The Barrens Darter, Etheostoma forbesi, is one of the most geographically restricted freshwater fish species in North America, with a distribution limited to headwater portions of nine streams in the western part of the upper Caney Fork, a tributary of the Cumberland River in Tennessee. This limited geographic distribution makes E. forbesi especially vulnerable to potential threats posed by human alterations to rivers and streams, and the risk of ecological competition and introgressive hybridization with the closely related Fringed Darter, E. crossopterum. Museum collection records and targeted surveys conducted since its description suggest that E. forbesi’s present-day range does not include several streams it previously inhabited– some as recently as 15 years ago. We investigate the geographic distribution and variation in meristic traits of both E. forbesi and E. crossopterum in the upper Caney Fork system through the examination of all available museum vouchers, and assess phylogeographic patterns among populations using mitochondrial DNA sequence data. We report a newly discovered population of E. forbesi from the upper Collins River, and present evidence that E. crossopterumhas displaced E. forbesi in the Hickory Creek system and Mud Creek in the upper Barren Fork River system. Meristic differences between the species are slight, but and fin ray counts can provide a visual means of identifying species and potential hybrid individuals. Analysis of mtDNA variation indicates gene flow between E. forbesi and E. crossopterum. Our results suggest that sympatry of the two species in the western upper Caney Fork system is a potential threat to the persistence of E. forbesi.

Meristic data description: 

Meristic data tables for both Etheostoma forbesi and Etheostoma crossopterum are attached ("E_forbesi_meristic_data.csv" and "E_crossopterum_meristic_data.csv"). Data are presented as one row of data representing each individual. Museum identification numbers for each individual examined are listed in column 1 of each table. The locality information for each museum lot number from column 1 of the meristic data tables can be found in the corresponding locality data files ("E_forbesi_meristic_locality_data.csv", "E_crossopterum_meristic_locality_data.csv").

Genetic data description:

Supplementary Materials A and B (files "Supplementary_Material_A.csv" and "Supplementary_Material_B.csv") are tables listing the Genbank accession numbers, tissue and whole-body museum accession numbers, and geographic collection locality information for each DNA sequence used in this study. 

Alignments of mitochondrial cytb and nuclear S7 sequence data are provided in nexus file format (files: "spottail_cytb_alignment.nex" and "spottail_s7_alignment.nex").