Geographic variation and thermal plasticity shape salamander metabolic rates under current and future climates

Predicted changes in global temperature are expected to increase extinction risk for ectotherms, primarily through increased metabolic rates. Higher metabolic rates generate increased maintenance energy costs which are a major component of energy budgets. Organisms often employ plastic or evolutionary (e.g., local adaptation) mechanisms to optimize metabolic rate with respect to their environment. We examined relationships between temperature and standard metabolic rate across four populations of a widespread amphibian species to determine if populations vary in metabolic response and if their metabolic rates are plastic to seasonal thermal cues. Populations from warmer climates lowered metabolic rates when acclimating to summer temperatures as compared to spring temperatures. This may act as an energy saving mechanism during the warmest time of the year. No such plasticity was evident in populations from cooler climates. Both juvenile and adult salamanders exhibited metabolic plasticity. Although some populations responded to historic climate thermal cues, no populations showed plastic metabolic rate responses to future climate temperatures, indicating there are constraints on plastic responses. We postulate that impacts of warming will likely impact the energy budgets of salamanders, potentially affecting key demographic rates, such as individual growth and investment in reproduction.

Repeatability of water loss and gain rates of Plethodon cinereus

Water loss and gain rates of amphibians are important to understanding their ecology, especially for plethodontid salamanders. We report the first estimates of repeatability of relative water loss and gain rates of the two major colour morphs of the Eastern Red-backed Salamander, Plethodon cinereus, in the fall and spring seasons. Repeatability of relative water loss in P. cinereus was >0 in the fall but not in the spring. Repeatability of relative water gain was significant for all salamanders pooled in the fall, and was not repeatable in the spring. There were no apparent differences in repeatability of relative water loss or gain between the two colour morphs. Our results suggest that the repeatability of relative water loss and gain rates varies by season, but not by colour morph.

Integrative developmental biology in the age of anthropogenic change

Humans are changing and challenging nature in many ways. Conservation Biology seeks to limit human impacts on nature and preserve biological diversity. Traditionally, Developmental Biology and Conservation Biology have had nonoverlapping objectives, operating in distinct spheres of biological science. However, this chasm can and should be filled to help combat the emerging challenges of the 21st century. The means by which to accomplish this goal were already established within the conceptual framework of evo- and eco-devo and can be further expanded to address the ways that anthropogenic disturbance affect embryonic development. Herein, I describe ways that these approaches can be used to advance the study of reptilian embryos. More specifically, I explore the ways that a developmental perspective can advance ongoing studies of embryonic physiology in the context of global warming and chemical pollution, both of which are known stressors of reptilian embryos. I emphasize ways that these developmental perspectives can inform conservation biologists trying to develop management practices that will address the complexity of challenges facing reptilian embryos.

Terrestrial Salamanders Maintain Habitat Suitability under Climate Change despite Trade-Offs between Water Loss and Gas Exchange

Physiological acclimation has the potential to improve survival during climate change by reducing sensitivity to warming. However, acclimation can produce trade-offs due to links between related physiological traits. Water loss and gas exchange are intrinsically linked by the need for respiratory surfaces to remain moist. As climates warm and dry, organisms may attempt to lower desiccation risk by limiting water loss but at a cost of inhibiting their ability to breathe. Here we used laboratory experiments to evaluate the trade-off between water loss and gas exchange in a fully terrestrial, lungless salamander (Plethodon metcalfi). We measured acclimation of resistance to water loss and metabolic rates in response to long-term exposure to temperature and humidity treatments. We then integrated the trade-off into a simulation-based species distribution model to determine the consequences of ignoring physiological trade-offs on energy balance and aerobic scope under climate change. In the laboratory, we found a close association between acclimation of resistance to water loss and metabolic rates indicative of a trade-off. After incorporating the trade-off into our simulations, we found that energy balance and aerobic scope were reduced by 49.7% and 34.3%, respectively, under contemporary climates across their geographic range. Under future warming scenarios, incorporating the trade-off lowered the number of sites predicted to experience local extirpation by 52.2% relative to simulations without the trade-off; however, the number of sites capable of supporting the energetic requirements for reproduction declined from 44.6% to 32.6% across the species' geographic range. These experiments and simulations suggest that salamanders can maintain positive energy balance across their geographic range under climate change despite the costs associated with trade-offs between water loss and gas exchange.

Janzen's Hypothesis Meets the Bogert Effect: Connecting Climate Variation, Thermoregulatory Behavior, and Rates of Physiological Evolution

Understanding the motors and brakes that guide physiological evolution is a topic of keen interest, and is of increasing importance in light of global climate change. For more than half a century, Janzen’s hypothesis has been used to understand how climatic variability influences physiological divergence across elevation and latitude. At the same time, there has been increasing recognition that behavior and physiological evolution are mechanistically linked, with regulatory behaviors often serving to dampen environmental selection and stymie evolution (a phenomenon termed the Bogert effect). Here, we illustrate how some aspects of Janzen’s hypothesis and the Bogert effect can be connected to conceptually link climate, behavior, and rates of physiological evolution in a common framework. First, we demonstrate how thermal heterogeneity varies between nighttime and daytime environments across elevation in a tropical mountain. Using data from Hispaniolan Anolis lizards, we show how clinal variation in cold tolerance is consistent with thermally homogenous nighttime environments. Elevational patterns of heat tolerance and the preferred temperature, in contrast, are best explained by incorporating the buffering effects of thermoregulatory behavior in thermally heterogeneous daytime environments. In turn, climatic variation and behavior interact to determine rates of physiological evolution, with heat tolerance and the preferred temperature evolving much more slowly than cold tolerance. Conceptually bridging some aspects of Janzen’s hypothesis and the Bogert effect provides an integrative, cohesive framework illustrating how environment and behavior interact to shape patterns of physiological evolution.

Evaluation of the combined temperature and relative humidity preferences of the Colombian terrestrial salamander Bolitoglossa ramosi (Amphibia: Plethodontidae)

Temperature and humidity are critical factors for terrestrial lungless salamanders, as their body temperatures are largely determined by the environmental temperature and require moisture to sustain cutaneous respiration. Herein, we evaluated the preference of Bolitoglossa ramosi Brame and Wake, 1972 between a high temperature and a high relative humidity (RH), the influence of temperature on RH preferences, and the influence of RH on the thermal preferences. This study was performed in a field location in the municipality of Líbano, Tolima, Colombia. There, on different nights, we collected 84 adult B. ramosi and carried out the preference experiments, using aluminum troughs with different thermal and RH gradients. We found that between high temperature and high RH, B. ramosi preferred high RH. However, B. ramosi selected high temperatures when the gradient had a high RH and low temperatures when the gradient had a low RH. These results show that B. ramosi is able to thermoregulate and hydroregulate. Nevertheless, hydroregulation seems to be more important than thermoregulation because B. ramosi always selected the high RH gradients, while their thermal selection relied on the hydric environment.