Plasticity in thermal tolerance has limited potential to buffer ectotherms from global warming

Abstract

Global warming is increasing the overheating risk for many organisms, though the potential for plasticity in thermal tolerance to mitigate this risk is largely unknown. In part, this shortcoming stems from a lack of knowledge about global and taxonomic patterns of variation in tolerance plasticity. To address this critical issue, we test leading hypotheses for broad-scale variation in ectotherm tolerance plasticity using a dataset that includes vertebrate and invertebrate taxa from terrestrial, freshwater and marine habitats. Contrary to expectation, plasticity in heat tolerance was unrelated to latitude or thermal seasonality. However, plasticity in cold tolerance is associated with thermal seasonality in some habitat types. In addition, aquatic taxa have approximately twice the plasticity of terrestrial taxa. Based on the observed patterns of variation in tolerance plasticity, we propose that limited potential for behavioural plasticity (i.e. behavioural thermoregulation) favours the evolution of greater plasticity in physiological traits, consistent with the 'Bogert effect'. Finally, we find that all ectotherms have relatively low acclimation in thermal tolerance and demonstrate that overheating risk will be minimally reduced by acclimation in even the most plastic groups. Our analysis indicates that behavioural and evolutionary mechanisms will be critical in allowing ectotherms to buffer themselves from extreme temperatures.

Reversibility of developmental heat and cold plasticity is asymmetric and has long lasting consequences for adult thermal tolerance

“…In accordance with earlier studies in drosophilids, acclimation at 25°C increased heat tolerance compared with acclimation at 15°C, as measured by CT max (Hoffmann et al, 2003; but see Gunderson and Stillman, 2015, for a comprehensive analysis of thermal plasticity responses across ectotherms). The increased heat tolerance induced during developmental acclimation at 25°C was not lost when adult flies were acclimated at 15°C.…”

Interactions between rates of temperature change and acclimation affect latitudinal patterns of warming tolerance

“…Limited acclimation responses are characteristic of upper thermal limits, including CTmax (Hoffmann et al ., 2013; Gunderson and Stillman, 2015). The substantial effects of ramping rate have also been recorded in several investigations (e.g.…”

“…The second concern is understanding the way in which phenotypic plasticity varies among upper and lower critical limits and the extent to which such plasticity might affect estimates of the effects of changing environmental temperature on populations (Valladares et al ., 2014; Catullo et al ., 2015; Gunderson and Stillman, 2015). Early work suggested that systematic relationships exist between thermal limits, acclimation (as a form of phenotypic plasticity) and geographical range position and/or extent (reviewed by Gaston et al ., 2009).…”

“…Early work suggested that systematic relationships exist between thermal limits, acclimation (as a form of phenotypic plasticity) and geographical range position and/or extent (reviewed by Gaston et al ., 2009). Later studies have borne out the idea that both basal and plastic variation in upper critical limits tend to be less than that in lower critical limits in ectotherms (Araújo et al ., 2013; Gunderson and Stillman, 2015). Here too, however, complexity exists about the relationships, depending on the organisms and the environments they inhabit, and the methods adopted for investigation of these effects (Stillman, 2003; Sunday et al ., 2012; Kaspari et al ., 2015).…”

No phenotypic plasticity in nest-site selection in response to extreme flooding events

“…By contrast, consideration of phenotypic plasticity as a response to ECEs has been mostly theoretical [9][10][11][12]. Phenotypic plasticity may allow individuals to respond pre-emptively to upcoming ECEs or adapt once the extreme conditions arise through behavioural or physiological change [12][13][14]. To pre-empt future ECEs, individuals must possess a reliable cue to predict future conditions [15].…”