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California halibut (Paralichthys californicus) is a candidate species for aquaculture and stock enhancement. These applications rely on sex control, either to maximize the production of faster growing females or to match sex ratios in the wild. Other paralichthids exhibit temperature‐dependent sex determination (TSD), but the presence and pattern of TSD is not well defined in California halibut. Juvenile California halibut were cultured at three distinct temperatures (15°C, 19°C, and 23°C) through the developmental period presumed to be thermosensitive based on findings from congeners. Sex ratios were quantified in each treatment using phenotypic sex identification techniques applied early (molecular biomarkers; 51–100 mm total length [TL]) and late (visual examination of the gonads; ≥100 mm TL) in the juvenile phase. Both techniques indicated similar sex determination trends at each temperature, with overall sex ratios assessed as 49.9% male at 15°C, 74.5% male at 19°C, and 98.2% male at 23°C. Growth rates were highest at 23°C and lowest at 15°C, with intrinsically fast‐ and slow‐growing individuals at all temperatures. At 15°C and 19°C, females comprised a higher proportion among the fast growers than they did among the slow growers. These data show that California halibut exhibit TSD, with temperatures of 19°C and 23°C masculinizing fish while 15°C appears to produce a 1:1 sex ratio. This study will help optimize sex ratios and growth in hatcheries through thermal manipulation. Furthermore, the developed biomolecular tools and identified temperature thresholds will be important in future work to understand the influence of global warming on wild population demographics. Research Highlights: California halibut exhibit temperature‐dependent sex determination.Rearing at 15°C produced an equal sex ratio, while exposure to higher temperatures (19°C and 23°C) caused masculinization.Expression of sex‐related genes (amh, cyp19a1a, foxl2) can be used to identify phenotypic sex. [ABSTRACT FROM AUTHOR]

Common wall lizards (Podarcis muralis) in Italy show a striking variation in body coloration across the landscape, with highly exaggerated black and green colors in hot and dry climates and brown and white colors in cool and wet climates. Males are more intensely colored than females, and previous work has suggested that the maintenance of variation in coloration across the landscape reflects climatic effects on the strength of male–male competition, and through this sexual selection. However climatic effects on the intensity of male–male competition would need to be exceptionally strong to fully explain the geographic patterns of color variation. Thus, additional processes may contribute to the maintenance of color variation. Here we test the hypothesis that selection for green and black ornamentation in the context of male–male competition is opposed by selection against ornamentation because the genes involved in the regulation of coloration have pleiotropic effects on thermal physiology, such that ornamentation is selected against in cool climates. Field observations revealed no association between body coloration and microhabitat use or field active body temperatures. Consistent with these field data, lizards at the extreme ends of the phenotypic distribution for body coloration did not show any differences in critical minimum temperature, preferred body temperature, temperature‐dependent metabolic rate, or evaporative water loss when tested in the laboratory. Combined, these results provide no evidence that genes that underlie sexual ornamentation are selected against in cool climate because of pleiotropic effects on thermal biology. Research Highlights: Common wall lizards in Italy show a striking variation in coloration across the landscape with highly exaggerated coloration occurring in hot and dry climates.This could be because climate selects for coloration in warm climates and/or because the genes that underlie.We show that there are no differences in thermal traits between lizards with different color phenotypes providing limited evidence for the antagonistic pleiotropy hypothesis. [ABSTRACT FROM AUTHOR]

