Limited variability in upper thermal tolerance among pure and hybrid populations of a cold-water fish.

Zachery R R Wells,Lauren J Chapman,Dylan J Fraser,Laura H Mcdonnell

doi:10.1093/conphys/cow063

Zachery R R Wells, Lauren J Chapman + Show 2 more

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https://doi.org/10.1093/conphys/cow063

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Abstract

As climate warming threatens the persistence of many species and populations, it is important to forecast their responses to warming thermal regimes. Climate warming often traps populations in smaller habitat fragments, not only changing biotic parameters, but potentially decreasing adaptive potential by decreasing genetic variability. We examined the ability of six genetically distinct and different-sized populations of a cold-water fish (brook trout, Salvelinus fontinalis) to tolerate acute thermal warming and whether this tolerance could be altered by hybridizing populations. Critical thermal maximum (CTmax) assays were conducted on juveniles from each population to assess thermal tolerance, and the agitation temperature was recorded for assessing behavioural changes to elevated temperatures. An additional metric, which we have called the 'CTmax-agitation window' (CTmax minus agitation temperature), was also assessed. The CTmax differed between five out of 15 population pairs, although the maximal CTmax difference was only 0.68°C (29.11-29.79°C). Hybridization between one large population and two small populations yielded no obvious heterosis in mean CTmax, and no differences in agitation temperature or CTmax-agitation window were detected among pure populations or hybrids. Summer variation in temperature within each stream was negatively correlated with mean CTmax and mean CTmax-agitation window, although the maximal difference was small. Despite being one of the most phenotypically divergent and plastic north temperate freshwater fishes, our results suggest that limited variability exists in CTmax among populations of brook trout, regardless of their population size, standing genetic variation and differing natural thermal regimes (temperature variation, minimum and maximum). This study highlights the level to which thermal tolerance is conserved between isolated populations of a vertebrate species, in the face of climate warming.

Highlights

Human-induced climate change may be the single greatest threat to global biodiversity (Sala et al, 2000)
From 13 to 26 October 2014, gametes were collected from six Cape Race (CR) populations: Cripple Cove (CC), Freshwater (FW), Ouananiche Beck (OB), Still There By Chance (STBC), Whale Cove (WC) and Watern Cove (WN)
Mean agitation temperature and critical thermal maximum (CTmax)–agitation window did not differ between all other pure populations, and the variance of all traits did not differ between pure populations (Fig. 2)

Summary

Introduction

Human-induced climate change may be the single greatest threat to global biodiversity (Sala et al, 2000). Climate change can interact with habitat fragmentation by creating physical (i.e. drought) or physiological (i.e. temperature) barriers (Hughes, 2000; Walther et al, 2002; Pearson and Dawson, 2003; Travis 2003), which limit the potential for independently. Too do the populations within them, resulting in a loss of genetic diversity via an increased likelihood of inbreeding, genetic drift and reduced gene flow (Young et al, 1996; Keller and Largiader, 2003; Andersen et al, 2004; Ezard and Travis, 2006) This process reduces adaptive potential, the ability of a population to tolerate environmental change, and further decreases population size. When studying population responses to climate warming, it is important to consider both the relative benefits of population size and hybridization concurrently

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