Feeling the heat: variation in thermal sensitivity within and among populations

Abstract

Physiology defines individual responses to global climate change and species distributions across environments. Physiological responses are driven by temperature on three timescales: acute, acclimatory and evolutionary. Acutely, passive temperature effects often dictate an expected two-fold increase in metabolic processes for every 10°C change in temperature (Q10). Yet, these acute responses often are mitigated through acclimation within an individual or evolutionary adaptation within populations over time. Natural selection can influence both responses and often reduces interindividual variation towards an optimum. However, this interindividual physiological variation is not well characterized. Here we quantified responses to a 16°C temperature difference in six physiological traits across nine thermally distinct Fundulus heteroclitus populations. These traits included whole animal metabolism (WAM), critical thermal maximum (CTmax), and substrate-specific cardiac metabolism measured in approximately 350 individuals. Traits exhibit high variation among both individuals and populations. Thermal sensitivity (Q10) was determined, specifically as the acclimated Q10, in which individuals were both acclimated and assayed at each temperature. The interindividual variation in Q10, is unexpectedly large: ranging from 0.6 to 5.4 for WAM. Thus, with a 16°C difference, metabolic rates are unchanged in some individuals, while in others are 15-fold higher. Furthermore, a significant portion of variation is related to habitat temperature. Warmer populations have a significantly lower Q10 for WAM and CTmax after acclimation. These data suggest that individual variation in thermal sensitivity reflects different physiological strategies to respond to temperature variation, providing many different adaptive responses to changing environments.

“Bet hedging” against climate change in developing and adult animals: roles for stochastic gene expression, phenotypic plasticity, epigenetic inheritance and adaptation

“…Above CT max is a temperature zone of ecological death in which animals are non-functional, if not actually dying. Certainly, CT max is subject to selection (Morgan et al, 2020;DeLiberto et al, 2022), with animals responding to long-term temperature stress in the form of higher average environmental temperatures (that is, 'climate') leading to an adaptation-in this instance, a higher CT max embedded in the population. For example, such adaptations over multiple generations occurs in Daphnia magna (Cuenca Cambronero et al, 2018).…”

Transcriptional Profiling of Populations in the Clam Ruditapes decussatus Suggests Genetically Determined Differentiation in Gene Expression along Parallel Temperature Gradients and between Races of the Atlantic Ocean and West Mediterranean Sea

“…Changes in the marine environment caused by an increase in CO 2 levels in the atmosphere, mainly an increased water temperature and a reduced pH, have led to a growing interest in the physiological and molecular mechanisms that marine organisms can employ to face these changes [1][2][3][4][5]. In addition to traditional physiological and molecular Fishes 2023, 8, 203 2 of 24 biology approaches, genomic techniques play an important role in studying the interactions between organisms and the changing environment [1].…”

Transcriptional profiling of populations in the clamRuditapes decussatussuggests genetically determined differentiation in gene-expression along parallel temperature gradients and between races of the Atlantic Ocean and West Mediterranean sea

“…The changes in the marine environment caused by the increase of CO2 in the atmosphere, mainly increased water temperature and reduced pH, have led to a growing interest in the physiological and molecular mechanisms that marine organisms can employ to face those changes [1][2][3][4][5]. In addition to traditional physiological and molecular biology approaches, genomic techniques are playing an important role in studying the interactions between organisms and the changing environment [1].…”