Phylogeny of Northern Hemisphere freshwater crayfishes based on 16S rRNA gene analysis

Freshwater crayfishes are divided into two superfamilies, and one of which exists only in the Southern Hemisphere (Parastacoidea), while another has been found only in parts of the Northern Hemisphere (Astacoidea). Although several conflict opinions have been revealed, monophyly of freshwater crayfishes, including the monophyly of crayfish superfamilies, are commonly accepted. The phylogenetic relationships among crayfish subgroups of the Northern Hemisphere, however, are rather controversial due to the disjunct zoogeographic distributions of two families, Astacidae and Cambaridae, and the enigmatic morphological affinities of eastern Asian crayfish genus Cambaroides to two families. In our 16S rDNA analysis, Cambaroides occupied the basal position of Astacoidea as a third group, and showed sister group relationships with the Cambaridae and Astacidae clades. Our results conflict with traditional taxonomy because the Cambaroides genus has been widely accepted as a member of the Cambaridae. However, they are in good agreement with recent molecular studies of crayfishes, and to a large degree with recent explanations of floristic exchanges among holarctic plant groups without enigmatic disjunction. Because many questions remain to be answered, it is desirable to note that, to obtain a reliable phylogeny of Northern Hemisphere crayfishes, more evidence must be collected from fossil records, biogeography of other freshwater animal groups, and multiple molecular data from both nuclear and mitochondrial genes.