Nathan A Johnson, Ph.D.
Nathan Johnson is a Research Biologist at the USGS Wetland and Aquatic Research Center.
EDUCATION
Ph.D., Fisheries and Aquatic Sciences, University of Florida
M.S., Fisheries and Wildlife Sciences, Virginia Tech University
B.S., Fisheries Science, Virginia Tech University
RESEARCH
Nathan Johnson's research focuses on investigating species boundaries, distributions, and conservation priorities of freshwater mussels in the Southeast. Raised in eastern Virginia, Nate received both his bachelor’s and master’s degrees from the Fisheries and Wildlife Department at Virginia Tech and earned his Ph.D. at the University of Florida. His undergraduate research focused on conservation genetics and propagation of endangered freshwater mussels and fishes. For his master’s, Nate looked at the genetics of disease resistance in rainbow trout at the USDA-National Center for Cool and Coldwater Aquaculture in Leetown, WV. By developing new molecular markers to trace pedigrees and populations structure, he identified associations between major histocompatibility genes and disease resistance. His dissertation research resolved long-standing uncertainties about the systematics of freshwater mussels that will aid in the development of more effective conservation management strategies. This includes documenting mussel diversity in rivers of the North American Coastal Plain using DNA barcoding and evaluating the processes responsible for their current geographic distribution (phylogeography). He is active in a variety of professional societies including the American Fisheries Society and the Freshwater Mollusk Conservation Society and currently partnered with the Florida Museum, the Smithsonian Institute, Florida Fish and Wildlife Conservation Commission, and the US Fish and Wildlife Service. Outside of professional interests, he enjoys traveling, mountain biking, fishing, and surfing.
Science and Products
Salinity tolerance among three freshwater mussels (Bivalvia: Unionidae) from Gulf Coastal Plain drainages
Molecular and morphological data on two species complexes in the freshwater mussel genus Cyclonaias
Genetics rayed creekshell
Cumulative spring discharge and survey effort influence threatened Suwannee moccasinshell, Medionidus walkeri, occupancy and detection
Characterizing the early life history of an imperiled freshwater mussel (Ptychobranchus jonesi)
Rediscovery and genetic confirmation of the Threeridge Mussel, Amblema plicata (Say, 1817) (Bivalvia, Unionidae), in the Choctawhatchee River, Florida, USA
Gulf Coast vicariance shapes phylogeographic history of a North American freshwater mussel species complex
Genetic and morphological characterization of the freshwater mussel clubshell species complex (Pleurobema clava and Pleurobema oviforme) to inform conservation planning
Resolving species boundaries in the critically imperiled freshwater mussel species, Fusconaia mitchelli (Bivalvia: Unionidae)
Novel molecular resources to facilitate future genetics research on freshwater mussels (Bivalvia: Unionidae)
The utility of zooarchaeological data to guide listing efforts for an imperiled mussel species (Bivalvia: Unionidae: Pleurobema riddellii)
A new species of freshwater mussel in the genus Popenaias Frierson, 1927, from the Gulf coastal rivers of central Mexico (Bivalvia: Unionida: Unionidae) with comments on the genus
A comparative phylogeographic approach to facilitate recovery of an imperiled freshwater mussel (Bivalvia: Unionida: Potamilus inflatus)
Comparative phylogenomics reveal complex evolution of life history strategies in a clade of bivalves with parasitic larvae (Bivalvia: Unionoida: Ambleminae)
Standardizing a non-lethal method for characterizing the reproductive status and larval development of freshwater mussels (Bivalvia: Unionoida)
Putative mitochondrial sex determination in the Bivalvia: Insights from a hybrid transcriptome assembly in freshwater mussels
Integrative taxonomy reveals a new species of freshwater mussel, Potamilus streckersoni sp. nov. (Bivalvia: Unionidae): Implications for conservation and management
Non-USGS Publications**
**Disclaimer: The views expressed in Non-USGS publications are those of the author and do not represent the views of the USGS, Department of the Interior, or the U.S. Government.
