Abstract
Many ectothermic animals can respond to changes in their environment by altering the sensitivities of physiological rates, given sufficient time to do so. In other words, thermal acclimation and developmental plasticity can shift thermal performance curves so that performance may be completely or partially buffered against the effects of environmental temperature changes. Plastic responses can thereby increase the resilience to temperature change. However, there may be pronounced differences between individuals in their capacity for plasticity, and these differences are not necessarily reflected in population means. In a bet-hedging strategy, only a subsection of the population may persist under environmental conditions that favour either plasticity or fixed phenotypes. Thus, experimental approaches that measure means across individuals can not necessarily predict population responses to temperature change. Here, we collated published data of 608 mosquitofish (Gambusia holbrooki) each acclimated twice, to a cool and a warm temperature in random order, to model how diversity in individual capacity for plasticity can affect populations under different temperature regimes. The persistence of both plastic and fixed phenotypes indicates that on average, neither phenotype is selectively more advantageous. Fish with low acclimation capacity had greater maximal swimming performance in warm conditions, but their performance decreased to a greater extent with decreasing temperature in variable environments. In contrast, the performance of fish with high acclimation capacity decreased to a lesser extent with a decrease in temperature. Hence, even though fish with low acclimation capacity had greater maximal performance, high acclimation capacity may be advantageous when ecologically relevant behaviour requires submaximal locomotor performance. Trade-offs, developmental effects and the advantages of plastic phenotypes together are likely to explain the observed population variation.
Highlights
Temperature is one of the most relevant physical state variables in biology because physiological rates and fitness are influenced by the thermal environment (Tattersall et al, 2012)
In a bet-hedging scenario, populations comprise individuals with high capacity for acclimation that can fully compensate for an environmental change given sufficient time to acclimate and individuals with low acclimation capacity that cannot compensate physiological rates at all. We found this to be the case in mosquitofish (Gambusia holbrooki; Seebacher et al, 2015; Loughland and Seebacher, 2020)
We modelled different phenotypic compositions of populations by selecting subpopulations from the complete data set, which were the top 10% of fish with the highest acclimation capacity, the bottom 10% with the lowest acclimation capacity and the central 10%; each of these subpopulations was comprised of 61 fish
Summary
Temperature is one of the most relevant physical state variables in biology because physiological rates and fitness are influenced by the thermal environment (Tattersall et al, 2012). Variation in the thermal environment can be a strong predictor of individual fitness and population persistence (Kingsolver and Buckley, 2017). At a reductionist level, living organisms are comprised of networks of interacting biochemical pathways (Costanzo et al, 2021). The thermal sensitivity of higher organismal traits such as locomotor performance or metabolic rate is determined by the thermodynamics of flux through underlying biochemical pathways. Each physiological rate has a characteristic temperature response, which is captured by ‘thermal performance curves’ (TPC; Huey and Kingsolver, 1989)
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