Mechanisms of environmental adaptation in fish

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Temperature affects biological processes at all levels of organization from individual molecules, to individual organisms, to whole ecosystems. Temperature is thus critical factor influencing the distribution and abundance of all species, and particularly of ectotherms such as fish. Despite several decades of study, however, we still do not have a complete understanding of how fish respond to changes in environmental temperature during their lifetimes, or how adaptation to environmental temperature occurs over evolutionary time. Here we propose to use two species of small fish (killifish and stickleback) as models to address these questions. We have previously shown that there is variation among populations within each species in a variety of characteristics related to thermal biology, such as the temperatures they can tolerate. Northern populations of killifish also have higher resting metabolic rate than do southern populations, which may be an adaptation to the low temperatures and short growing seasons of northern latitudes. In addition, northern populations of killifish are able to increase the amount of mitochondria (an energy producing structure) in their cells in response to cold temperatures, while killifish from southern populations cannot mount this compensatory response. Here we propose to use cutting edge genomic methods combined with detailed biochemical and physiological analyses to understand the mechanisms that cause this intraspecific variation in thermal biology. Specifically, we will test the hypothesis that variation in mitochondrial properties is related to variation in resting metabolic rate, and ask whether any other processes also contribute to this variation. We will then examine the mechanisms responsible for variation in the amounts of mitochondria in response to low temperature, and the mechanisms that cause differences in temperature tolerance. Together this research will provide novel insights into the genetic, physiological and molecular mechanisms underlying responses to temperature changes on both short and long time scales. Understanding these mechanisms is particularly relevant today given the likely effects of global climate change.