Jw. Fetzner, BIOCHEMICAL SYSTEMATICS AND EVOLUTION OF THE CRAYFISH GENUS ORCONECTES (DECAPODA, CAMBARIDAE), Journal of crustacean biology, 16(1), 1996, pp. 111-141
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.