Natural Resources Institute Aquatic Ecosystems

Research

Mussel Research Group

Recent Publications

• 2019 | Systematics and Biodiversity Integrative taxonomy reveals a new species of freshwater mussel, Potamilus streckersoni sp. nov. (Bivalvia: Unionidae): implications for conservation and management
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  Integrative taxonomy reveals a new species of freshwater mussel, Potamilus streckersoni sp. nov. (Bivalvia: Unionidae): implications for conservation and management

  2019 | Systematics and Biodiversity
  https://doi.org/10.1080/14772000.2019.1607615
  Chase H. Smith, Nathan A. Johnson, Kentaro Inoue, Robert D. Doyle & Charles R. Randklev

  Abstract

  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 largely overlooked are Leptodea and Potamilus. We set out to resolve supraspecific relationships in Lampsilini and test the monophyly of Leptodea and Potamilus by integrating molecular, morphological, and life history data. Our molecular matrix consisted of four loci: cytochrome c oxidase subunit 1 (CO1), NADH dehydrogenase subunit 1 (ND1), internal transcribed spacer 1 (ITS1), and 28S ribosomal RNA. Secondly, we performed both traditional and Fourier shape morphometric analyses to evaluate morphological differences and finally, we compared our results with available life history data. Molecular data supported the paraphyly of both Leptodea and Potamilus, but nodal support was insufficient to make any conclusions regarding generic-level assignments at this time. In contrast, inference from our integrative taxonomic assessment depicts significant support for the recognition of a new species, Potamilus streckersoni sp. nov., the Brazos Heelsplitter. Our data show clear separation of three taxonomic entities in the P. ohiensis species complex: P. amphichaenus, P. ohiensis, and P. streckersoni sp. nov.; all molecularly, geographically, and morphologically diagnosable. Our findings have profound implications for unionid taxonomy and will aid stakeholders in establishing effective conservation and management strategies.

  Publication at https://doi.org/10.1080/14772000.2019.1607615

• 2019 | Aquatic Conservation Evaluating the upper thermal limits of glochidia for selected freshwater mussel species (Bivalvia: Unionidae) in central and east Texas, and the implications for their conservation
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  Evaluating the upper thermal limits of glochidia for selected freshwater mussel species (Bivalvia: Unionidae) in central and east Texas, and the implications for their conservation

  2019 | Aquatic Conservation
  https://doi.org/10.1002/aqc.3136
  Jennifer M. Khan, Michael Hart, Jack Dudding, Clinton R. Robertson, Roel Lopez, Charles R. Randklev

  Abstract

  1. Understanding the temperature tolerances of organisms is critical because the thermal regimes of freshwater ecosystems are changing globally. Native freshwater mussels are sensitive to increasing water temperatures because of their physiology and unique life history. Detailed knowledge on lethal temperatures for mussels has been limited to less than 5% of the species known to occur in North America, and little is known about the thermal tolerances of mussel species from rivers within the south‐western USA.
  2. To determine the effects of elevated water temperature on mussels, the upper thermal tolerances of larvae (glochidia) for the following species across four basins in Texas (Neches, Guadalupe, San Antonio, and Colorado) were tested: Amblema plicata, Cyclonaias necki, Fusconaia mitchelli, Lampsilis bracteata, Lampsilis hydiana, Lampsilis satura, Lampsilis teres, and Obovaria arkansasensis.
  3. Glochidia were acclimated to 27°C across a range of experimental temperatures (30–39°C) in 24‐h standard acute laboratory tests. The median lethal temperature (LT50) among glochidia averaged 32.4°C and ranged from 26.9 to 36.4°C.
  4. Thermal tolerances differed significantly among and within species, and by season. Comparing these results with current water temperatures in central and east Texas indicated that populations of the focal species studied are at risk from rising environmental temperatures and, as a consequence, their long‐term viability will be challenging in future years.

