Phylogeny of the freshwater crayfish subfamily Cambarinae based on 16S rDNA gene analysis

Freshwater crayfish have been a mainstay in biological experiments as a model species ever since Huxley’s seminal publication The Crayfish. Crayfish have been used in research ranging from vision pigment studies to neural physiology. Non-native species have been introduced on four continents due to their immense economic value. Although crayfish taxonomy is reasonably well resolved at the highest levels, there are many problems at the levels of genus and species. New exploration, technology and methodology have led to the discovery of not only new species but to a phylogenetic complexity that would not have been imagined in Huxley’s era. This complexity is caused by the conservatism of some morphological characters, high intraspecific diversity and convergence. The ambiguity of crayfish taxonomy is particularly evident for species native to South Georgia and North Florida, which are centers of crayfish diversity. Molecular phylogenetic analyses were employed to provide insight into three aspects of crayfish phylogeny. Using partial data from the 16S ribosomal gene, we determined: (a) the evolutionary relationships of a previously unanalyzed species, Procambarus spiculifer, (b) relationships within the genus Procambarus, and (c) the phylogeny of the entire subfamily Cambarinae. The resulting maximum likelihood tree produced phylogenies that were significantly different from the traditional systematic representation of relationships within the subfamily. Specifically, we show that the subfamily Cambarinae should not be divided into three distinct clades according to the genera Procambarus, Cambarus, and Orconectes. While most members of the genus Procambarus cluster within a single monophyletic clade, the genus Orconectes comprises a parayphyletic grouping that appears to also include members of the genus Cambarus.