RECONSTRUCTING LATE PLIOCENE THROUGH EARLY PLEISTOCENE ANCESTRAL RIVER DRAINAGE BASINS IN THE INTERIOR LOW PLATEAU AND APPALACHIANS KARST REGIONS TO UNDERSTAND THE EVOLUTIONARY HISTORY OF TYPHLICHTHYS SUBTERRANEUS (PERCOPSIFORMES: AMBLYOPSIDAE)

Stratigraphic and hydrologic features can serve as barriers for cave animal distribution in karst. Two main karst regions exist in the Tennessee-Alabama-Georgia region, the Appalachian Valley and Ridge (AVR) and Interior Low Plateau (ILP). These regions are separated by a major fault zone along the eastern escarpment of the Cumberland Plateau. Very few cave species occur in both regions, which makes any animal that occurs in both regions significant. Typhlichthys subterraneus is a wide-ranging cavefish known from >180 caves in the ILP, with the greatest density in central TN and northern AL. This species was known previously from four caves in GA; however, in 2015, a population was found in Crane Cave, Catoosa Co., GA, well within the AVR and in a distinct watershed compared to previously documented populations. Molecular genetics previously identified 10 cryptic T. subterraneus lineages, with the most recent common ancestor among the lineages dating to the late Pliocene to early Pleistocene (3.5 to 2.1 Mya). The Crane Cave population is most closely related to a lineage comprised of populations from Little Sequatchie River Valley in TN, two northwestern GA caves, and from Wills Valley caves in AL. This Crane Cave T. subterraneus lineage diverged from other lineages in the ILP between 2.9 and 1.6 Mya, which predates the emergence of the Tennessee-Coosa River drainage divide that exists today. As such, the ancestor of the Crane Cave lineage must have existed when the ancestral Tennessee and Coosa Rivers formed the Appalachian River, and prior to uplift in the Southern Appalachians that caused downcutting by the ancestral Tennessee River through Walden Ridge, creation of a drainage divide between the Tennessee and Coosa Rivers, and eventual flow of the Tennessee River into the Sequatchie Valley. Based on divergence estimates of the Crane Cave lineage, the Tennessee-Coosa drainage divide was likely in place by the late Pliocene. This timing is also supported by cave sediment records. Continued uplift would have further isolated the Crane Cave AVR population from the ILP T. subterraneus lineages, with their divergences linked to the reorganization of the Tennessee River drainage basin throughout the Pleistocene in the ILP.