Wildfires cause significant changes in natural habitats and can impact lizard populations. Through changes in the thermal environment, reduced prey availability, and increased exposure to parasite vectors, wildfires affect lizard physiology, immunity, and health. We sampled 56 Tropidurus oreadicus lizards from Cerrado savannas of Brazil living in two adjacent sites: one burned 14 days before the study, and the other unburned for 6 years. We logged the air temperatures of those sites throughout fieldwork. We assessed the short‐term possible homeostatic imbalances caused by the fires via measuring body mass, circulating levels of corticosterone (CORT), leukocytes profile changes in heterophile‐lymphocyte ratios (HLRs), innate immunity using the bacterial killing assay (BKA), and the diagnosis of hemoparasites using molecular techniques. The air temperature was significantly higher in the burned site. There was no difference in lizard body mass between the two sites, suggesting that prey availability was not affected by the wildfire. While parasite presence was seemingly not affected by fire, the timing of initial parasite infection for animals in the study was unknown, so we also evaluated parasitism as an independent variable relative to the other metrics. Our results showed that parasitic infections lead to reduced bactericidal capacity and body mass in lizards, suggesting clinical disease and depletion of innate immune resources. Moreover, we observed increased HLR with fire and parasitic infections and a strong negative correlation with BKA. These findings suggest that the increased environmental temperature following wildfires may lead to increased CORT and decreased BKA. Research highlights: The main short‐term effect of fire on these lizards appears to be changes related to thermal physiology.Animals recently exposed to wildfires had increased circulating glucocorticoid levels and reduced bactericidal capacity.Heterophile‐lymphocyte ratios (HLR) were higher in wildfire sites and animals with hemoparasite infections.The HLR was negatively correlated with bacterial killing capacity, and this relationship varied depending on exposure to wildfireCirculating corticosterone levels were elevated in response to wildfire but were not related to the presence of a hemoparasite infection.Hemoparasite infections caused by haemosporidians can lead to decreased body mass and bactericidal capacity in lizards.Wildfires may not affect Tropidurus oreadicus prey availability as lizards did not show a significant difference in body mass between recently burned and unburned areas.Wildfires do not appear to influence hemoparasite prevalence in T. oreadicus lizards in the short term.Environmental temperatures were higher at wildfire sites after the burn, which along with other habitat changes, may lead to some of the observed physiological changes. [ABSTRACT FROM AUTHOR]

Ectotherms depend on temperature to maintain their physiological functions and through behavioral changes, they can avoid overheating in their habitats. The voluntary thermal maximum (VTMax) represents the maximum temperature tolerated by individuals before actively moving to a colder place. However, if and how VTMax might change after capture and in captivity remains understudied. We investigate if measurements taken in captivity are a good proxy for thermal tolerance of wild individuals. As thermal history has been shown to affect behavioral response and physiological parameters, herein we hypothesized that VTMax of the neotropical viper Bothrops pauloensis varies throughout the captivity period. We measured the VTMax of individuals immediately after capture and in three trials during a short‐term period in captivity. Measurements were done by recording their body temperature at which they exited a heating box experimental setup. In contrast to our hypothesis, the VTMax was not significantly affected by time in captivity but there was interindividual variation. There were also no significant differences between field and captivity measurements, in spite of the small effect size. Our results indicate that the VTMax of this snake population is not affected by a short‐term captivity period. Furthermore, an invariant VTMax might indicate low phenotypic plasticity, as individuals do not appear to adjust their tolerance to short‐term exposure to higher temperatures and potential vulnerability to threats such as global warming. We expect that our results can contribute to understanding the effect of captivity on thermal tolerance in neotropical squamates, allowing for insights into their thermal physiology and ecology. Highlights: The invariant voluntary thermal maximum implies a hardwired thermal tolerance, not affected by capture and short‐term captivity.Measurements taken during a short‐captivity period might be a good proxy for behavioral thermal tolerance of individuals in the wild.There was low phenotypic plasticity but a significant interindividual variation, which might be important for population dynamics and thermal ecology. [ABSTRACT FROM AUTHOR]

