thermal environment and phylogeny predict performance. Species adapted to warmer habitats exhibited higher optimum temperatures and maximal performance values, supporting the hotter-is-better hypothesis. But warm-adapted specialists had a narrower thermal breadth and a steeper performance decrease under the highest thermal challenges than cold-adapted species. These results suggest an evolutionary trade-off between specialists and generalists, shaped by the evolutionary history. Our findings exhibit how evolutionary processes can tune performance to present climates but may limit adaptive potential to future warming.

Freshwater organisms face a dual challenge in warming waters due to increased metabolic demands and declining oxygen levels. However, the relationship between temperature, oxygen, and heat‐induced mortality in natural systems remains poorly understood. Here, we combine heat tolerance measurements in the laboratory with high‐resolution water temperature and oxygen records in the field to predict mortality of different species under natural conditions. We demonstrate this approach in three species, one crab and two fish, of the Mapocho River in central Chile, and validated predictions with a capture–recapture experiment under natural settings. Our work unequivocally shows that current water temperatures and dissolved oxygen levels can trigger mortality in some areas of the river and the watershed to which it belongs, providing a robust approach to predict when heat‐induced mortality is likely to occur. This approach offers a valuable tool for evaluating water quality and when river conditions may be stressful or restrictive for monitoring purposes and to design possible mitigation strategies.

The gut microbiome plays a fundamental role in host ecophysiology. Numerous studies have examined microbiome composition and functionality to understand the ecological and evolutionary factors shaping host–microbe interactions. However, the consequences of these patterns for animal ecology remain poorly understood. Here, we examined how variations in the gut microbiome influence fitness differences among Drosophila species sharing a common dietary niche. Using 16S rRNA gene sequencing, we analyzed the gut microbial taxonomy and predicted functional profiles of 4 Drosophila species collected in central Chile. Our results revealed a strong signal of phylosymbiosis in the microbial taxonomy, while functionality was highly redundant across the studied fly species. Functional biomarkers analysis indicated that the gut microbiome supports the nutritional requirements of D. simulans (Sturtevant), D. hydei (Sturtevant), and D. repleta (Wollaston); whereas, this was less evident in D. melanogaster (Meigen). To assess the potential contribution of the microbiome to host performance, we compared egg-to-adult viability between 2 species with the greatest physiological divergence: D. simulans and D. hydei. Notably, D. simulans exhibited significantly higher egg viability and shorter development time than D. hydei. Strikingly, the D. simulans microbiome contained more taxonomic and functional biomarkers previously demonstrated to enhance fly fitness, whereas the D. hydei microbiome harbored taxa and functions potentially detrimental to host performance. These findings suggest that the gut microbiome contributes to host fitness and may shape the evolutionary ecology of Drosophila species, with broader implications for community dynamics, including interspecific competition and species displacement.

Rivers are under intense anthropogenic pressure, leading to increases in water temperature and changes in physicochemical properties, which threaten aquatic biota. Understanding how these environmental changes affect heat tolerance in freshwater organisms is critical for assessing the status of wild populations and predicting their vulnerability under global warming scenarios. Here, we studied how body mass and heat tolerance, measured by thermal death time (TDTs) curves under normoxic and hypoxic conditions, vary among populations of the Chilean pencil catfish Trichomycterus areolatus inhabiting a Mediterranean river in central Chile. We detected significant differences in fork length, body mass and Fulton’s condition factor among populations, with fish from reference sites being significantly larger and in better condition. Although heat tolerance did not differ among populations, we found a strong effect of body mass under both normoxic and hypoxic experimental conditions. Simulations combining laboratory-derived TDTs with field-recorded water temperatures suggest that the window of vulnerability occurs at lower temperatures but over longer exposures, indicating that heat stress has chronic effects on T. areolatus. Accordingly, the cumulative survival simulation using the warmer season records is predicted to be lower in river sections with reduced levels of dissolved oxygen. While our results did not show population level differences in thermal tolerance per se, the significant effect of individual body mass may translate into varying vulnerability among populations, given their marked differences in body mass distribution. These findings highlight how the interplay between water quality, body condition and heat tolerance shapes the vulnerability of T. areolatus populations to warming. Thus, an integrated perspective is essential to properly assess the impact of global warming on wild freshwater populations.

Forecasts of vulnerability to climate warming require an integrative understanding of how species are exposed to, are damaged by, and recover from thermal stress in natural environments. The sensitivity of species to temperature depends on the frequency, duration, and magnitude of thermal stress. Thus, there is a generally recognized need to move beyond physiological metrics based solely on critical thermal limits and integrate them with natural heat exposure regimes. Here we propose the thermal load sensitivity (TLS) framework, which integrates biophysical principles for quantifying exposure with physiological principles of the dynamics of damage and repair processes in driving sublethal impacts on organisms. Building upon the established thermal death time (TDT) model, which integrates both the magnitude and duration of stress, the TLS framework attempts to disentangle the accumulation of damage and subsequent repair processes that alter responses to thermal stress. With the aid of case studies and reproducible simulation examples, we discuss how the TLS framework can be applied to enhance our understanding of the ecology and evolution of heat stress responses. These include assessing thermal sensitivity across diverse taxonomic groups, throughout ontogeny, and for modular organisms, as well as integrating additional stressors in combination with temperature. We identify critical research opportunities, knowledge gaps, and novel ways of integrating physiological measures of thermal sensitivity to improve understanding and predictions of thermal vulnerability at various scales across life.