  Publication at https://doi.org/10.1002/aqc.3136

• 2019 | Cladistics A comprehensive approach uncovers hidden diversity in freshwater mussels (Bivalvia: Unionidae) with the description of a novel species
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  A comprehensive approach uncovers hidden diversity in freshwater mussels (Bivalvia: Unionidae) with the description of a novel species

  2019 | Cladistics
  https://doi.org/10.1111/cla.12386
  Kentaro Inoue, John L. Harris, Clinton R. Robertson, Nathan A. Johnson, Charles R. Randklev

  Abstract

  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. © The Willi Hennig Society 2019

  Publication at https://doi.org/10.1111/cla.12386

• 2019 | Freshwater Mollusk Biology and Conservation Host fish associations for two highly imperiled mussel species from the southwestern United States: cyclonaias necki (guadalupe orb) and fusconaia mitchelli (false spike)
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  Host fish associations for two highly imperiled mussel species from the southwestern United States: cyclonaias necki (guadalupe orb) and fusconaia mitchelli (false spike)

  2019 | Freshwater Mollusk Biology and Conservation
  22:12–19, 2019

  Jack Dudding, Michael Hart, Jennifer Khan, Clinton R. Robertson, Roel
  Lopez, and Charles R. Randklev

  Abstract

  Most freshwater mussels (Unionidae) require a specific host fish to advance their life cycle. Currently, hosts are known for only one-third of the mussel species endemic to the United States and Canada. Texas boasts the greatest diversity of freshwater mussels in the southwestern United States. However, information on mussel-host relationships for ~52 species known to occur within the state is either lacking or incomplete, including two species, Cyclonaias necki (Guadalupe Orb) and Fusconaia mitchelli (False Spike), currently under review for listing under the U.S. Endangered Species Act. To address this deficiency, we conducted laboratory trials that tested 12 fish species (four families and 11 genera) for C. necki and eight species (four families and seven genera) for F. mitchelli. For C. necki, we identified four host species, Ictalurus punctatus (Channel Catfish), Pylodictis olivarus (Flathead Catfish), Noturus gyrinus (Tadpole Madtom), and Ameiurus natalis (Yellow Bullhead). The transformation period was 11 to 22 d for I. punctatus (peak metamorphosis at 15 d), 16 d for P. olivaris and A. natalis, and 10 d for N. gyrinus. For F. mitchelli, we identified two host species, Cyprinella lutrensis (Red Shiner) and
  Cyprinella venusta (Blacktail Shiner); for both, the transformation period was 18 d. Current
  information on the status of these six host species within the Guadalupe River suggests that
  imperilment of C. necki and F. mitchelli may be partly related to the status of their host fishes. Our
  results also provide critical information for informing recovery activities, such as translocation and
  captive propagation, if deemed necessary for one or both mussel species.

  Full article here

• 2019 | Elsvier Salinity tolerance of a rare and endangered unionid mussel, Popenaias popeii (Texas Hornshell) and its implications for conservation and water management
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  Salinity tolerance of a rare and endangered unionid mussel, Popenaias popeii (Texas Hornshell) and its implications for conservation and water management

  2019 | Elsvier
  https://doi.org/10.1016/j.ecoenv.2018.11.031
  Michael A.Hart,Tom D.Miller, Charles R.Randklev

  Abstract
  Unionid mussels are considered sensitive to salinity and there is growing concern in arid and semi-arid regions that declining flows coupled with anthropogenic impacts are amplifying natural salinity levels. In this study, we tested the effects of varying salinity concentrations (3.0, 4.0, 5.0, 6.0, 7.0 and 10.0 ppt NaCl) on survival of adult Popenaias popeii, (Texas Hornshell). This species occurs in the Rio Grande basin of Texas and northern Mexico, an arid to semi-arid stream plagued by salinization, and was recently listed as Endangered under the U.S. Endangered Species Act. We performed 2, 4, and 10-day toxicity tests on individuals from two disjunct populations: Laredo, TX, and the Lower Canyons of the Rio Grande near Big Bend National Park. We found no significant differences in LC50 estimates between populations at 96-hrs or 10-days but significant differences in TUD50s at 5 ppt between populations, which indicates that tolerance does not vary but sensitivity may between these populations. Overlaying LC50 estimates at 10-days for both populations on plots of salinity (ppt) measured over time, we show parts of the Rio Grande periodically approach or exceed 4.0 ppt, indicating these reaches are becoming unsuitable for P. popeii and populations within them at risk.

