BIOCHEMICAL SYSTEMATICS AND EVOLUTION OF THE CRAYFISH GENUS ORCONECTES (DECAPODA, CAMBARIDAE)

Phylogenetic relationships among 30 species of the North American cray fish genus Orconectes were investigated by examining 56 presumptive en zyme-coding loci using the technique of horizontal starch gel electrop horesis. Specimens were obtained from each of the 10 recognized subgen era and represent 14 of the 15 species-groups. Specimens from 2 additi onal genera (2 species of Cambarus and 3 species of Procambarus) were also included as outgroups. The most striking result in this investiga tion is the clustering of the troglobitic species of the subgenus O. ( Orconectes) in a group by themselves. The allozyme data indicate that these cave species are very divergent (Nei's D greater than or equal t o 0.3577) from other members of the genus and appear more closely rela ted to the outgroup species of Cambarus (mean D = 0.3522). This result suggests that O. (Orconectes) is a monophyletic lineage that deserves generic recognition, as previously proposed by Creaser (1962). In add ition, no monophyletic lineages were found that support the other subg enera or ally their species groups, a result consistent with recent DN A sequence data. However, a bootstrap analysis of these data suggests that the allozyme phylogeny is poorly resolved among the other subgene ra of Orconectes. This indicates, perhaps, that the limits of the allo zyme technique to distinguish phylogenetic relationships at the subgen eric level were reached (i.e., insufficient levels of variation were d etected). The distribution of alleles at some loci, however, might pro vide insight into the evolutionary history and past dispersal patterns of these crayfish species. These data lend support to the thesis of F itzpatrick (1987) that some ancestral orconectid stocks established th emselves west of the Mississippi River where they eventually diverged from the stocks found to the east on the Cumberland Plateau. Unique al leles found only in species of the Ozark Highlands suggest also that t his area played a pivotal role in the evolution and diversification of ancestral crayfish stocks.