Trade-offs between baseline thermal tolerance and thermal tolerance plasticity are much less common than it appears

Abstract

Thermal tolerance plasticity is a core mechanism by which organisms can mitigate the effects of climate change. As a result, there is a need to understand how variation in tolerance plasticity arises. The Baseline Tolerance/Plasticity Trade-off Hypothesis (hereafter referred to as the Trade-off Hypothesis, TOH) has recently emerged as a potentially powerful explanation. The TOH posits that organisms with high baseline thermal tolerance have reduced thermal tolerance plasticity relative to those with low baseline tolerance. Many studies have found support for the TOH. However, this support must be regarded cautiously because the most common means of testing the TOH can yield spurious "trade-offs" due to regression to the mean. I acquired data for 25 previously-published analyses that supported the TOH at the intraspecific level and reanalyzed them after applying a method that adjusts plasticity estimates for regression to the mean. Only four of the 25 analyses remained statistically significant after adjustment, and effect size and variance explained decreased in all cases. The few data sets in which support for the TOH was maintained after adjustment point to areas of future study, but are too few to make generalizations at this point. In sum, regression to the mean has led to a substantial overestimation of support for the TOH and must be accounted for in future tests of the hypothesis.

Thermal Tolerance Plasticity and Dynamics of Thermal Tolerance inEublepharis macularius: Implications for Future Climate-Driven Heat Stress

“…In fact, we found that individuals with relatively low basal CT max did not exhibit greater change in CT max and vice versa across the 3h and 6h time-interval treatment groups. Although comparative studies of heat hardening capacity across squamates are lacking, heat hardening capacity in different lizard species have generally rejected the TOH with the exception of two tropical species, Lampropholis coggeri (Phillips et al, 2016; Gunderson, 2023) and Hemidactylus frenatus (Lapwong et al, 2021). Furthermore, the TOH also vary in its support across other taxa of ectotherms.…”

“…Furthermore, the TOH also vary in its support across other taxa of ectotherms. For example, one species of crustaceans has shown strong support for the TOH across multiple studies, whereas two fish species have shown no support for the TOH (Gunderson, 2023). Differences in the trade-off between thermal tolerance and plasticity across and within species could be caused by different mechanisms of selection (i.e., correlational, opposing) for these two traits based on the organism's native environment (van Heerwaarden & Kellermann, 2020).…”

“…The consequence of this hypothesis is that species cannot evolve both high thermal tolerance and high plasticity in response to extreme temperatures (van Heerwaarden & Kellermann, 2020). The TOH has recently been debated to be supported across and within different lizard species because not all species show a negative correlation between heat hardening capacity and basal upper thermal tolerance (Gunderson, 2023), which suggests that other factors may be influencing variation in thermal tolerance plasticity. Data on heat hardening are available for an extremely limited number of lizard species (only six species out of the 7,641 species described, Uetz et al, 2023) (Phillips et al, 2016;Deery et al, 2021;Gilbert & Miles, 2019;Lapwong et al, 2021).…”