Physiological Determinants of Vertical Zonation in Congeneric Marine Invertebrates: Comparative Analysis of Species Replacement Along the Subtidal to Intertidal Gradient

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A question of great interest to ecologists and evolutionary biologists is, "Why do species occur in certain habitats and not in others?" One basis for governing the distributions of species is their tolerance of physical factors in the environment, notably ambient temperature. This fact is illustrated especially clearly in rocky intertidal habitats: In the gradient from the subtidal region to the intertidal zone, thermal conditions vary sharply, as does the set of species found along this transect. It is common for one species of a genus to be replaced by a closely related species of the same genus (a congener). The studies supported by this proposal examine the physiological, biochemical and molecular differences among congeners from different vertical sites in an effort to identify adaptive differences that help to explain variation in distribution patterns. The systems to be studied include: (i) the heat-shock response, a rescue system for repairing heat-damaged proteins; (ii) heart function, which is markedly sensitive to temperature; (iii) membrane integrity, which is essential for many physiological processes, and (iv) nerve function, which may be of importance in setting thermal tolerance limits. Techniques to be used include a wide variety of molecular methods (sequencing of genes and analysis of gene expression patterns), biochemical approaches (measurement of levels of heat-damaged proteins) and physiological analyses (rates of heart function and generation of nerve signals). Study species include snails of the genus Tegula and porcelain crabs (genus Petrolisthes). Both sets of congeners occur over wide vertical and latitudinal ranges and thus are excellent study systems for elucidating mechanisms of adaptation to temperature. The study of congeners adapted to different temperatures allows a particularly clear picture to be developed of the role of adaptive change in establishing environmental optima and tolerance limits. By identifying the underlying mechanisms that establish thermal optima and limits, the effects of predicted global warming could be understood in a more definitive manner.