Nathan A Johnson
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
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
Freshwater mussels of the family Unionidae, also known as naiads, pearly mussels, freshwater clams, or unionids, are a diverse group of bivalve mollusks that are distributed on every continent except Antarctica. Approximately 300 species are known from the United States, with most of this diversity residing in rivers of the Southeast where many endemic taxa have evolved.
Life History Characterization and Host Fish Identification for Federally Listed and Imperiled Freshwater Mussel Species in the Suwannee River Basin in Georgia and Florida
Freshwater mussels are considered the most imperiled group of animals in the United States. These animals provide valuable ecological services by filtering water, sequestering nutrients, and providing forage for migratory birds, small mammals, and turtles. They also have a unique and complex life cycle that makes them especially vulnerable to human disturbances. It includes a parasitic larval...
The Conasauga River in northwest Georgia and southeast Tennessee harbors the majority of mussel diversity still found in the Georgia portion of the Upper Coosa Basin. While the Conasauga historically supported at least 44 mussel species, only about 20 species remain.
Integrative taxonomy resolves taxonomic uncertainty for freshwater mussels being considered for protection under the U.S. Endangered Species Act
Objectively delimiting species boundaries remains an important challenge in systematics and becomes urgent when unresolved taxonomy complicates conservation and recovery efforts. We examined species boundaries in the imperiled freshwater mussel genus Cyclonaias(Bivalvia: Unionidae) using morphometrics, molecular phylogenetics, and...Johnson, Nathan A.; Smith, Chase H.; Pfeiffer, John M.; Randklev, Chalres R.; Williams, James D.; Austin, James D.
Cytonuclear discordance in the Florida Everglades invasive Burmese python (Python bivittatus) population reveals possible hybridization with the Indian python (P. molurus)
The invasive Burmese python (Python bivittatus) has been reproducing in the Florida Everglades since the 1980s. These giant constrictor snakes have caused a precipitous decline in small mammal populations in southern Florida following escapes or releases from the commercial pet trade. To better understand the invasion pathway and genetic...Hunter, Margaret E.; Johnson, Nathan A.; Smith, Brian J.; Davis, Michelle C.; Butterfield, John S.; Snow, Ray W.; Hart, Kristen M.
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...Johnson, Nathan A.; Schofield, Pamela; Williams, James D.; Austin, James D.
A semi-arid river in distress: Contributing factors and recovery solutions for three imperiled freshwater mussels (Family Unionidae) endemic to the Rio Grande basin in North America
Freshwater resources in arid and semi-arid regions are in extreme demand, which creates conflicts between needs of humans and aquatic ecosystems. The Rio Grande basin in the southwestern United States and northern Mexico exemplifies this issue, as much of its aquatic biodiversity is in peril as a result of human activities. Unionid mussels have...Randklev, Charles R.; Miller, Tom; Hart, Michael; Morton, Jennifer; Johnson, Nathan A.; Skow, Kevin; Inoue, Kentaro; Tsakiris, Eric; Oetker, Susan; Smith, Ryan; Robertson, Clint; Lopez, Roel
Cumulative spring discharge and survey effort influence occupancy and detection of a threatened freshwater mussel, the Suwannee Moccasinshell
Freshwater mussels (Unionidae) are among the most imperiled groups of organisms in the world, and the lack of information regarding species distributions, life-history characteristics, and ecological and biological requirements may limit the protection of remaining mussel populations. We examined the influence of hydrologic factors on the...Holcomb, Jordan M.; Shea, Colin P.; Johnson, Nathan A.
Molecular and morphometric analyses reveal cryptic diversity within freshwater mussels (Bivalvia: Unionidae) of the western Gulf coastal drainages of the USA
Past geological processes and climate change affected current species distributions and the genetic structure of riverine fauna. Western Gulf of Mexico coastal rivers harbour four mussel species within the genus Fusconaia(Bivalvia: Unionida). The distributions of these species are unclear owing to their indistinguishable shell morphologies....Pieri, Anna M.; Inoue, Kentaro; Johnson, Nathan A.; Smith, Chase H.; Harris, John L.; Robertson, Clint; Randklev, Charles R.
