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First published online July 20, 2006
Journal of Experimental Biology 209, 2859-2872 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02260

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

Nann A. Fangue^1,*, Myriam Hofmeister^1,2 and Patricia M. Schulte¹

¹ Department of Zoology, University of British Columbia, 6270 University Blvd., Vancouver, BC V6T 1Z4, Canada
² Department of Biology, Universität Konstanz, Konstanz, Germany

View larger version (18K): [in a new window]   Fig. 1. Chronic thermal maxima for northern (NH, triangles) and southern (GA, circles) killifish. Chronic thermal minima (data not shown) were estimated to be -1.1°C for both populations. Data were fit with a third order regression for calculations of maxima and minima.

View larger version (25K): [in a new window]   Fig. 2. Critical thermal maxima (CTMax; A) and minima (CTMin; B) for northern (NH, triangles) and southern (GA, circles) killifish acclimated to temperatures between 2.3°C and 34.0°C and a 12 h:12 h L:D photoperiod. Second order regression models of CTMax or CTMin within a population are shown. Significant differences in CTMax or CTMin within a population are indicated by different letters. An asterisk indicates a significant difference in critical thermal limit between populations at a given acclimation temperature. Values are mean ± s.d. (N=12-15, as indicated in Table 3); P<0.001 for all significant comparisons.

View larger version (28K): [in a new window]   Fig. 3. Critical thermal maxima (CTMax; A) and minima (CTMin; B) for three northern [Nova Scotia (NS), Maine (ME) and New Hampshire (NH); hatched] and three southern [Georgia (GA), Fernandina Beach, FL (FB) and Whitney Island, FL (WI); grey] populations of killifish acclimated to 22°C and 12 h:12 h L:D photoperiod. Values are mean ± s.d., N=15; significant differences between populations within each panel are indicated by different letters (P<0.001 for all significant comparisons).

View larger version (36K): [in a new window]   Fig. 4. Phylogenetic relationships among vertebrate hsc/hsp70 amino acid sequences. The tree was constructed using the neighbor-joining method and bootstrap values (percentage of 1000 replicates) are shown at each branch point. Bold font indicates the sequences identified in this study. GenBank accession numbers of all sequences are given in brackets following the gene name.

View larger version (29K): [in a new window]   Fig. 5. Branchial hsc70 (A), hsp70-1 (B) and hsp70-2 (C) mRNA levels in northern (NH, hatched bars) and southern (GA, grey bars) killifish in response to heat shock. Control (C) samples were taken prior to experimentation, and handling controls (CH) were treated the same as the experimental temperature groups but were transferred back to the acclimation temperature of 20°C. All mRNA data is normalized to the control gene EF-1 (values are mean ± s.e.m.; N=6). Different letters indicate significant differences between treatments but within a population, and an asterisk indicates a significant difference between northern and southern fish within a treatment.

View larger version (43K): [in a new window]   Fig. 6. Branchial hsp90 (A) and hsp90ß (B) mRNA levels for northern (NH, hatched bars) and southern (GA, grey bars) killifish exposed to heat shock. Control (C) samples were taken prior to experimentation, and handling controls (CH) were treated identically to the heat shock groups but exposed only to the acclimation temperature of 20°C. All mRNA expression data is normalized to the control gene EF-1 (values are mean ± s.e.m.; N=6). Different letters indicates significant differences between treatments but within a population, and an asterisk indicates a significant difference between northern and southern fish within a treatment.