Geology topics

Nathan Johnson

Publications and source records attributed to Nathan Johnson.

21 records · Page 2Linked to original sources

USGS2019

A comprehensive approach uncovers hidden diversity in freshwater mussels (Bivalvia: Unionidae) with the description of a novel species

Major geological processes have shaped biogeographical patterns of riverine biota. The Edwards Plateau of central Texas, USA, exhibits unique aquatic communities and endemism, including several species of freshwater mussels. Lampsilis bracteata (Gould, 1855) is endemic to the Edwards Plateau region; however, its phylogenetic relationship with other species in the Gulf coastal rivers and Mississippi River basin is unknown. We evaluated phylogenetic relationships, shell morphologies and soft anatomy characters of L. bracteata and a closely related congener, Lampsilis hydiana (Lea, 1838) throughout their ranges. Our results showed the presence of an undescribed species: Lampsilis bergmanni sp.n. Lampsilis bracteata and L. bergmanni sp.n. share similar shell morphologies and soft anatomy characters; however, they are genetically distinct. Geological processes, such as faulting and sea‐level changes during the Miocene to Pliocene, are likely to have facilitated diversification of Lampsilis species, resulting in isolation of L. bracteata on the Edwards Plateau and diversification between L. bergmanni sp.n. and L. hydiana . We conclude that L. bracteata range is restricted to the Colorado River basin, whereas L. bergmanni sp.n. occurs only in upstream reaches of the Guadalupe River basin. Conservation actions are warranted for both species due to their restricted distributions and potential anthropogenic threats.

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USGS2017

Freshwater mussels (Unionidae): Central and West Texas Final Report

The goal of this study was two-fold: (1) assess the taxonomic identity and phylogenetic placement of Quadrula aurea (Golden Orb) [Federal Candidate], Quadrula houstonensis (Smooth Pimpleback) [Federal Candidate], and Quadrula petrina (Texas Pimpleback) [Federal Candidate] through mitochondrial and nuclear DNA sequencing; and (2) provided additional information on the distribution and abundance for mussel species petitioned for listing under ESA through field surveys in portions of several major rivers in Central and West Texas. The final report is organized by 4 research tasks as per contract (see Appendix A) and submitted proposals. Below is an outline of goal-oriented tasks for this project: Task 1 – Conduct comprehensive surveys of portions of the Brazos, Colorado, and Guadalupe River basins Task 2 – Conduct comprehensive surveys of portions of the Rio Grande Basin Task 3 – Develop conservation status assessment maps for 9 state-threatened mussel species in Texas Task 4 – Delineate species boundaries, test for cryptic species, and assess phylogenetic relationships for threatened Texas mussel species in the genus Quadrula Note the following 2 tasks were either not funded in the current contract or was a modification of the contract and added as a project deliverable: Task 5 – Delineate species boundaries, test for cryptic species, and assess phylogenetic relationships for east Texas mussel species in the genus Fusconaia (Not Funded) Task 6 – Evaluate the conservation status of Texas hornshell and other mussels in the Pecos and Devils Rivers (Contract amendment, results combined with Task 2). Detailed descriptions of the research tasks and findings are found within each chapter of the report. Here, we outline and summarize project deliverables and major findings for each task.

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USGS2013

Distribution of extant populations of Quadrula mitchelli (false spike)

The False Spike, Quadrula mitchelli (Simpson 1896), is a rare species of mussel endemic to Central Texas and the Rio Grande drainage (Howells 2010). This species was thought to have been extinct until the discovery of several live individuals in the Guadalupe River and a fresh dead individual in the San Saba River in 2011 (Randklev et al. 2012; Randklev et al. in press). Since then, this species has been reported at several other locations within its historic range (Sowards et al. in press; Tsakiris and Randklev 2013; Mabe and Kennedy 2013). Here, we report on the current known distribution of this species.

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