Temperature and Diet Acclimation Modify the Acute Thermal Performance of the Largest Extant Amphibian

Hepatic Metabolomic Responses to Low-Temperature Stress in the Invasive Turtle, Trachemys scripta elegans

Investigating the physiological and biochemical changes of ectothermic species before entering hibernation would contribute to the understanding of how they adapt to low-temperature environments. Here, red-eared slider turtle (Trachemys scripta elegans) hatchlings were maintained under different thermal treatments (24 °C, slowly decreasing temperatures from 24 °C to 14 °C, and to 4 °C). Hepatic metabolite alterations were measured to assess the metabolic impacts of low-temperature stress in this species. Of these differentially changed metabolites, some (e.g., raffinose, spermidine, allocholic acid, taurohyocholate, 2-ketobutyric acid, acetylcysteine) were shown to decrease, while others (e.g., stearolic acid, D-mannose) increased in low-temperature treatments. Our results indicated that short-term low-temperature stress might have limited impacts on lipid and energy metabolism in this species. The changes in other metabolites (e.g., allocholic acid, taurohyocholate, spermine, acetylcysteine) might be associated with a low food intake (and thus reduced digestive performance) and weakened immune ability of low-temperature-exposed animals.

The nature of science: The fundamental role of natural history in ecology, evolution, conservation, and education

There is a contemporary trend in many major research institutions to de-emphasize the importance of natural history education in favor of theoretical, laboratory, or simulation-based research programs. This may take the form of removing biodiversity and field courses from the curriculum and the sometimes subtle maligning of natural history research as a "lesser" branch of science. Additional threats include massive funding cuts to natural history museums and the maintenance of their collections, the extirpation of taxonomists across disciplines, and a critical under-appreciation of the role that natural history data (and other forms of observational data, including Indigenous knowledge) play in the scientific process. In this paper, we demonstrate that natural history knowledge is integral to any competitive science program through a comprehensive review of the ways in which they continue to shape modern theory and the public perception of science. We do so by reviewing how natural history research has guided the disciplines of ecology, evolution, and conservation and how natural history data are crucial for effective education programs and public policy. We underscore these insights with contemporary case studies, including: how understanding the dynamics of evolutionary radiation relies on natural history data; methods for extracting novel data from museum specimens; insights provided by multi-decade natural history programs; and how natural history is the most logical venue for creating an informed and scientifically literate society. We conclude with recommendations aimed at students, university faculty, and administrators for integrating and supporting natural history in their mandates. Fundamentally, we are all interested in understanding the natural world, but we can often fall into the habit of abstracting our research away from its natural contexts and complexities. Doing so risks losing sight of entire vistas of new questions and insights in favor of an over-emphasis on simulated or overly controlled studies.

Developmental environments do not affect thermal physiological traits in reptiles: an experimental test and meta-analysis

On a global scale, organisms face significant challenges due to climate change and anthropogenic disturbance. In many ectotherms, developmental and physiological processes are sensitive to changes in temperature and resources. Developmental plasticity in thermal physiology may provide adaptive advantages to environmental extremes if early environmental conditions are predictive of late-life environments. Here, we conducted a laboratory experiment to test how developmental temperature and maternal resource investment influence thermal physiological traits (critical thermal maximum: CTmax and thermal preference: Tpref) in a common skink (Lampropholis delicata). We then compared our experimental findings more broadly across reptiles (snakes, lizards and turtles) using meta-analysis. In both our experimental study and meta-analysis, we did not find evidence that developmental environments influence CTmax or Tpref. Furthermore, the effects of developmental environments on thermal physiology did not vary by age, taxon or climate zone (temperate/tropical). Overall, the magnitude of developmental plasticity on thermal physiology appears to be limited across reptile taxa suggesting that behavioural or evolutionary processes may be more important. However, there is a paucity of information across most reptile taxa, and a broader focus on thermal performance curves themselves will be critical in understanding the impacts of changing thermal conditions on reptiles in the future.

How will warming affect the growth and body size of the largest extant amphibian? More than the temperature-size rule

Declining body size is a universal ecological response to global warming in ectotherms. Ectotherms grow faster but mature at a smaller size at higher temperatures. This phenomenon is known as the temperature-size rule (TSR). However, we know little about the details of the relationship between temperature and size. Here, this issue was studied in the Chinese giant salamander (Andrias davidianus), one of the largest extant amphibians and a flagship species of conservation in China. Warm-acclimated A. davidianus larvae (25 °C) had accelerated development but little superiority in body growth when compared to their 15 °C counterparts when fed with red worm. This predicts a drastic decrease in adult body size with warming. However, a fish diet (more abundant lipid and protein) improved the growth performance at 25 °C. The underlying mechanism was studied. Warm-acclimated larvae had enlarged livers but shortened tails (fat depot). Their livers suffered from energy deficiencies and decreased protein levels, even when protein synthesis and energy metabolism were transcriptionally upregulated. This could be a direct explanation for their poor growth performance. Further analyses revealed a metabolic disorder resembling mammal glycogen storage disease in warm-acclimated larvae, indicating deficiency in glycogen catabolism. This speculation is consistent with their increased lipid and amino acid catabolism and explained the poor energy conditions of the warm-acclimated larvae. Additionally, a deficiency in glycogen metabolism explains the different efficiency of worm and fish diets in supporting the growth of warm-acclimated larvae, even when both diets were provided sufficiently. In conclusion, our results suggest that the relationship between temperature and body size can be flexible, which is a significant finding in terms of the TSR. The underlying metabolic and nutrient mechanisms were revealed. This knowledge can help deepen our understanding of the consequences of warming and can contribute to the conservation of A. davidianus.

Rising floor and dropping ceiling: organ heterogeneity in response to cold acclimation of the largest extant amphibian

Low temperature imposes strong selective pressure on ectotherms. To maximize their overall fitness under cold conditions, the ectotherms may either try to maintain their physiological activities through metabolic compensation or enter into metabolic depression; however, some species adopt both strategies to cope with different degrees of cold. Nevertheless, how these two seemingly opposite strategies are coordinated has rarely been elucidated. Here, we investigated the molecular strategy underlying the cold acclimation of Andrias davidianus, the largest extant amphibian, using multi-organ metabolomics and transcriptomics. The results showed remarkable organ heterogeneity in response to cold. While most organs showed transcriptional upregulation of metabolic processes, the heart exhibited downregulation. This heterogeneity explained the adaptive reorganization in resource allocation, which compensates for metabolic maintenance by compromising growth. Importantly, the cardiac function might constitute a 'ceiling' to constrain the space for compensation, especially under colder conditions. Additionally, the opposite transcriptional regulation of oxidative phosphorylation and other pathways might also shape the overall metabolic capacity under cold conditions. The heterogeneity in cold responses may have directed a shift in cold adaptive strategy from compensation to depression with a drop in temperature. These results provide a novel insight into the regulatory mechanisms underlying cold survival strategies of ectotherms.