Thermal acclimation is hypothesized to offer a selective advantage in seasonal habitats and may underlie disparities in geographic range size among closely-related species with similar ecologies. Understanding this relationship is also critical for identifying species that are more sensitive to warming climates. Here, we study North American plethodontid salamanders to investigate whether acclimation ability is associated with species’ latitudinal extents and the thermal range of the environments they inhabit. We quantified variation in thermal physiology by measuring standard metabolic rate (SMR) at different test and acclimation temperatures for 16 species of salamanders with varying latitudinal extents. A phylogenetically-controlled Markov chain Monte Carlo generalized linear mixed model (MCMCglmm) was then employed to determine whether there are differences in SMR between wide- and narrow-ranging species at different acclimation temperatures. In addition, we tested for a relationship between the acclimation ability of species and the environmental temperature ranges they inhabit. Further, we investigated if there is a trade-off between critical thermal maximum (CTMax) and thermal acclimation ability. MCMCglmm results show a significant difference in acclimation ability between wide and narrow-ranging temperate salamanders. Salamanders with wide latitudinal distributions maintain or slightly increase SMR when subjected to higher test and acclimation temperatures, whereas several narrow-ranging species show significant metabolic depression. We also found significant, positive relationships between acclimation ability and environmental thermal range, and between acclimation ability and CTMax. Wide-ranging salamander species exhibit a greater capacity for thermal acclimation than narrow-ranging species, suggesting that selection for acclimation ability may have been a key factor enabling geographic expansion into areas with greater thermal variability. Further, given that narrow-ranging salamanders are found to have both poor acclimation ability and lower tolerance to warm temperatures, they are likely to be more susceptible to environmental warming associated with anthropogenic climate change.
Bibliographical noteFunding Information:
We thank Bob Zink, Jeannine Cavender-Bares, and Rebecca Montgomery for helpful discussion of the ideas and feedback on earlier drafts; Angelica Sikorski, Danielle Peters, and Whitney Kroschel for field assistance; and Matt Gifford, Ben Lowe, Amy Luxbacher, Marta Lyons, Don Shepard, and Chris Smith for help at various stages of this project. A special thank you to Michael Angilletta, Catherine Wagner, and especially Jarrod Hadfield for assistance with the MCMCglmm analysis. Funding support for this work came from numerous sources including: Natural Sciences and Engineering Research Council of Canada (NSERC) Postgraduate Scholarship, University of Minnesota Graduate School Thesis Research Grant, Bell Museum of Natural History Dayton Grants, Minnesota Herpetological Society Grant in Research, University of Minnesota Conservation Biology Program Fellowship, and National Science Foundation funding DEB 0949590 to KHK. Relevant fieldwork permission was obtained for all collections and animal procedures followed University of Minnesota Animal Care guidelines.
- critical thermal maximum
- geographic range
- physiological tolerance
- standard metabolic rate