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Dryad

Data for: Multi-scale relationships in thermal limits within and between two cold-water frog species uncover different trends in physiological vulnerability

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Abstract

  1. Critical thermal limits represent an important component of an organism’s capacity to cope with future temperature changes. Understanding the drivers of variation in these traits may uncover patterns in physiological vulnerability to climate change. Local temperature extremes have emerged as a major driver of thermal limits, although their effects can be mediated by the exploitation of fine-scale spatial variation in temperature through behavioral thermoregulation.
  2. Here, we investigated thermal limits along elevation gradients within and between two cold-water frog species (Ascaphus spp.), one with a coastal distribution (A. truei) and the other with a continental range (A. montanus). We quantified thermal limits for over 700 tadpoles, representing multiple populations from each species. We combined local temporal and fine-scale spatial temperature data to quantify local thermal landscapes (i.e., thermalscapes), including the opportunity for behavioral thermoregulation.
  3. Lower thermal limits for either species could not be reached experimentally reached without the water freezing, suggesting that cold tolerance is <0.3℃. In contrast, upper thermal limits varied among populations, but this variation only reflected local temperature extremes in A. montanus, perhaps due to greater variation in stream temperatures across its range. Lastly, we found minimal fine-scale spatial variability in temperature, suggesting limited opportunity for behavioral thermoregulation and thus increased vulnerability to warming for all populations.
  4. By quantifying local thermalscapes, we uncovered different trends in the relative vulnerability of populations across elevation for each species. In A. truei, physiological vulnerability decreased with elevation, whereas in A. montanus, all populations were equally physiologically vulnerable. These results highlight how similar environments can differentially shape physiological tolerance and patterns of vulnerability of species, and in turn, impact their vulnerability to future warming.