Nucleotide Polymorphism in Heterogeneous Environments: Mpi in Semibalanus

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This research concerns the role of genetic variation at metabolic enzyme genes in the adaptation to heterogeneous environments. Recent work has shown that acorn barnacles (Semibalanus balanoides) carrying alternative forms of the enzyme encoded by the MPI gene experience different survivorship at opposite ends of the environmental gradient between high- and low-tide zones. Other genetic markers in the acorn barnacle genome do not show this pattern, thus implicating natural selection at or near the MPI gene. The investigators propose to clone the MPI gene, determine its DNA sequence, and identify the specific changes in MPI that confer the habitat-specific survivorship of the two enzyme forms. This will be achieved by DNA sequence analyses of the two forms of the MPI gene, by analyses of single nucleotide polymorphisms in the gene that vary between tide zones, and through growth and survivorship experiments in a flowing sea water lab where thermal stress and dietary sugars important in MPI function are manipulated. The goal of this research is to understand the functional significance of genetic variation in heterogeneous environments. All organisms face environmental unpredictability; how they respond to this uncertainty through genetic adaptations is a fundamental problem in the biological sciences. In barnacles, two crucial environmental variables are thermal and desiccation stress. Because these stresses will increase in the future, this barnacle model may help us understand the genetic impacts of climate change.