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

Abstract

Phylogenetic relationships among 30 species of the North American crayfish genus Orconectes were investigated by examining 56 presumptive enzyme-coding loci using the technique of horizontal starch gel electrophoresis. Specimens were obtained from each of the 10 recognized subgenera and represent 14 of the 15 species-groups. Specimens from 2 additional genera (2 species of Cambarus and 3 species of Procambarus) were also included as outgroups. The most striking result in this investigation is the clustering of the troglobitic species of the sub-genus O. (Orconectes) in a group by themselves. The allozyme data indicate that these cave species are very divergent (Nei's D ≥ 0.3577) from other members of the genus and appear more closely related 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 addition, no monophyletic lineages were found that support the other subgenera or ally their species groups, a result consistent with recent DNA sequence data. However, a bootstrap analysis of these data suggests that the allozyme phylogeny is poorly resolved among the other subgenera of Orconectes. This indicates, perhaps, that the limits of the allozyme technique to distinguish phylogenetic relationships at the subgeneric level were reached (i.e., insufficient levels of variation were detected). The distribution of alleles at some loci, however, might provide insight into the evolutionary history and past dispersal patterns of these crayfish species. These data lend support to the thesis of Fitzpatrick (1987) that some ancestral orconectid stocks established themselves west of the Mississippi River where they eventually diverged from the stocks found to the east on the Cumberland Plateau. Unique alleles found only in species of the Ozark Highlands suggest also that this area played a pivotal role in the evolution and diversification of ancestral crayfish stocks.