Hydric physiology and ecology of a federally endangered desert lizard.

Animals can respond to extreme climates by behaviourally avoiding it or by physiologically coping with it. We understand behavioural and physiological thermoregulation, but water balance has largely been neglected. Climate change includes both global warming and changes in precipitation regimes, so improving our understanding of organismal water balance is increasingly urgent.

Hydration and evaporative water loss of lizards change in response to temperature and humidity acclimation.

Testing acclimation plasticity informs our understanding of organismal physiology and applies to conservation management amidst our rapidly changing climate. Although there is a wealth of research on the plasticity of thermal and hydric physiology in response to temperature acclimation, there is a comparative gap for research on acclimation to different hydric regimes, as well as the interaction between water and temperature. We sought to fill this gap by acclimating western fence lizards (Sceloporus occidentalis) to experimental climate conditions (crossed design of hot or cool, dry or humid) for 8 days, and measuring cutaneous evaporative water loss (CEWL), plasma osmolality, hematocrit and body mass before and after acclimation.

Oxygen environment and metabolic oxygen demand predictably interact to affect thermal behavior in a lizard, Sceloporus occidentalis.

The climate crisis necessitates predicting how organisms respond to changing environments, but this requires understanding the mechanisms underlying thermal tolerance. The Hierarchical Mechanisms of Thermal Limitation (HMTL) hypothesis proposes that respiratory capacity and marginal stability of proteins and membranes interact hierarchically to determine thermal performance and limits. An untested prediction of the HMTL hypothesis is that behavioral anapyrexia (i.

High-Elevation Populations of Montane Grasshoppers Exhibit Greater Developmental Plasticity in Response to Seasonal Cues.

Populations of insects can differ in how sensitive their development, growth, and performance are to environmental conditions such as temperature and daylength. The environmental sensitivity of development can alter phenology (seasonal timing) and ecology. Warming accelerates development of most populations.

Introduction to the special issue-Beyond CT and CT : Advances in studying the thermal limits of reptiles and amphibians.

Two themes emerging from the special issue "Beyond CT and CT : Advances in Studying the Thermal Limits of Reptiles and Amphibians" are: (1) the need to identify mechanisms that determine the shape of thermal performance curves and (2) how these curves can be best used predictively.

The thermal ecology and physiology of reptiles and amphibians: A user's guide.

Research on the thermal ecology and physiology of free-living organisms is accelerating as scientists and managers recognize the urgency of the global biodiversity crisis brought on by climate change. As ectotherms, temperature fundamentally affects most aspects of the lives of amphibians and reptiles, making them excellent models for studying how animals are impacted by changing temperatures. As research on this group of organisms accelerates, it is essential to maintain consistent and optimal methodology so that results can be compared across groups and over time.

Thermoregulation and thermal performance of crested geckos (Correlophus ciliatus) suggest an extended optimality hypothesis for the evolution of thermoregulatory set-points.

Crested geckos (Correlophus ciliatus, formerly Rhacodactylus ciliatus) were rediscovered in New Caledonia 25 years ago and despite being common in the pet trade, there is no published information on their physiology. We measured thermoregulation (preferred body temperature, thermal set-point range, and voluntary limits) and performance (thermal performance curves [TPC] for 25 cm sprint speed and 1 m running speed) of adult and juvenile crested geckos in the laboratory to describe their thermal tolerances, differences among life stages, correlations between behavior and performance, and correlations with natural temperatures. Despite lacking special lighting or heating requirements in captivity, crested geckos displayed typical thermal biology for a lizard with no difference among life stages.

Analyzing Stress as a Multivariate Phenotype.

The stress phenotype is multivariate. Recent advances have broadened our understanding beyond characterizing the stress response in a single dimension. Simultaneously, the toolbox available to ecophysiologists has expanded greatly in recent years, allowing the measurement of multiple biomarkers from an individual at a single point in time.

Contrasting Responses of Lizards to Divergent Ecological Stressors Across Biological Levels of Organization.

It is frequently hypothesized that animals employ a generalized "stress response," largely mediated by glucocorticoid (GC) hormones, such as corticosterone, to combat challenging environmental conditions. Under this hypothesis, diverse stressors are predicted to have concordant effects across biological levels of an organism. We tested the generalized stress response hypothesis in two complementary experiments with juvenile and adult male Eastern fence lizards (Sceloporus undulatus).

High Temperature, Oxygen, and Performance: Insights from Reptiles and Amphibians.

Much recent theoretical and empirical work has sought to describe the physiological mechanisms underlying thermal tolerance in animals. Leading hypotheses can be broadly divided into two categories that primarily differ in organizational scale: 1) high temperature directly reduces the function of subcellular machinery, such as enzymes and cell membranes, or 2) high temperature disrupts system-level interactions, such as mismatches in the supply and demand of oxygen, prior to having any direct negative effect on the subcellular machinery. Nonetheless, a general framework describing the contexts under which either subcellular component or organ system failure limits organisms at high temperatures remains elusive.

Measuring behavioral thermal tolerance to address hot topics in ecology, evolution, and conservation.

Understanding the impacts of anthropogenic climate change requires knowing how animals avoid heat stress, and the consequences of failing to do so. Animals primarily use behavior to avoid overheating, but biologists' means for measuring and interpreting behavioral signs of stress require more development. Herein, we develop the measurement of behavioral thermal tolerance using four species of lizards.

Oxygen supply did not affect how lizards responded to thermal stress.

Zoologists rely on mechanistic niche models of behavioral thermoregulation to understand how animals respond to climate change. These models predict that species will need to disperse to higher altitudes to persist in a warmer world. However, thermal stress and, thus, thermoregulatory behavior may depend on atmospheric oxygen as well as environmental temperatures.

