POWRE: A New Method to Test Hypotheses about the Development and Evolution of Endothermy in Tunas: Pilot study

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This POWRE project will provide the resources needed for the PI to adapt a technique to measure proton "leak" across the inner mitochondrial membrane as a measure of tissue heat production to her established study system of the development and evolution of endothermy in tunas. During the summer of 1999 (prior to the start of POWRE funding), the PI will learn the technique in the lab of Dr. Martin Brand (funded by an NIH grant). The POWRE grant will enable the PI to establish the technique at the home institution and to conduct pilot studies there on several fish species, with undergraduate student collaborators, to test the hypothesis that endothermic fishes have an elevated rate of proton leak across the inner mitochondrial membrane of the thermogenic tissue (red muscle). These tests will involve comparisons of tunas with their ectothermic sister taxa (chub mackerel and eastern Pacific bonito), and of the mako shark with ectothermic sharks. If the hypothesis is supported, the resultant elevation in tissue heat-production rate would correspond to the elevated standard or "maintenance" metabolic rates of tunas (and presumably in makos). Future studies will test two hypotheses: (1) that the change in mitochondrial proton leak was an important step in the evolution of endothermy; this will involve phylogenetically based comparisons of a number of species and additional ectothermic sister taxa. (2) As juvenile tunas develop the capacity to maintain elevated temperatures in their slow-twitch, oxidative locomotor muscle (red myotomal muscle) across the size range of 100-300 mm fork length (FL), the heat production rate of this tissue is increased by increasing the rate of proton leak across the inner mitochondrial membrane. POWRE funding will allow the PI to explore a new research approach and apply it to advance the field by more directly testing for unique features of the thermogenic tissue in tunas and the mako shark.