Rand 9801563 Previous work has shown that natural selection is important in determining the distribution of two different genetic variants of a key enzyme responsible for carbohydrate metabolism in the intertidal acorn barnacle, Semibalanus balanoides. Barnacles with one enzyme variant of mannose phosphate isomerase (Mpi) exhibit higher survivorship in hotter, high-intertidal sites, while barnacles with the other Mpi variant have higher survivorship at more benign sites such as the low intertidal and under seaweeds. The proposed experiments will examine the survivorship of barnacles with different enzyme variants under controlled conditions in a flowing sea water tank. Temperature, desiccation, and the availability of mannose will be manipulated in a factorial design. Barnacles that have settled onto rock slabs in the wild will be brought into the lab and allowed to grow under different combinations of conditions. The proportions of Mpi enzyme variants before and after experimental treatments will provide explicit information about the action of natural selection on this enzyme that regulates a key step in the conversion of dietary mannose (from marine algae) into cellular energy. The research will bear on the role of heterogeneous environments in the maintenance of genetic variation in natural populations.
