Somero 9700701 Marine porcelain crabs of the genus Petrolisthes occur over a wide geographical range--from extremely hot tropical environments to cold north- and south temperate regions--and at widely different heights in the intertidal and subtidal zones. Thus, congeners of Petrolisthes encounter substantial differences in mean temperature and temperature range, making these crabs an excellent study system for examining evolutionary adaptation to temperature within a relatively narrow taxonomic group. The PI's initial studies of two congeners, P. eriomerus and P. cinctipes from low- and high intertidal zones, respectively, indicate pervasive adaptations to temperature and emersion stress. The proposed studies build on this work, and include, for several additional congeners: (1) determination of upper lethal temperature limits; (2) examination of the temperature sensitivity of structural and kinetic properties of lactate dehydrogenase; (3) determination of the function of leg membrane structures in gas exchange; and (4) development of a molecular phylogeny, using the sequence of the large subunit ribosomal RNA gene The latter experiments will enable analysis of the interspecific differences in physiological-biochemical-molecular traits to be analyzed in a phylogenetic context, thus enabling putative "adaptive" differences to be distinguished from changes not due to evolutionary responses to temperatures. .
