Interindividual plasticity in metabolic and thermal tolerance traits from populations subjected to recent anthropogenic heating

To better understand temperature's role in the interaction between local evolutionary adaptation and physiological plasticity, we investigated acclimation effects on metabolic performance and thermal tolerance among natural Fundulus heteroclitus (small estuarine fish) populations from different thermal environments. Fundulus heteroclitus populations experience large daily and seasonal temperature variations, as well as local mean temperature differences across their large geographical cline. In this study, we use three populations: one locally heated (32 degrees C) by thermal effluence (TE) from the Oyster Creek Nuclear Generating Station, NJ, and two nearby reference populations that do not experience local heating (28 degrees C). After acclimation to 12 or 28 degrees C, we quantified whole-animal metabolic (WAM) rate, critical thermal maximum (CTmax) and substrate-specific cardiac metabolic rate (CaM, substrates: glucose, fatty acids, lactate plus ketones plus ethanol, and endogenous (i.e. no added substrates)) in approximately 160 individuals from these three populations. Populations showed few significant differences due to large interindividual variation within populations. In general, for WAM and CTmax, the interindividual variation in acclimation response (log(2) ratio 28/12 degrees C) was a function of performance at 12 degrees C and order of acclimation (12-28 degrees C versus 28-12 degrees C). CTmax and WAM were greater at 28 degrees C than 12 degrees C, although WAM had a small change (2.32-fold) compared with the expectation for a 16 degrees C increase in temperature (expect 3- to 4.4-fold). By contrast, for CaM, the rates when acclimatized and assayed at 12 or 28 degrees C were nearly identical. The small differences in CaM between 12 and 28 degrees C temperature were partially explained by cardiac remodeling where individuals acclimatized to 12 degrees C had larger hearts than individuals acclimatized to 28 degrees C. Correlation among physiological traits was dependent on acclimation temperature. For example, WAM was negatively correlated with CTmax at 12 degrees C but positively correlated at 28 degrees C. Additionally, glucose substrate supported higher CaM than fatty acid, and fatty acid supported higher CaM than lactate, ketones and alcohol (LKA) or endogenous. However, these responses were highly variable with some individuals using much more FA than glucose. These findings suggest interindividual variation in physiological responses to temperature acclimation and indicate that additional research investigating interindividual may be relevant for global climate change responses in many species.

Automated summary

By investigating metabolic performance and thermal tolerance in natural Fundulus heteroclitus populations from different thermal environments, we found substantial interindividual variation in responses to acclimation at different temperatures, potentially influenced by performance at 12 and 28 degrees C.