  Full publication at https://www.sciencedirect.com/science/article/pii/S0147651318311679

• 2018 | Scientific Reports Integrative taxonomy resolves taxonomic uncertainty for freshwater mussels being considered for protection under the U.S. Endangered Species Act
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  Integrative taxonomy resolves taxonomic uncertainty for freshwater mussels being considered for protection under the U.S. Endangered Species Act

  2018 | Scientific Reports
  Scientific Reports volume 8, Article number: 15892 (2018)
  Nathan A. Johnson, Chase H. Smith, John M. Pfeiffer, Charles R. Randklev, James D. Williams, James D. Austin

  Abstract
  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 multispecies coalescent models to help guide pending conservation assessments and legislative decisions. Congruence across multiple lines of evidence indicated that current taxonomy overestimates diversity in the C. pustulosa species complex. The only genetically and morphologically diagnosable species in the C. pustulosa species complex were C. pustulosa and C. succissa and we consider C. aurea, C. houstonensis, C. mortoni, and C. refulgens to be synonyms of C. pustulosa. In contrast, all three species in the C. nodulata complex (C. necki, C. nodulata, and C. petrina) were genetically, geographically, and morphologically diagnosable. Our findings have important conservation and management implications, as three nominal species (C. aurea, C. houstonensis, and C. petrina) are being considered for protection under the Endangered Species Act.

  Full publication at https://www.nature.com/articles/s41598-018-33806-z

• 2018 | Global Ecology and Conservation The effect of dewatering on freshwater mussel (Unionidae) community structure and the implications for conservation and water policy: A case study from a spring-fed stream in the southwestern United States
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  The effect of dewatering on freshwater mussel (Unionidae) community structure and the implications for conservation and water policy: A case study from a spring-fed stream in the southwestern United States

  2018 | Global Ecology and Conservation
  https://doi.org/10.1016/j.gecco.2018.e00456

  Charles R.Randklev; Eric T.Tsakris; Matthew S.Johnson; Traci Popejoy; Michael A.Hart; Jennifer Khan; Dakus Geeslin; Clinton R. Robertson

  Abstract
  The availability of freshwater to meet human and natural ecosystem needs remains the ultimate challenge of ecologically sustainable water management. This issue is particularly true in the southwestern United States, such as Texas, where water resources are already over allocated. The San Saba River, located in central Texas, exemplifies this issue as excessive water withdrawal has resulted in intermittency for as much as two-thirds of its length. The effect of this dewatering on aquatic species such as mussels is not well known, which is problematic because five species of high conservation concern occur in this river. The goal of this study was to examine how dewatering may have affected the distribution of these species and to identify options for mitigating this threat. Comparing species-per-unit-effort (SPUE) and catch-per-unit-effort (CPUE) between these reaches, we found SPUE and CPUE were 3.7 and 7.9 times lower, respectively, in intermittent reaches than in perennial reaches. Using fuzzy ordination, we found that mussel assemblage structure differed between intermittent and perennial reaches despite both historically sharing similar fauna. Evaluating habitat, we found differences in mussel-mesohabitat associations between perennial and intermittent reaches. Current water policy and regulatory tools to mitigate this issue are insufficient, which raises serious questions about how states like Texas, located in arid and semi-arid regions, will be able to protect aquatic ecosystems under the specter of ever increasing population growth and climate change.

  Full publication available at https://www.sciencedirect.com/science/article/pii/S2351989418301690

• 2018 | PLOS One Misidentification of sex for Lampsilis teres, Yellow Sandshell, and its implications for mussel conservation and wildlife management
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  Misidentification of sex for Lampsilis teres, Yellow Sandshell, and its implications for mussel conservation and wildlife management

  2018 | PLOS One
  https://doi.org/10.1371/journal.pone.0197107

  Megan C. Hess, Kentaro Inoue, Eric T. Tsakiris, Michael Hart, Jennifer Morton,
  Jack Dudding, Clinton R. Robertson, Charles R. Randklev

  Abstract
  Correct identification of sex is an important component of wildlife management because changes in sex ratios can affect population viability. Identification of sex often relies on external morphology, which can be biased by intermediate or nondistinctive morphotypes and observer experience. For unionid mussels, research has demonstrated that species misidentification is common but less attention has been given to the reliability of sex identification. To evaluate whether this is an issue, we surveyed 117 researchers on their ability to correctly identify sex of Lampsilis teres (Yellow Sandshell), a wide ranging, sexually dimorphic species. Personal background information of each observer was analyzed to identify factors that may contribute to misidentification of sex. We found that median misidentification rates were ~20% across males and females and that observers falsely identified the number of female specimens more often (~23%) than males (~10%). Misidentification rates were partially explained by geographic region of prior mussel experience and where observers learned how to identify mussels, but there remained substantial variation among observers after controlling for these factors. We also used three morphometric methods (traditional, geometric, and Fourier) to investigate whether sex could be more correctly identified statistically and found that misidentification rates for the geometric and Fourier methods (which characterize shape) were less than 5% (on average 7% and 2% for females and males, respectively). Our results show that misidentification of sex is likely common for mussels if based solely on external morphology, which raises general questions, regardless of taxonomic group, about its reliability for conservation efforts.