Predicting vulnerability to global warming remains an elusive goal in thermal biology. In marine fishes, ongoing changes in distribution contrast with their apparent capacity to tolerate temperatures from 5°C up to 25°C higher than current conditions. Employing a data set of 786 upper critical temperatures across 213 species and recent theoretical developments, we provide conclusive evidence that these so‐called thermal safety margins overestimate the resilience to warming and that most species inhabit thermal conditions approaching their physiological tolerance limit. This result holds across latitudes and based on historical records, several populations have encountered stressful temperatures in the recent past. While warming tolerance remains similar across geographic regions, behavioural responses are constrained at low latitudes as distribution shifts required to encounter cooler waters are disproportionally higher in the tropics. Overall, our results illustrate how thermotolerance measures can be extrapolated to the field and used to quantify vulnerability to warming.

Thermal acclimation is presumed to affect heat tolerance, though it is unclear how this should impact populations under realistic natural conditions. In this study, we quantified how thermal acclimation affects heat tolerance landscapes in Drosophila and, as a consequence, their predicted mortality in the field based on modelling with a dynamic thermal tolerance algorithm. We measured the thermal tolerance of four Drosophila species (D. repleta, D. hydei, D. simulans and D. virilis) acclimated to five constant temperatures covering a range from 18 to 30°C. We then combined this information with field temperatures to construct dynamic tolerance landscapes for these species and examine how survival varies over the course of a year. Our analyses reveal the effect of acclimation on an ecologically relevant scale, specifically through the study of cumulative mortality under natural thermal regimes. We explore how different species respond to thermal challenges during acclimation, generally showing an increase in critical temperature (CT_max) while either reducing or maintaining constant thermal sensitivity (z). Furthermore, we show that while acclimation presents a relatively modest improvement in thermal tolerance during short ramping laboratory trials, this response becomes stronger when tolerance estimates are translated into ecologically relevant timescales, such as annual survival. Our results indicate that acclimation to warm conditions can substantially increase Drosophila thermal tolerance, contradicting the idea that thermal acclimation in ectotherms has only a minor effect. Our work applies novel approaches to studying thermal tolerance and aims to highlight the role of acclimation in ameliorating the impact of global warming.

Predicting how rising temperatures will impact different species and communities is imperative and increasingly urgent with ongoing global warming. Here, we describe how thermal–death time curves obtained in the laboratory can be combined with an envelope model to predict the mortality of freshwater fish under field conditions and their distribution limits. We analyze the heat tolerance and distribution of 22 fish species distributed across North America and demonstrate that high temperatures imposed a distribution boundary for 11 of them, employing a null model. Importantly, predicted thermal boundaries closely match the warmest suitable locality of the envelope model. Simulated warming suggests that the distribution of fish species with lower heat tolerances will be disproportionately affected by rising temperatures, and the rate of local extinctions will be higher across fish communities in warmer localities. Ultimately, our analyses illustrate how physiological information can be combined with distribution models to forecast how warming temperatures are expected to impact different species and ecological communities.

Flight initiation distance (FID), the distance at which an organism begins to flee from an approaching threat, is a major component of antipredator escape behavior and a potential indicator of threat perception in fishes. In this study, we analyzed the FID of three important rocky‐reef fish species targeted by spearfishers, which are of commercial and recreational importance. We tested predictions that FID to a diver threat increases with the following factors: (1) fish body size, (2) less restricted access regimes, and (3) increased historical fishing pressure. We studied three size ranges of three rocky‐reef fish species, in three different access regimes (i.e., open access, territorial user rights for fishery areas, no‐take marine protected areas), and in two regions (northern and central region with different levels of fishing pressure depending on the species). We conducted an ANOVA to analyze pairwise interactions. We used the mean square criterion to select the models that best explained the variation of our response variable. Our findings indicate that FID can be distinctly elucidated by factors such as individual size, species, access regimes, and regions. Additionally, our models show that interactions involving regions and either species or size further contribute to explain FID variability. FID was higher in larger fishes and those of higher commercial value, outside marine reserves and in the region with the highest historical fishing pressures (based on landings data). This study supports the predictions that increased FID is associated with the threat posed by spearfishing activities. Furthermore, our findings indicate that spearfishing may already be altering the behavior of rocky‐reef fishes on the north‐central coast of Chile.

Understanding how evolution and phenotypic plasticity contribute to variation in heat tolerance is crucial to predicting responses to warming. Here, we analyze 272 thermal death time curves of 53 fish species acclimated to different temperatures and quantify their relative contributions. Analyses show that evolution and plasticity account, respectively, for 80.5% and 12.4% of the variation in elevation across curves, whereas their slope remained invariant. Evolutionary and plastic adaptive responses differ in magnitude, with heat tolerance increasing to 0.54 °C between species and 0.32 °C within species for every 1 °C increase in environmental temperatures. After successfully predicting critical temperatures under ramping conditions to validate these estimates, we show that fish populations can only partly ameliorate the impact of warming waters via thermal acclimation, and this deficit in plasticity could increase as the warming accelerates.