Countergradient variation has been detected in diverse taxa. In a common manifestation, individuals from colder environments develop faster than conspecifics from warmer environments when placed in a common garden. Where such a pattern exists, it implies a trade‐off: Individuals from warmer environments have intrinsic rates of development lower than those demonstrated by other individuals of the same species. We explored a trade‐off between development rate and locomotor performance in the wood frog (Rana sylvatica), an amphibian for which countergradient variation has been well documented. We reared wood frogs from 10 populations under two temperature regimes, bracketing the temperatures observed in local natural ponds. Individuals reared under warmer conditions developed more rapidly but exhibited burst speeds 20% lower than individuals reared under colder conditions. The slope of the reaction norm was consistent across the 10 populations and thus, we found no evidence of countergradient variation in performance. Burst speed assays of wild‐caught tadpoles from the same populations showed a similar but nonsignificant trend, with greater variability among ponds. Overall, our findings support the existence of a development–performance trade‐off that may be of broad importance and which may help explain the widespread occurrence of countergradient variation. Research Highlights: Rapid development is associated with reductions in performance in wood frog tadpoles. This trade‐off is consistent in individuals from 10 pond populations and may explain countergradient variation in development rate reported in wood frogs and other ectotherms. [ABSTRACT FROM AUTHOR]

Ectothermic animals, such as amphibians and reptiles, are particularly sensitive to rapidly warming global temperatures. One response in these organisms may be to evolve aspects of their thermal physiology. If this response is adaptive and can occur on the appropriate time scale, it may facilitate population or species persistence in the changed environments. However, thermal physiological traits have classically been thought to evolve too slowly to keep pace with environmental change in longer‐lived vertebrates. Even as empirical work of the mid‐20th century offers mixed support for conservatism in thermal physiological traits, the generalization of low evolutionary potential in thermal traits is commonly invoked. Here, we revisit this hypothesis to better understand the mechanisms guiding the timing and patterns of physiological evolution. Characterizing the potential interactions among evolution, plasticity, behavior, and ontogenetic shifts in thermal physiology is critical for accurate prediction of how organisms will respond to our rapidly warming world. Recent work provides evidence that thermal physiological traits are not as evolutionarily rigid as once believed, with many examples of divergence in several aspects of thermal physiology at multiple phylogenetic scales. However, slow rates of evolution are often still observed, particularly at the warm end of the thermal performance curve. Furthermore, the context‐specificity of many responses makes broad generalizations about the potential evolvability of traits tenuous. We outline potential factors and considerations that require closer scrutiny to understand and predict reptile and amphibian evolutionary responses to climate change, particularly regarding the underlying genetic architecture facilitating or limiting thermal evolution. Research Highlights: Here, we review how interactions among evolution, plasticity, behavior, and ontogeny shape thermal physiological traits in reptiles and amphibians, finding that these traits are not as evolutionarily rigid as once believed across phylogenetic scales. [ABSTRACT FROM AUTHOR]

As climate change marches on, rapidly rising temperatures shatter records every year, presenting ever‐growing physiological challenges to organisms worldwide. Ectotherms rely on behavioral and physiological plasticity to contend with environmental fluctuations. Nonetheless, our understanding of thermal plasticity has been largely limited to laboratory settings. Here, we test whether aspects of thermal physiology respond to interannual shifts in thermal environment in a natural population of Phrynosoma orbiculare, a montane horned lizard, from Hidalgo, Mexico. At our field site, 2019 was markedly warmer than the year that preceded it. We detected population‐level increases in three key thermal physiological traits: preferred temperature, the critical thermal minimum, and the critical thermal maximum. Thus, thermal phenotypes appear to shift in tandem in response to environmental fluctuations. A subset of individuals were resampled across years, allowing insight into plastic shifts within an organism's lifetime. We detected parallel increases in these lizards for the preferred temperature and the critical thermal minimum, but not for the critical thermal maximum. Our results support a growing body of literature indicating that preferred conditions and cold tolerance can be highly labile over the course of an organism's lifetime, whereas hardening over shorter time periods is more common for heat tolerance. Given that heat tolerance increased at the population‐level, but not in resampled individuals, it is possible that rapid evolution occurred due to temperature increases. In short, physiological shifts can be observed in natural populations over relatively short timespans, and these shifts might reflect a combination of evolutionary and acclimatory responses. Highlights: As climate change marches on, environmental temperatures are increasing annually. We detected thermal physiological changes to interannual shifts in increasing environmental temperatures in a natural population of Phrynosoma orbiculare. [ABSTRACT FROM AUTHOR]