Reptile embryos are not capable of behavioral thermoregulation in the egg.

Reptile embryos have recently been observed moving within the egg in response to temperature, raising the exciting possibility that embryos might behaviorally thermoregulate analogous to adults. However, the conjecture that reptile embryos have ample opportunity and capacity to adaptively control their body temperature warrants further discussion. Using turtles as a model, we discuss the spatiotemporal constraints to movement in reptile embryos.

Physiology at near-critical temperatures, but not critical limits, varies between two lizard species that partition the thermal environment.

The mechanisms that mediate the interaction between the thermal environment and species ranges are generally uncertain. Thermal environments may directly restrict species when environments exceed tolerance limits (i.e.

Lizards fail to plastically adjust nesting behavior or thermal tolerance as needed to buffer populations from climate warming.

Although observations suggest the potential for phenotypic plasticity to allow adaptive responses to climate change, few experiments have assessed that potential. Modeling suggests that Sceloporus tristichus lizards will need increased nest depth, shade cover, or embryonic thermal tolerance to avoid reproductive failure resulting from climate change. To test for such plasticity, we experimentally examined how maternal temperatures affect nesting behavior and embryonic thermal sensitivity.

Hormonal and metabolic responses to upper temperature extremes in divergent life-history ecotypes of a garter snake.

Extreme temperatures constrain organismal physiology and impose both acute and chronic effects. Additionally, temperature-induced hormone-mediated stress response pathways and energetic trade-offs are important drivers of life-history variation. This study employs an integrative approach to quantify acute physiological responses to high temperatures in divergent life-history ecotypes of the western terrestrial garter snake (Thamnophis elegans).

Reptile Embryos Lack the Opportunity to Thermoregulate by Moving within the Egg.

Historically, egg-bound reptile embryos were thought to passively thermoconform to the nest environment. However, recent observations of thermal taxis by embryos of multiple reptile species have led to the widely discussed hypothesis that embryos behaviorally thermoregulate. Because temperature affects development, such thermoregulation could allow embryos to control their fate far more than historically assumed.

Life in the Frequency Domain: the Biological Impacts of Changes in Climate Variability at Multiple Time Scales.

Over the last few decades, biologists have made substantial progress in understanding relationships between changing climates and organism performance. Much of this work has focused on temperature because it is the best kept of climatic records, in many locations it is predicted to keep rising into the future, and it has profound effects on the physiology, performance, and ecology of organisms, especially ectothermic organisms which make up the vast majority of life on Earth. Nevertheless, much of the existing literature on temperature-organism interactions relies on mean temperatures.

Oxygen supply limits the heat tolerance of lizard embryos.

The mechanisms that set the thermal limits to life remain uncertain. Classically, researchers thought that heating kills by disrupting the structures of proteins or membranes, but an alternative hypothesis focuses on the demand for oxygen relative to its supply. We evaluated this alternative hypothesis by comparing the lethal temperature for lizard embryos developing at oxygen concentrations of 10-30%.

Temperature has species-specific effects on corticosterone in alligator lizards.

In response to conditions that threaten homeostasis and/or life, vertebrates generally increase production of glucocorticoid hormones, such as corticosterone (CORT), which induces an emergency physiological state referred to as the stress response. Given that extreme temperatures pose a threat to performance and survival, glucocorticoid upregulation might be an important component of a vertebrate ectotherm's response to extreme thermal conditions. To address this hypothesis, we experimentally examined the effects of body temperature (10, 20, 28, and 35°C; 5-h exposure) on CORT in two congeneric species of lizard naturally exposed to different thermal environments, northern and southern alligator lizards (Elgaria coerulea and Elgaria multicarinata, respectively).

Immobile and mobile life-history stages have different thermal physiologies in a lizard.

Temperature affects multiple aspects of an organism's biology and thus defines a major axis of the fundamental niche. For ectotherms, variation in the thermal environment is particularly important because most of these taxa have a limited capacity to thermoregulate via metabolic heat production. While temperature affects all life-history stages, stages can differ in their ability to respond to the thermal environment.

Extreme developmental temperatures result in morphological abnormalities in painted turtles (Chrysemys picta): a climate change perspective.

Increases in extreme environmental events are predicted to be major results of ongoing global climate change and may impact the persistence of species. We examined the effects of heat and cold waves during embryonic development of painted turtles (Chrysemys picta) in natural nests on the occurrence of abnormal shell morphologies in hatchlings. We found that nests exposed to extreme hot temperatures for >60 h produced more hatchlings with abnormalities than nests exposed to extreme hot temperatures for shorter periods, regardless of whether or not nesting females displayed abnormal morphologies.

Modeling the effects of climate change-induced shifts in reproductive phenology on temperature-dependent traits.

By altering phenology, organisms have the potential to match life-history events with suitable environmental conditions. Because of this, phenological plasticity has been proposed as a mechanism whereby populations might buffer themselves from climate change. We examine the potential buffering power of advancing one aspect of phenology, nesting date, on sex ratio in painted turtles (Chrysemys picta), a species with temperature-dependent sex determination.

Is water uptake by reptilian eggs regulated by physiological processes of embryos or a passive hydraulic response to developmental environments?

Moisture availability is critical for successful embryonic development in many organisms. In most oviparous reptiles, for example, water exchange between eggs and the surrounding environment can have substantial fitness consequences, but regulation of this process is unclear. Here, we evaluate whether water uptake by eggs of the lizard Anolis sagrei is regulated by the presence of a live embryo or is a passive hydraulic response to substrate moisture conditions.