  Full publication available at http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0197107

• 2018 | Invertebrate Systematics The Pleurobemini (Bivalvia : Unionida) revisited: molecular species delineation using a mitochondrial DNA gene reveals multiple conspecifics and undescribed species
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  The Pleurobemini (Bivalvia : Unionida) revisited: molecular species delineation using a mitochondrial DNA gene reveals multiple conspecifics and undescribed species

  2018 | Invertebrate Systematics
  32, 689–702
  https://doi.org/10.1071/IS17059

  Kentaro Inoue, David M. Hayes, John L. Harris, Nathan A. Johnson,
  Cheryl L. Morrison, Michael S. Eackles , Tim L. King, Jess W. Jones,
  Eric M. Hallerman, Alan D. Christian and Charles R. Randklev

  Abstract
  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 develop effective conservation strategies because many species in the group are imperiled. We examined 575 cox1 sequences from 110 currently recognised species (including 13 Fusconaia and 21 Pleurobema species) to understand phylogenetic relationships among pleurobemine species (mainly Fusconaia and Pleurobema) and to delineate species boundaries. The results of phylogenetic analyses showed no geographic structure within widespread species and illustrated a close relationship between Elliptio lanceolata and Parvaspina collina. Constraint tests supported monophyly of the genera Fusconaia and Pleurobema, including the subgenus P. (Sintoxia). Furthermore, results revealed multiple conspecifics, including P. hanleyianum and P. troschelianum, P. chattanoogaense and P. decisum, P. clava and P. oviforme, P. rubrum and P. sintoxia, F. askewi and F. lananensis, and F. cerina and F. flava. Species delimitation analyses identified three currently unrecognised taxa (two in Fusconaia and one in Pleurobema). Further investigation using additional genetic markers and other lines of evidence (e.g. morphology, life history, ecology) are necessary before any taxonomic changes are formalised.

  Full publication available at https://pubs.er.usgs.gov/publication/70195456

• 2018 | Science of the Total Environment 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.
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  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.

  2018 | Science of the Total Environment
  1;631-632:733-744
  doi: 10.1016/j.scitotenv.2018.03.032.

  Charles R. Randklev, Tom Miller, Michael Hart, Jennifer Morton, Nathan A. Johnson, Kevin Skowa,
  Kentaro Inoue, Eric T. Tsakiris, Susan Oetker, Ryan Smith, Clint Robertson, Roel Lopez

  Abstract
  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 been disproportionately impacted, though the specific factors responsible for their decline remain largely unknown. This is problematic because the Rio Grande basin harbors one federally endangered unionid mussel (Popenaias popeii, Texas Hornshell) plus two other mussel species (Potamilus metnecktayi, Salina Mucket; and Truncilla cognata, Mexican Fawnsfoot), which are also being considered for listing under the U.S. Endangered Species Act. To date, surveys for these species have not corrected for variability in detection so current range estimates may be inaccurate. Using single occupancy-modeling to estimate detection and occupancy at 115 sites along ~800 river kilometers of the Rio Grande in Texas, we found that detection probabilities were relatively high, indicating that our survey design was efficient. In contrast, the estimated occupancy was low, indicating that our focal species were likely rare within the Rio Grande drainage. In general, the predicted occupancy of our focal species was low throughout their respective ranges, indicating possible range declines. A comparison of currently occupied ranges to presumptive ranges underscores this point. The best-approximating models indicated that occupancy was influenced by habitat, water quantity and quality, and proximity to large-scale human activities, such as dams and major urban centers. We also discuss a series of conservation options that may not only improve the long-term prognosis of our focal species but also other aquatic taxa.

  Full publication available at https://www.ncbi.nlm.nih.gov/pubmed/29544177