Science and Products
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Filter Total Items: 18
Salinity tolerance among three freshwater mussels (Bivalvia: Unionidae) from Gulf Coastal Plain drainages
An important physiological constraint influencing distributions of coastal freshwater organisms is their tolerance for saline conditions. We experimentally evaluated salinity tolerance for three freshwater mussel species (Utterbackia imbecillis, Elliptio jayensis, and Glebula rotundata). Mussels were transferred abruptly from well water to one of five treatments (0 [control], 6, 12, 18 or 24 partsMolecular and morphological data on two species complexes in the freshwater mussel genus Cyclonaias
We examined species boundaries within an imperiled group of freshwater mussels in the genus Cyclonaias (Bivalvia: Unionidae) using morphometrics, molecular phylogenetics, and multispecies coalescent models to help guide pending conservation assessments and legislative decisions. Congruence across all lines of evidence indicated that current taxonomy overestimates diversity in the C. pustulosa specGenetics rayed creekshell
This dataset supports the inclusion of Anodontoides radiatus in the genus Strophitus, introducing the binomial Strophitus radiatus. These data also provide strong support for paraphyly in Strophitus and advocate the resurrection of the genus Pseudodontoides to represent the binomials Pseudodontoides connasaugaensis and Pseudodontoides subvexus.Cumulative spring discharge and survey effort influence threatened Suwannee moccasinshell, Medionidus walkeri, occupancy and detection
Freshwater mussels (Unionidae) are among the most imperiled groups of organisms in the world. Unionids are plagued with a lack of basic information regarding species distributions, life history characteristics, and ecological and biological requirements. We assessed the influence of hydrologic factors on the occurrence of the Suwannee Moccasinshell, Medionidus walkeri, a federally threatened freshCharacterizing the early life history of an imperiled freshwater mussel (Ptychobranchus jonesi)
Conservation of imperiled species is frequently challenged by insufficient knowledge of life history and the environmental factors that affect various life stages. The larvae (glochidia) of most freshwater mussels in the family Unionidae are obligate ectoparasites of fishes. We describe the early life history of the federally endangered Southern Kidneyshell, Ptychobranchus jonesi, and compare meth - Multimedia
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Filter Total Items: 48
Rediscovery and genetic confirmation of the Threeridge Mussel, Amblema plicata (Say, 1817) (Bivalvia, Unionidae), in the Choctawhatchee River, Florida, USA
Recent freshwater mussel research has resulted in rediscovery of several species presumed extinct. We report the rediscovery of Amblema plicata (Say, 1817) in 2019 from the Choctawhatchee River, Florida, USA. Amblema plicata has not been reported in the Choctawhatchee river basin since 1958, more than 61 years ago. This species was collected during the long-term monitoring of freshwater mussels inAuthorsLauren N. Patterson, Susan R. Geda, Nathan A. JohnsonGulf Coast vicariance shapes phylogeographic history of a North American freshwater mussel species complex
AimFreshwater mussels share habitat and are parasites of freshwater fishes during the larval life stage. Therefore, models of fish biogeography may also explain the historical biogeography of freshwater mussels. We tested this assumption using predictions of three biogeographic models constructed for northern Gulf of Mexico drainages on a freshwater mussel species complex. Specifically, we testedAuthorsSean M. Keogh, Nathan Johnson, James D. Williams, Charles R. Randklev, Andrew SimonsGenetic and morphological characterization of the freshwater mussel clubshell species complex (Pleurobema clava and Pleurobema oviforme) to inform conservation planning
The shell morphologies of the freshwater mussel species Pleurobema clava (federally endangered) and Pleurobema oviforme (species of concern) are similar, causing considerable taxonomic confusion between the two species over the last 100 years. While P. clava was historically widespread throughout the Ohio River basin and tributaries to the lower Laurentian Great Lakes, P. oviforme was confined toAuthorsCheryl Morrison, Nathan A. Johnson, Jess W Jones, Michael S. Eackles, Aaron Aunins, Daniel Bruce Fitzgerald, Eric M. Hallerman, Timothy L. KingResolving species boundaries in the critically imperiled freshwater mussel species, Fusconaia mitchelli (Bivalvia: Unionidae)
Species are a fundamental unit of biology, and defining accurate species boundaries is integral to effective conservation and management of imperiled taxa. Freshwater mussels (Bivalvia: Unionidae) are among the most imperiled groups of organisms in North America, yet species boundaries remain uncertain for many taxa. The False Spike, Fusconaia mitchelli (Simpson in Dall, 1895), is a freshwater musAuthorsChase H. Smith, Nathan Johnson, Kaitlyn Havlik, Robert D. Doyle, Charles R. RandklevNovel molecular resources to facilitate future genetics research on freshwater mussels (Bivalvia: Unionidae)
