Andrew R. Henderson | Geology Reports

USGS2025

A hidden heelsplitter: Distribution of an undescribed endemic freshwater mussel in the Barrens Plateau

Malacologists generally acknowledge that the Alasminota holstonia (Tennessee Heelsplitter) populations in the Caney Fork, Elk, and Duck river drainages in the Barrens Plateau region of middle Tennessee likely represent a closely related, but distinct, species, collectively referred to as Alasminota sp. (Barrens Heelsplitter). Recent surveys indicate that the species persists in at least 5 streams: Collins River, Pocahontas Branch, Witty Creek, and Pepper Hollow Branch in the Caney Fork River drainage and Little Duck River in the Duck River drainage, with evidence of recruitment in 2 of these streams. These findings suggest a restricted distribution and highlight the need for taxonomic assessment through genetic analysis. If elevated to species status, the Barrens Heelsplitter would represent a narrow endemic that may require conservation attention, underscoring the ecological significance of Tennessee's Barrens Plateau Region.

Tennessee↗

USGS2023

Glacial vicariance and secondary contact shape demographic histories in a freshwater mussel species complex

Characterizing the mechanisms influencing the distribution of genetic variation in aquatic species can be difficult due to the dynamic nature of hydrological landscapes. In North America’s Central Highlands, a complex history of glacial dynamics, long-term isolation, and secondary contact have shaped genetic variation in aquatic species. Although the effects of glacial history have been demonstrated in many taxa, responses are often lineage- or species-specific and driven by organismal ecology. In this study, we reconstruct the evolutionary history of a freshwater mussel species complex using a suite of mitochondrial and nuclear loci to resolve taxonomic and demographic uncertainties. Our findings do not support Pleurobema rubrum as a valid species, which is proposed for listing as threatened under the U.S. Endangered Species Act. We synonymize P. rubrum under Pleurobema sintoxia —a common and widespread species found throughout the Mississippi River Basin. Further investigation of patterns of genetic variation in P. sintoxia identified a complex demographic history, including ancestral vicariance and secondary contact, within the Eastern Highlands. We hypothesize these patterns were shaped by ancestral vicariance driven by the formation of Lake Green and subsequent secondary contact after the last glacial maximum. Our inference aligns with demographic histories observed in other aquatic taxa in the region and mirrors patterns of genetic variation of a freshwater fish species ( Erimystax dissimilis ) confirmed to serve as a parasitic larval host for P. sintoxia . Our findings directly link species ecology to observed patterns of genetic variation and may have significant implications for future conservation and recovery actions of freshwater mussels.

Mississippi River basin↗