1. 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.
2. 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.
3. Microsatellite DNA loci revealed significant structure among sampled localities (global F_st = 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 (H_e = 0.65; mean alleles per locus [A] = 6.26), but comparable to close relatives, Slackwater Darter (H_e = 0.65; A = 6.74) and Tuscumbia Darter (H_e = 0.57; A = 5.53).
4. 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.

Tissue samples were collected from up to 30 Paleback Darter individuals per locality throughout the Ouachita River basin in southwestern Arkansas. A total of 181 individuals were successfully genotyped for 8 microsatellite DNA loci, with primers designed for the Greenside, Candy, Rainbow, Cherokee, and Orangethroat darters. Up to 10 individuals per sub-drainage were additionally amplified for the mitochondrial cytochrome b gene (cyt b). The cyt b sequences were accessioned with GenBank.

Microsatellite data GENEPOP format

PalebackDarter_Genepop.txt

The microsatellite DNA data file is in GENEPOP format. The file includes genotype scores for 8 microsatellite loci for the Paleback Darter. Locus names are listed under the title line at the top of the file. POP refers to populations described in the manuscript. The populations are ordered as follows: (1) Caddo River; (2) tributary to the Caddo River, Polk Creek; (3) tributary to the Caddo River, Lick Creek; (4) tributary to the Ouachita River, Big Fork Creek; (5) tributary to the Ouachita River, Kate's Creek; (6) tributary to the Ouachita River, Big Hill Creek; (7) tributary to the Caddo River, Collier Creek; (8) tributary to the Ouachita River, Mazarn Creek. Each row below POP identifiers represents an individual followed by their genotype for the 8 loci. Individual identifiers and specimen information can be found in the associated excel file named "PalebackSpecimenInfo.xlsx". Allele scores for each locus are concatenated into six digits, with the first three numbers representing the size of allele one and the second three numbers representing the size of allele two. Missing data are coded as "000".

Specimen Information

PalebackSpecimenInfo.xlsx

Detailed information for Paleback Darter samples used in this study. Museum tissue catalog or specimen voucher catalog numbers are followed by individual identifiers and collection locality information. Specimens and/or tissues were cataloged in the Arkansas State University Museum of Zoology (ASUMZ) in the Arkansas Center for Biodiversity Collections.