An individual's fitness cost associated with environmental change likely depends on the rate of adaptive phenotypic plasticity, and yet our understanding of plasticity rates in an ecological and evolutionary context remains limited. We provide the first quantitative synthesis of existing plasticity rate data, focusing on acclimation of temperature tolerance in ectothermic animals, where we demonstrate applicability of a recently proposed analytical approach. The analyses reveal considerable variation in plasticity rates of this trait among species, with half-times (how long it takes for the initial deviation from the acclimated phenotype to be reduced by 50% when individuals are shifted to a new environment) ranging from 3.7 to 770.2 h. Furthermore, rates differ among higher taxa, being higher for amphibians and reptiles than for crustaceans and fishes, and with insects being intermediate. We argue that a more comprehensive understanding of phenotypic plasticity will be attained through increased focus on the rate parameter.

Potentially relevant papers were identified using the following procedure. First, we included eight papers identified by Burton et al. (2022) that were based on a search in Web of Science (see Burton et al. for procedure). Second, we conducted two searches on Google Scholar during January 2022. In the first search, we used the terms "temperature" and "rate of acclimation". The 739 hits were sorted by Google Scholar based on relevance, and the first 200 abstracts were scanned for inclusion. In the second search, we used the terms "temperature", "acclimation", "time course" and "critical". This resulted in 30200 hits, which also were sorted based on relevance, and where the first 200 abstracts were scanned for inclusion. From both these searches, decisions of inclusion at this stage were made based on whether the abstract contained information suggesting that the study organisms had been acclimated to an initial temperature for a given period of time, and then transferred to a ‘new’ temperature, after which thermal tolerance was measured on subsamples of these individuals at different points in time. The first search resulted in a total of 55 papers (none of these appeared among the last 30 scanned abstracts), whereas the second search identified an additional seven papers (the majority of relevant hits had been identified in the initial search). Finally, the reference lists of papers identified above were manually scanned for reference to additional papers not located in any of the previous searches where the titles indicated that they might contain the information required as indicated above. This resulted in a further 18 papers. Thus, a total of 88 papers were identified during this procedure. For each of these, we obtained the full paper and checked whether it presented the required data in an accessible form. Our selection criterium was that the study presented data on thermal tolerance (measured as critical temperatures (i.e. CT_max, CT_min), time to death/immobility of individuals, or mortality rate at a stressful temperature in groups of organisms) at a minimum of three time-points at and following movement from one rearing temperature to another one. Fifty-nine of the 88 papers were found to satisfy these criteria. Many of these contained data from several experiments (different species and/or different acclimation temperatures). It should be noted that we did not attempt to follow the PRISMA guidelines for meta-analyses. Our intention was to conduct a more exploratory and descriptive first quantitative synthesis of studies on rates of plasticity, that with a reasonable effort compiled sufficient amounts of data to address our main questions (1) whether the change in temperature tolerance in response to a shift in ambient temperature is best approximated by exponential or linear decay models, and (2) whether there are any phylogenetic patterns in this rate. Since these are novel questions, none of the empirical studies identified in our literature search actually address these questions themselves. Rather, individual studies typically focus on a single or a few highly related species, and data are usually presented in a descriptive manner without any formal statistical quantification of plasticity rates. Thus, there should be no reason for the actual results of a study to influence the decision to publish them. The only exception would be for studies that test for but fail to observe any acclimation response. However, even if such studies may be underrepresented in the literature, rates of acclimation cannot be calculated in such cases and thus these would have been excluded from the current study regardless. We therefore consider the risk of publication bias or procedures used for data collection in influencing our conclusions to be limited.

Burton, T., Ratikainen, I. I., & Einum, S. (2022). Environmental change and the rate of phenotypic plasticity. Global Change Biology, 28, 5337–5345. https://doi.org/10.1111/gcb.16291