Plasticity cannot fully compensate evolutionary differences in heat tolerance across fish species

Understanding how evolution and phenotypic plasticity contribute to variation in heat tolerance is crucial to predicting responses to warming. Here we analyze 272 thermal death time curves of 53 fish species acclimated to different temperatures and quantify their relative contributions. Analyses show that evolution and plasticity account, respectively, for 80.5 % and 12.4 % of the variation in elevation across curves, whereas their slope remained invariant. Evolutionary and plastic adaptive responses differ in magnitude, with heat tolerance increasing 0.54 ºC between species and 0.32 ºC within species for every 1 ºC increase in environmental temperatures. After successfully predicting critical temperatures under ramping conditions to validate these estimates, we show that fish populations can only partly ameliorate the impact of warming waters via thermal acclimation and this deficit in plasticity could increase as the warming accelerates.

Methods
We used the database of Coutant (1972) to study the variation given by evolution and plasticity in heat tolerance in fish and we used the database of Beitinger et al. (2000) to predict critical temperatures from experiments under ramp conditions to validate our results. We then used surface water temperature data for North American lakes collected by Sharma et al. (2015) between 1985 and 2009 to evaluate the effect of increased temperature on the vulnerability of fish. Here we provide all this the databases and the script to replicate the analyzes and figures of our work.