The factors that permit or, at the least, are correlated with rapid speciation of a lineage when a founding member moves into a new habitat are little understood. Yet the phenomenon of adaptive radiation is considered significant, and numerous cases have been proposed over the years. One basic issue at the start needs to be established solidly, that is the phylogenetic relationships among the species of the radiating assemblage. A test case of precisely this matter is under investigation with North American crayfish of the genus Orconectes. Approximately 24 species of the subgenus Procericambarus inhabit a variety of streams, pools, and river margins at high and low elevations in middle North America, and provide opportunities to study the pattern of adaptive speciation into new ecological habitats. Faculty sponsor Alan Templeton and graduate student Keith Crandall are emphasizing molecular data from mitochondrial and nuclear DNA to establish a phylogeny of this group of animals. Special attention is being given to issues of assessing the statistical significance of these molecule-based phylogenetic reconstructions, and such statistical tests are likely to have general applicability to studies by other researchers. With a robust phylogenetic estimate in hand, the investigators can then explore such questions as: are habitat divergence and geographic isolation among species independently associated through evolutionary time or do they interact with speciation events? Does a transition into a very different habitat type lead to much subsequent speciation (the well-known adaptive zone hypothesis of the late paleontologist G. G. Simpson)? Can speciation occur within an isolated drainage only if it is associated with habitat divergence? As well, the investigators will study aspects of morphological change including overall size reduction in these crayfish against the background of their molecularly based phylogeny.
