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

Abstract

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. the fundamental niche). However, thermal environments might also differentially affect relative performance among species prior to fundamental tolerances being met (i.e. the realized niche). We examined stress physiology (plasma glucose and corticosterone), mitochondrial performance and the muscle metabolome of congeneric lizards that naturally partition the thermal niche, Elgaria multicarinata (southern alligator lizards; SALs) and Elgaria coerulea (northern alligator lizards; NALs), in response to a thermal challenge to quantify variation in physiological performance and tolerance. Both NAL and SAL displayed physiological stress in response to high temperature, but neither showed signs of irreversible damage. NAL displayed a higher baseline mitochondrial respiration rate than SAL. Moreover, NAL substantially adjusted their physiology in response to thermal challenge, whereas SAL did not. For example, the metabolite profile of NAL shifted with changes in key energetic molecules, whereas these were unaffected in SAL. Our results indicate that near-critical high temperatures should incur greater energetic cost in NAL than SAL via an elevated metabolic rate and changes to the metabolome. Thus, SAL displace NAL in warm environments that are within NAL's fundamental thermal niche, but relatively costly. Our results suggest that subcritical thermal events can contribute to biogeographic patterns via physiological differences that alter the relative costs of living in warm or cool environments.

Phylogeography of the Northern Alligator Lizard (Squamata, Anguidae): Hidden diversity in a western endemic

“…This oddity may be explained by the physiological tolerances of E. coerulea . As in sympatric salamanders, the Northern Alligator Lizard may be more susceptible to heat stress at the higher temperatures and more arid conditions typically favoured by other squamate reptiles (Telemeco & Addis, ; Telemeco et al, ). One pattern that E. coerulea does share with many squamate reptiles is a signature of recent expansion into the Pacific Northwest (see Feldman & Spicer, ; Rodriguez‐Robles et al, ), as exemplified by a lack of genetic substructure in the northern reaches of its distribution.…”

“…While geology and timing are likely major factors in shaping the southern range limits of E. coerulea , the presence of a second, wide‐ranging alligator lizard species, E. multicarinata , may have also played a role. Although E. coerulea and E. multicarinata differ in their environmental tolerances ( E. coerulea tolerating cooler temperatures and E. multicarinata warmer temperatures), they actually have similar physiological preferences (Telemeco & Addis, ; Telemeco et al, ) and would be expected to prefer the same thermal microclimates. However, E. multicarinata is much larger and more aggressive (Nussbaum et al, ; Stebbins, ) and thus may exclude the smaller E. coerulea from occupying portions of Central and Southern California that are physiologically preferable for both species.…”

“…Throughout its distribution, E. coerulea is associated with cooler and generally more mesic forest communities (Nussbaum et al, ; St. John, ; Stebbins, ), ranging along the Pacific Coast, from Monterey Bay northward to British Columbia, and in the interior from the Sierra Nevada north where it bypasses the drier Colombia Plateau and extends eastward into Western Montana (Figure ). Although alligator lizards ( Elgaria ) are typically absent from hot and arid environments, the Northern Alligator Lizard appears more cold tolerant than other western species (Telemeco & Addis, ; Telemeco et al, ). The taxon is capable of dealing with cooler temperatures than other sympatric lizards, displaying less physiological stress and remaining active at lower temperatures than even other Elgaria species (Telemeco & Addis, ).…”

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

“…Some evidence points to such a mechanism playing an important role in early animal evolution, notably in the transition to air breathing (Berner et al 2007;Giomi et al 2014;Teague et al 2017). However, the few studies exposing animals to high temperatures and measuring indicators of aerobic and anaerobic respiration fail to find evidence for oxygen limitation in adult reptiles and amphibians (Carey 1979;Overgaard et al 2012;Fobian et al 2014;Gangloff et al 2016;Telemeco et al 2017). For example, oxygen consumption (ܸ ሶ O 2 ) by pythons (Python regius) did not plateau at temperatures approaching CT MAX either when at rest or during periods of high metabolic demand (Fobian et al 2014, Fig. 1), and resting oxygen consumption in garter snakes (Thamnophis elegans) increased with temperature with no apparent limit when animals experienced near-lethal temperatures (Gangloff et al 2016).…”

Will Danford’s Lizard Become Extinct in the Future?

“…Reduction in and extinction of reptile populations has occurred in some parts of the world and climate change is one of the reasons for explaining this decline [11]. Recent studies suggest that lizards will be affected by climate change and that the risk of extinction of lizards toward the end of the century is likely [7,[12][13][14]. According to Sinervo et al [13], climate change will cause the extinction of 40% of all global lizard populations and 56% of European Lacertidae by 2080.…”