Conservation genetic assessment of the paleback darter (Etheostoma pallididorsum), a narrowly distributed endemic in the Ouachita Highlands, Arkansas, USA

The Paleback Darter is considered imperiled and has recently been
petitioned for listing under the Endangered Species Act. Prior
allozyme-based studies found evidence of small effective population size,
warranting conservation concern. The objective of this study was to assess
population dynamics and the phylogeographic history of the Paleback
Darter, using a multilocus microsatellite approach and mitochondrial DNA.
The predictions of this study were that Paleback Darter populations will
exhibit low genetic diversity and minimal gene flow; population structure
will correspond to river systems where samples are derived; the reservoir
dams impounding the reaches between the Caddo and Ouachita rivers would
serve as effective barriers to gene flow; and the Caddo and Ouachita
rivers are reciprocally monophyletic. Microsatellite DNA loci revealed
significant structure among sampled localities (global Fst = 0.17, P
< 0.001), with evidence of two distinct populations representing
the Caddo and Ouachita rivers. However, Bayesian phylogeographic analyses
resulted in three distinct clades, Caddo River, Ouachita River, and Mazarn
Creek. Divergence from the most recent ancestor shared among the river
drainages was estimated at 60-KYA. Population genetic diversity was
relatively low (He = 0.65; mean alleles per locus [A] = 6.26), but
comparable to close relatives, Slackwater Darter (He = 0.65; A = 6.74) and
Tuscumbia Darter (He = 0.57; A = 5.53). These results have conservation
implications for Paleback Darter populations and can be informative for
other headwater specialist species. Like other headwater species with
population structuring and relatively low genetic diversity, persistence
of Paleback Darter populations is likely tied to persistence and
connectivity of local breeding and non-breeding habitat. These results do
not raise conservation concern for a population decline; however, the
restricted distribution and endemic status of the species still renders
Paleback Darter populations vulnerable to extirpation or extinction.