Cryptic diversity within two endemic crayfish species of the Southeastern US revealed by molecular genetics and geometric morphometrics

Crayfishes reach their peak biodiversity in North America, with the Mobile Basin of the southeastern US harboring high levels of endemism. However, the genetic diversity and phylogeography of crayfishes from this region are poorly understood. Here, the genetic structure and shape variation among multiple populations of Cambarus englishi Hobbs and Halland Cambarus halli Hobbs, both endemic to the Tallapoosa River, were examined from three catchments of the drainage (Upper, Little, and Middle) using mitochondrial cytochrome c oxidase subunit I (COI) gene sequences and geometric morphometrics. Notably, a combined COI network analysis found haplotypes from each species coalescing into common networks based on catchment, with significant genetic differentiation being identified between nearly all populations. Geometric morphometric analyses largely agreed with genetic analyses, with shape overlap yet significant differences between species and between the three catchments for C. halli (but not C. englishi). Together this suggests that genetic separation is manifested in part by shape variation and overall, these crayfishes appear to represent "cryptic species complexes." Our data provide evidence for the establishment of evolutionarily significant units along the Upper, Little, and Middle Tallapoosa and that there is considerable population isolation and cryptic diversity within North American crayfishes.