Intraspecific variation in thermal tolerance and heat shock protein gene expression in common killifish,Fundulus heteroclitus

Abstract

SUMMARY Populations of common killifish, Fundulus heteroclitus, are distributed along the Atlantic coast of North America through a steep latitudinal thermal gradient. We examined intraspecific variation in whole-animal thermal tolerance and its relationship to the heat shock response in killifish from the northern and southern extremes of the species range. Critical thermal maxima were significantly higher in southern than in northern fish by ∼1.5°C at a wide range of acclimation temperatures (from 2-34°C), and critical thermal minima differed by ∼1.5°C at acclimation temperatures above 22°C, converging on the freezing point of brackish water at lower acclimation temperatures. To determine whether these differences in whole-organism thermal tolerance were reflected in differences in either the sequence or regulation of the heat shock protein genes(hsps) we obtained complete cDNA sequences for hsc70, hsp70-1 and hsp70-2, and partial sequences of hsp90α and hsp90β. There were no fixed differences in amino acid sequence between populations in either hsp70-1 or hsp70-2, and only a single conservative substitution between populations in hsc70. By contrast, there were significant differences between populations in the expression of many, but not all, of these genes. Both northern and southern killifish significantly increased hsp70-2 levels above control values(Ton) at a heat shock temperature of 33°C, but the magnitude of this induction was greater in northern fish, suggesting that northern fish may be more susceptible to thermal damage than are southern fish. In contrast, hsp70-1 mRNA levels increased gradually and to the same extent in response to heat shock in both populations. Hsc70 mRNA levels were significantly elevated by heat shock in southern fish, but not in northern fish. Similarly, the more thermotolerant southern killifish had a Ton for hsp90α of 30°C, 2°C lower than that of northern fish. This observation combined with the ability of southern killifish to upregulate hsc70 in response to heat shock suggests a possible role for these hsps in whole-organism differences in thermal tolerance. These data highlight the importance of considering the complexity of the heat shock response across multiple isoforms when attempting to make linkages to whole-organism traits such as thermal tolerance.

Triggers of the HSP70 stress response: environmental responses and laboratory manipulation in an Antarctic marine invertebrate (Nacella concinna)

“…Gracey et al 2008); however, the constitutive HSC70 has been designated the main heat-dependant HSP70 family member in the Pacific white shrimp (Litopenaeus vannamei; Wu et al 2008). This latter example may be species specific as there is increasing evidence that although HSC70 may upregulated by acute heat stress, it is often more likely to correlate with longer-term chronic stress such as that described here, in fluctuating temperature regimes (Podrabsky and Somero 2004;Todgham et al 2006) and under environmentally diverse bio-geographical distributions (Fangue et al 2006;Place et al 2008). The great flexibility of the HSP70 gene complex means that if it is to be used as an environmental biomarker, clearly as many family members as possible should be surveyed under a number of different conditions over both acute and chronic timescales.…”

“…Relative expression levels of HSP70 gene family members can vary according to bio-geographical location and demonstrate a plasticity of gene regulation within populations of the same species (Fangue et al 2006;Place et al 2008). Much of the research on the interaction between HSP70 genes and environmental stress involves non-model organisms and frequently uses gene fragments as assays (cf.…”

“…Much of the research on the interaction between HSP70 genes and environmental stress involves non-model organisms and frequently uses gene fragments as assays (cf. Fangue et al 2006). Without full genome information, it is impossible to categorically identify all members of a gene family and novel species-specific variants may always be discovered (cf.…”

Thermal acclimation and subspecies-specific effects on heart and brain mitochondrial performance in a eurythermal teleost (Fundulus heteroclitus)

“…Their ability to survive [critical thermal (CT) limits=−1 to 41°C] and acclimate (acclimation limits=2 to 35°C) over a large thermal range may be due to a thermally robust mitochondrial physiology (Fangue et al, 2009;Chung and Schulte, 2015) and acclimation capacity (Chung and Schulte, 2015;Fangue et al, 2009;Baris et al, 2016a). In addition, northern and southern subspecies of F. heteroclitus have undergone local adaptation to their thermal environments and have diverged for a number of traits such as whole-animal metabolic rates and thermal tolerance (Schulte, 2001;Fangue et al, 2006Fangue et al, , 2009. Despite the existence of genetic polymorphisms in genes encoding mitochondrial proteins that differentiate northern and southern killifish (Whitehead, 2009;Mckenzie et al, 2016), few clear differences in mitochondrial function exist between these subspecies (Baris et al, 2016a;Fangue et al, 2009), although differentiation in mitochondrial function has been examined in only heart (Baris et al, 2016a) and liver (Fangue et al, 2009), and nothing is known about the function of brain mitochondria in this species.…”

Genomics of Adaptation to Multiple Concurrent Stresses: Insights from Comparative Transcriptomics of a Cichlid Fish from One of Earth’s Most Extreme Environments, the Hypersaline Soda Lake Magadi in Kenya, East Africa

“…These included genes related to hyper-and hypo-osmotic stress (Kalujnaia et al 2007;Evans and Somero 2008;Laverty and Skadhauge 2012), heat stress (Fangue et al 2006;Purohit et al 2014), hypoxia and oxidative stress (Almeida et al 2002;Woo et al 2013) (see Table S1 for the complete list of genes). Additionally, we investigated the expression levels of the entire set of genes of the ornithine-urea cycle (OUC) pathway: N-acetylglutamate synthase (NAGS), ornithine carbamoyl transferase (OTC), carbamoyl-phosphate synthase III (CPSIII), argininosuccinate synthase (ASS), argininosuccinate lysase (ASL), and arginase (ARG), and one accessory urea pathway gene (ornithine glutamine synthetase (GS)) ( Table 2).…”