Genetic variation within and among crayfish species

The amount of genetic variation within and among species is an important index for many astacological studies, including; conservation biology, aquaculture, systematics, and population genetics. Our current knowledge of the existing levels of variation in crayfish species is scant. Crayfish species are reputed to have exceptionally low levels of variation both within and among species. This inference has been made from early protein electrophoretic studies. In this paper, I examine the extent to which this inference holds, given a larger database of protein studies. I then explore the levels of genetic variation at the nucleotide sequence level for various taxonomic hierarchical levels, including; within species, among species within a genus, among genera within a family, and among families. I examine nucleotide sequence variation from both mitochondrial (16S ribosomal) and nuclear gene regions (rhodopsin and ITS2). Finally, a list of gene regions with known crayfish sequences is offered for future studies of genetic variation in crayfishes.