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Abstract Adaptive plasticity in thermal tolerance traits may buffer organisms against changing temperatures, making such responses of particular interest in the face of global climate change. Although population variation is integral to the evolvability of this trait, many studies inferring proxies of physiological vulnerability from thermal tolerance traits extrapolate data from one or a few populations to represent the species. Estimates of physiological vulnerability can be further complicated by methodological effects associated with experimental design. We evaluated how populations varied in their acclimation capacity (i.e., the magnitude of plasticity) for critical thermal maximum (CTmax) in two species of tailed frogs (Ascaphidae), cold‐stream specialists. We used the estimates of acclimation capacity to infer physiological vulnerability to future warming. We performed CTmax experiments on tadpoles from 14 populations using a fully factorial experimental design of two holding temperatures (8 and 15°C) and two experimental starting temperatures (8 and 15°C). This design allowed us to investigate the acute effects of transferring organisms from one holding temperature to a different experimental starting temperature, as well as fully acclimated responses by using the same holding and starting temperature. We found that most populations exhibited beneficial acclimation, where CTmax was higher in tadpoles held at a warmer temperature, but populations varied markedly in the magnitude of the response and the inferred physiological vulnerability to future warming. We also found that the response of transferring organisms to different starting temperatures varied substantially among populations, although accounting for acute effects did not greatly alter estimates of physiological vulnerability at the species level or for most populations. These results underscore the importance of sampling widely among populations when inferring physiological vulnerability, as population variation in acclimation capacity and thermal sensitivity may be critical when assessing vulnerability to future warming.
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Temperature and mass scaling affect cutaneous and pulmonary respiratory performance in a diving frog
Global climate change is altering patterns of temperature variation, with unpredictable consequences for species and ecosystems. The Metabolic Theory of Ecology (MTE) provides a powerful framework for predicting climate change impacts on ectotherm metabolic performance. MTE postulates that physiological and ecological processes are limited by organism metabolic rates, which scale predictably with body mass and temperature. The purpose of this study was to determine if different metabolic proxies generate different empirical estimates of key MTE model parameters for the aquatic frog Xenopus laevis when allowed to exhibit normal diving behavior. We used a novel methodological approach in combining a flow-through respirometry setup with the open-source Arduino platform to measure mass and temperature effects on 4 different proxies for whole-body metabolism (total O2 consumption, cutaneous O2 consumption, pulmonary O2 consumption, and ventilation frequency), following thermal acclimation to one of 3 temperatures (8°C, 17°C, or 26°C). Different metabolic proxies generated different mass-scaling exponents (b) and activation energy (EA) estimates, highlighting the importance of metabolic proxy selection when parameterizing MTE-derived models. Animals acclimated to 17°C had higher O2 consumption across all temperatures, but thermal acclimation did not influence estimates of key MTE parameters EA and b. Cutaneous respiration generated lower MTE parameters than pulmonary respiration, consistent with temperature and mass constraints on dissolved oxygen availability, SA:V ratios, and diffusion distances across skin. Our results show that the choice of metabolic proxy can have a big impact on empirical estimates for key MTE model parameters.
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- Award ID(s):
- 1651888
- PAR ID:
- 10252392
- Date Published:
- Journal Name:
- Integrative Zoology
- ISSN:
- 1749-4877
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1111/1749-4877.12551
