9303258 CRANDALL Within the North American crayfish fauna there are at least 13 proposed independent species colonizations of the cave environment; the evolutionary divergences span nearly 60 million years. These troglobitic species exhibit loss of vision, lack of pigment, and other aptations to the subterranean environment. Such characters in this taxon make it possible to test hypotheses about effects of vision loss at the molecular level. Thirteen species pairs, consisting of one troglobitic (blind) and one epigean (not blind) species, will be compared for molecular level changes in the gene for the visual pigment rhodopsin. Effects of relaxed functional constraint on the molecular evolution of the rhodopsin gene, in terms of nucleotide substitutions, amino acid substitutions, and functional domains, will be examined. This comparative approach will benefit from substantial statistical power not previously available in studies of relaxed functional constraint. In addition the utility of the rhodopsin gene in phylogenetic analyses is to be explored, along with investigation of relationships of the ten genera of the crayfish subfamily Cambarinae. %%% In this study that will generate comparative data on the molecular evolution of DNA sequences both with and without functional constraint, higher rates of genetic codon substitution are predicted in the case of evolution without functional constraints (troglobitic species). Under cond ition of functional release, equal rates of substitution are expected at each nucleotide position within a codon. These mutational events will be interpreted in a context of tertiary (3 dimensional) structure of the crystallized protein of rhodopsin, which is comprised of 15 definable domains. Mutational "hotspots" can then be detected and interpreted in terms of genetic function. Perhaps the most potent general effect of this research will be to demonstrate the interpretive advantage which can be derived by adopting the phylogenetic approach when attacking biological questions at the molecular genetic level. ***