Molecular and morphological data reveal non-monophyly and speciation in imperiled freshwater mussels (Anodontoides and Strophitus)
Accurate taxonomic placement is vital to conservation efforts considering many intrinsic biological characteristics of understudied species are inferred from closely related taxa. The rayed creekshell, Anodontoides radiatus (Conrad, 1834), exists in the Gulf of Mexico drainages from western Florida to Louisiana and has been petitioned for listing...Smith, Chase H.; Johnson, Nathan A.; Pfeiffer, John M.; Gangloff, Michael M.
Molecular phylogeny of the Nearctic and Mesoamerican freshwater mussel genus Megalonaias
Megalonaias is the most geographically widespread genus of the subfamily Ambleminae and is distributed across much of the eastern half of North America, from Minnesota to Nicaragua. Despite the large geographic distribution, the species-level diversity of Megalonaias is quite depauperate (2 spp.), suggesting the genus may not be...Pfeiffer, John M.; Sharpe, Ashley; Johnson, Nathan A.; Emery, Kitty F.; Page, Lawrence M.
Deciphering the link between doubly uniparental inheritance of mtDNA and sex determination in bivalves: Clues from comparative transcriptomics
Bivalves exhibit an astonishing diversity of sexual systems and sex-determining mechanisms. They can be gonochoric, hermaphroditic or androgenetic, with both genetic and environmental factors known to determine or influence sex. One unique sex-determining system involving the mitochondrial genome has also been hypothesized to exist in bivalves...Capt, Charlotte; Renaut, Sébastien; Ghiselli, Fabrizio; Milani, Liliana; Johnson, Nathan A.; Sietman, Bernard E.; Stewart, Donald; Breton, Sophie
The Pleurobemini (Bivalvia: Unionida) revisited: Molecular species delineation using a mitochondrial DNA gene reveals multiple conspecifics and undescribed species
The Pleurobemini (Bivalvia: Unionida) represent approximately one-third of freshwater mussel diversity in North America. Species identification within this group is challenging due to morphological convergence and phenotypic plasticity. Accurate species identification, including characterisation of currently unrecognised taxa, is required to...Inoue, Kentaro; Hayes, David M.; Harris, John L.; Johnson, Nathan A.; Morrison, Cheryl L.; Eackles, Michael S.; King, Tim; Jones, Jess W.; Hallerman, Eric M.; Christian, Alan D.; Randklev, Charles R.
A revised list of the freshwater mussels (Mollusca: Bivalvia: Unionida) of the United States and Canada
We present a revised list of freshwater mussels (order Unionida, families Margaritiferidae and Unionidae) of the United States and Canada, incorporating changes in nomenclature and systematic taxonomy since publication of the most recent checklist in 1998. We recognize a total of 298 species in 55 genera in the families Margaritiferidae (one genus...Williams, James D.; Bogan, Arthur E.; Butler, Robert S.; Cummings, Kevin S.; Garner, Jeffrey T.; Harris, John L.; Johnson, Nathan A.; Watters, G. Thomas
The extremely divergent maternally- and paternally-transmitted mitochondrial genomes are co-expressed in somatic tissues of two freshwater mussel species with doubly uniparental inheritance of mtDNA
Freshwater mussel species with doubly uniparental inheritance (DUI) of mtDNA are unique because they are naturally heteroplasmic for two extremely divergent mtDNAs with ~50% amino acid differences for protein-coding genes. The paternally-transmitted mtDNA (or M mtDNA) clearly functions in sperm in these species, but it is still unknown whether it...Breton, Sophie; Bouvet, Karim; Auclair, Gabrielle; Ghazal, Stephanie; Sietman, Bernard E.; Johnson, Nathan A.; Bettinazzi, Stefano; Dtewart, Donald T.; Guerra, Davide