Phylogeography and conservation genetics of the hellbender salamander (Cryptobranchus alleganiensis)

Abstract

We investigated hellbender phylogeography through phylogenetic analyses of individuals sampled from 16 locations throughout their range in the eastern United States. Analyses were conducted on concatenated cytochrome-oxidase I (COI), cytochrome-b (Cytb) and NADH dehydrogenase subunit 4 (ND4) mtDNA sequence, totaling 2160 nucleotides. Hellbender haplotypes differed by 0.1 to 5.8% maximum likelihood (ML) corrected sequence divergence. Phylogenetic analyses reveal that hellbenders are separated into 8 reciprocally monophyletic populations or clades differentiated by a minimum of 0.7 to 5.4% sequence divergence, each of which constitutes a separate Management Unit (MU). High among population divergence and reciprocal monophyly suggest that femalemediated gene flow is severely restricted or non-existent among each MU. Hellbenders are currently divided into two subspecies, Cryptobranchus alleganiensis alleganiensis and C. a. bishopi based on morphological characters. The phylogenetic analyses presented here strongly indicate that these subspecies are paraphyletic. Management priorities for the hellbender should be reconsidered in light of these new molecular data. Results from Bayesian rooting indicate the root of the hellbender mtDNA tree lies on the branch leading to hellbender haplotypes from the Current, Eleven Point and New Rivers. The rooted tree suggests that a common ancestor in the southern Ozarks and/or southern Appalachians gave rise to northern hellbender populations, consistent with a Pleistocene refuge hypothesis.

Genetic relationships of hellbenders in the Ozark highlands of Missouri and conservation implications for the Ozark subspecies (Cryptobranchus alleganiensis bishopi)

“…For the north-flowing streams of C. a. alleganiensis, mitochondrial sequence divergence among drainages is low (\0.3%; Sabatino and Routman 2009). Our data indicate that there is fine scale population structure among eastern hellbender populations in the northern Ozark drainages, as demonstrated by the significant genetic distance between the Big Piney River and the Meramec and Niangua Rivers, but not between the Big Piney and Gasconade Rivers.…”

“…Studies of hellbenders using mitochondrial markers (Routman 1993;Routman et al 1994;Sabatino and Routman 2009) have detected phylogeographic patterns that can aid protection and restoration efforts. Our study has demonstrated that the patterns became clearer when nuclear variation was added to the conservation arsenal.…”

“…Sabatino and Routman (2009) concluded that female-mediated gene flow was limited because they found strong mtDNA differentiation among populations, but little within-population variation. Our microsatellite results revealed a similar pattern, suggesting that neither sex has long-distance dispersal.…”

“…Mitochondrial DNA differentiation is considerable between drainages but is relatively limited within-drainages (Routman 1993;Routman et al 1994). Phylogenetic analyses based on mitochondrial DNA revealed a paraphyletic relationship between the subspecies (Sabatino and Routman 2009). Our study objectives were to use genotypic information at multiple microsatellite loci to (1) quantify genetic diversity of Missouri populations of C. a. alleganiensis and C. a. bishopi, (2) reveal the extent of structure within basins and populations, and (3) delineate management units for conservation efforts that may involve propagation and release of the species.…”

Historic occurrence of the amphibian chytrid ­fungus Batrachochytrium dendrobatidis in ­hellbender Cryptobranchus alleganiensis ­populations from Missouri

“…The Ozark hellbender C. a. bishopi is endemic to south-flowing streams within the Black and White River drainages of southern Missouri and northern Arkansas. Currently, there are 7 relatively isolated, extant hellbender populations in Missouri that are identified by river (Routman et al 1994, Sabatino & Routman 2008. Eastern hellbender populations in Missouri include those from the Niangua, Big Piney, Gasconade, and Meramec Rivers, while the Current, Eleven Point, and North Fork of the White Rivers represent the range of the Ozark subspecies (Fig.…”