The Caddo Madtom, Noturus taylori, is endemic to three river drainages of the Ouachita Highlands in the southeastern United States. Conservation concern for N. taylori has been heightened by recent studies based on analyses of allozyme data suggesting population decline and a possible extirpation event, which lead to N. taylori petitioned for listing under the Endangered Species Act in 2011. The objective of this study was to determine if contemporary factors, historic processes, or a combination of both, using microsatellite DNA loci and mitochondrial (mt) DNA, have influenced patterns of genetic structuring for N. taylori to better inform conservation management strategies. Phylogeographic and Bayesian cluster analyses suggest that genetic structuring between Caddo and Ouachita river drainages was shaped by historical processes prior to construction of reservoir dams that dissect the drainages. We found no evidence that reservoir dams influenced contemporary patterns of genetic structure, thus it is likely that larger river courses, and life-history characteristics conducive to headwater habitats, play important roles in limiting gene flow between drainages, and to some extent within drainages. Genetic diversity of N. taylori was relatively high compared to other endangered madtom species; however, compared to the Ouachita River population, genetic diversity was significantly lower for the Caddo River population. Collectively, these results suggest that N. taylori populations are not heavily impaired, and the genetic variation and structuring is most attributable to historic processes. However, the endemic status and narrowly fragmented distribution still renders N. taylori populations vulnerable to extirpation or extinction by stochastic events.

Tissues samples were collected from up to 30 Caddo Madtom individuals per locality throughout the Ouachita River basin in southwestern Arkansas. A total of 137 individuals were successfully genotyped for 10 microsatellite DNA loci, with primers designed for the Slender, Smoky, and Yellowfin madtoms. 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

The microsatellite DNA data file is in GENEPOP format. The file includes genotype scores for 10 microsatellite loci for the Caddo Madtom. 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, Lick Creek; (3) South Fork Caddo River; (4) Ouachita River; (5) South Fork Ouachita River. Each row below POP identifiers represents an individual followed by their genotype for the ten loci. Individual identifiers and specimen information can be found in the associated excel file named "SpecimenInformation_Dryad.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".

CaddoMadtom_GENEPOP.txt

SpecimenInformation_Dryad

Detailed information for Caddom Madtom 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).