Differential plasticity of membrane fatty acids in northern and southern populations of the eastern newt (Notophthalmus viridescens)
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Seasonal changes in membrane composition and metabolic activity allow many temperate ectotherms to contend with changes in body temperature, but few studies have investigated whether the plasticity of these traits has diverged within a single species. Therefore, we studied the effects of thermal acclimation on the membrane fatty acid composition and the activities of cytochrome c oxidase (CCO) and citrate synthase (CS) in the skeletal muscle and liver of eastern newts from Maine and Florida. Newts were acclimated to either 6 °C or 28 °C for 12 weeks prior to experiments. Cold acclimation resulted in a lower saturated fatty acid (SFA) content in the muscle membranes of both populations. SFA content in liver was lower in cold compared to warm-acclimated newts from Florida, but acclimation did not affect SFA content in liver membranes of the Maine population. In liver, cold acclimation resulted in a higher monounsaturated fatty acid (MUFA) content in the Florida population and a higher polyunsaturated fatty acid (PUFA) content in the Maine population. Regardless of acclimation conditions, the muscle and liver membranes of the Maine population had higher SFA and PUFA contents compared to those of the Florida population. MUFA content of muscle and liver membranes was higher in the Florida population compared to the Maine population. The effect of acclimation on CCO and CS activity was tissue-specific. In muscle, CCO and CS activities were higher in cold compared to warm-acclimated newts in both populations, and CS and CCO activities were higher in the Maine compared to the Florida population. In liver, CCO and CS activity were unaffected by acclimation in the Florida population, but activity was lower in cold compared to warm-acclimated Maine newts. These results demonstrate that the phenotypic plasticity of these traits in response to seasonal change has diverged between northern and southern populations.
KeywordsAcclimation Adaptation Thermal Temperature Seasonal
We thank the Company of Biologists for providing a travel fellowship for Patrick Mineo to travel to Dr. Nancy J. Berner’s lab to measure membrane fatty acid composition for this project. We also thank Michael Oxendine for his assistance collecting newts and Keely Corder for her assistance with enzyme assays. Rick Wilson and Andrew McCullough from the Cathance River Preserve and Brunswick High School also deserve thanks for their assistance in locating and collecting newts in Maine. A. John Bailer, Jon P. Costanzo, Kathleen A. Killian, and Richard E. Lee, Jr. contributed constructive critiques of this manuscript. We also thank Rachael Morgan-Kiss for allowing use of her spectrophotometer. This work was supported by a Journal of Experimental Biology travel fellowship to PMM, the National Science Foundation [IOS:1120448 to NJB], and departmental funds to PJS and PMM.
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