Molecular data have been an integral tool in the resolution of the evolutionary relationships and systematics of freshwater mussels, despite the limited number of nuclear markers available for Sanger sequencing. To facilitate future studies, we evaluated the phylogenetic informativeness of loci from the recently published anchored hybrid enrichment (AHE) probe set Unioverse and developed novel SanAuthorsNathan A. Johnson, Chase H. SmithThe utility of zooarchaeological data to guide listing efforts for an imperiled mussel species (Bivalvia: Unionidae: Pleurobema riddellii)
The status of species in freshwater systems shift over time due to natural and anthropogenic causes. Determining the magnitude and cause of these shifts requires a long-term perspective. This process is complicated when there are also questions about the taxonomic validity of a species. Addressing these issues is important because both can undermine conservation and management efforts if incorrectAuthorsCharles R. Randklev, Steve Wolverton, Nathan A. Johnson, Chase H. Smith, Traci DuBose, Clint Robertson, Julian ConleyA new species of freshwater mussel in the genus Popenaias Frierson, 1927, from the Gulf coastal rivers of central Mexico (Bivalvia: Unionida: Unionidae) with comments on the genus
The Gulf coastal drainages of central Mexico are a faunal transition zone between North and South America and harbor a unique assemblage of freshwater mussels (Bivalvia: Unionida). However, little information is available regarding the taxonomy, distribution, and evolutionary history of the Mexican mussel fauna due to limited sampling over the last 100 years. To address these knowledge gaps, we evAuthorsKentaro Inoue, Kevin S. Cummings, Jeremy S. Tiemann, Thomas D. Miller, Nathan Johnson, Chase H. Smith, Charles R. RandklevA comparative phylogeographic approach to facilitate recovery of an imperiled freshwater mussel (Bivalvia: Unionida: Potamilus inflatus)
North American freshwaters are among the world’s most threatened ecosystems, and freshwater mussels are among the most imperiled inhabiting these systems. A critical aspect of conservation biology is delineating patterns of genetic diversity, which can be difficult when a taxon has been extirpated from a significant portion of its historical range. In such cases, evaluating conservation and recoveAuthorsChase H. Smith, Nathan A. JohnsonComparative phylogenomics reveal complex evolution of life history strategies in a clade of bivalves with parasitic larvae (Bivalvia: Unionoida: Ambleminae)
Freshwater mussels are a species‐rich group with biodiversity patterns strongly shaped by a life history strategy that includes an obligate parasitic larval stage. In this study, we set out to reconstruct the life history evolution and systematics in a clade of freshwater mussels adapted to parasitizing a molluscivorous host fish. Anchored hybrid enrichment and ancestral character reconstruction rAuthorsChase H. Smith, John M. Pfeiffer, Nathan A. JohnsonStandardizing a non-lethal method for characterizing the reproductive status and larval development of freshwater mussels (Bivalvia: Unionoida)
Actively monitoring the timing, development, and reproductive patterns of endangered species is critical when managing for population recovery. Freshwater mussels are among the most imperiled organisms in the world, but information about early larval (glochidial) development and brooding periods is still lacking for many species. Previous studies have focused on the complex life history stage whenAuthorsCaitlin Beaver, Susan Geda, Nathan JohnsonPutative mitochondrial sex determination in the Bivalvia: Insights from a hybrid transcriptome assembly in freshwater mussels
Bivalves exhibit an astonishing diversity of sexual systems, with genetic and environmental determinants of sex, and possibly the only example of mitochondrial genes influencing sex determination pathways in animals. In contrast to all other animal species in which strict maternal inheritance (SMI) of mitochondria is the rule, bivalves possess a system known as doubly uniparental inheritance (DUI)AuthorsCharlotte Capt, Sebastien Renaut, Donald Stewart, Nathan A. Johnson, Sophie BretonIntegrative taxonomy reveals a new species of freshwater mussel, Potamilus streckersoni sp. nov. (Bivalvia: Unionidae): Implications for conservation and management
Inaccurate systematics confound our ability to determine evolutionary processes that have led to the diversification of many taxa. The North American freshwater mussel tribe Lampsilini is one of the better-studied groups in Unionidae, however, many supraspecific relationships between lampsiline genera remain unresolved. Two genera previously hypothesized to be non-monophyletic that have been largeAuthorsChase H. Smith, Nathan Johnson, Kentaro Inoue, Robert Doyle, Charles R. RandklevNon-USGS Publications**
Grobler, P. J., Jones, J.W., Johnson, N.A., Neves, R.J., and E.M. Hallerman. 2011. Homogeneity at Nuclear Microsatellite Loci Masks Mitochondrial Haplotype Diversity in the Endangered Fanshell Pearlymussel (Cyprogenia stegaria). Journal of Heredity 102(2): 196-206. [Link]**Disclaimer: The views expressed in Non-USGS publications are those of the author and do not represent the views of the USGS, Department of the Interior, or the U.S. Government.