Charles R. Randklev

Generic reclassification and species boundaries in the rediscovered freshwater mussel ‘ Quadrula’ mitchelli (Simpson in Dall, 1896)

The Central Texas endemic freshwater mussel, Quadrula mitchelli (Simpson in Dall, 1896), had been presumed extinct until relict populations were recently rediscovered. To help guide ongoing and future conservation efforts focused on Q. mitchelli we set out to resolve several uncertainties regarding its evolutionary history, specifically its unknown generic position and untested species boundaries. We designed a molecular matrix consisting of two loci (cytochrome c oxidase subunit I and internal transcribed spacer I) and 57 terminal taxa to test the generic position of Q. mitchelli using Bayesian inference and maximum likelihood phylogenetic reconstruction. We also employed two Bayesian species validation methods to test five a priori species models (i.e. hypotheses of species delimitation). Our study is the first to test the generic position of Q.mitchelli and we found robust support for its inclusion in the genus Fusconaia. Accordingly, we introduce the binomial, Fusconaia mitchelli comb. nov., to accurately represent the systematic position of the species. We resolved F. mitchelli individuals in two well supported and divergent clades that were generally distinguished as distinct species using Bayesian species validation methods, although alternative hypotheses of species delineation were also supported. Despite strong evidence of genetic isolation within F. mitchelli, we do not advocate for species-level status of the two clades as they are allopatrically distributed and no morphological, behavioral, or ecological characters are known to distinguish them. These results are discussed in the context of the systematics, distribution, and conservation of F. mitchelli.

The influence of stream discontinuity and life history strategy on mussel community structure: a case study from the Sabine River, Texas

The impoundment of running waters is a threat to freshwater mussels and has only been cursorily examined in Texas. To address this, we evaluate mussel assemblage structure in the Sabine River downstream of a flood control and hydropower reservoir. We use the serial discontinuity concept (SDC) and the Life History Continuum model (LHCM) to explain relationships between stream position (i.e., downstream distance from either dam) and mussel species richness, catch-per-unit effort (CPUE), and life history strategy. Using 90th, 85th, and 80th quantile regression models, we observed that mussel species richness and abundance were reduced for stream segments located near Lake Tawakoni and Toledo Bend Reservoir and that these reductions decreased with distance from either reservoir. We also observed significant shifts in life history composition of mussel assemblages depending on stream position from either dam. Opportunistic strategists were more abundant in reaches located immediately downstream of Lake Tawakoni and Toledo Bend Reservoir whereas periodic and equilibrium strategists were most abundant in reaches located at intermediate distances from either reservoir. Findings from this study confirm the negative impact large impoundments have on downstream mussel populations and demonstrate the value of using the SDC and LHCM for evaluating mussel response to river impoundment.

Is False Spike, Quadrula mitchelli (Bivalvia: Unionidae), Extinct? First Account of a Very Recently Deceased Individual in Over Thirty Years

Abstract A recent survey of the San Saba River in San Saba County, Texas, has yielded the first record in >30 years of a very recently deceased individual (i.e., with tissue present within the shell) of the unionid mussel Quadrula mitchelli (false spike). This very recently dead individual suggests that living populations of Q. mitchelli might still exist in the San Saba River. Our results provide evidence that surveys in remote areas may help to locate populations of rare species of unionid mussels. Resumen Un muestreo recién del río San Saba en el condado de San Saba, Texas, ha dado el primer registro en >30 años de un individuo de mejillón unionido Quadrula mitchelli recientemente fallecido (es decir, con el tejido aún presente dentro de la concha). El encuentro sugiere que aún podrían existir más poblaciones actuales de Q. mitchelli dentro del río San Saba. Nuestros resultados rinden evidencia que muestreos realizados dentro de áreas remotas podrían ayudar a localizar poblaciones de especies raras del mejillón unionido.

False Spike, Quadrula mitchelli (Bivalvia: Unionidae), is Not Extinct: First Account of a Live Population in Over 30 Years

Abstract. During a recent survey a small population of Quadrula mitchelli (Simpson, 1895), a species thought to have been extinct, was discovered in Texas. In total, 7 live individuals were collected from the Guadalupe River near Gonzales, Gonzales County, Texas. Our finding represents the only known population for this species in Texas and the first record of live specimens in over 30 y, which is significant because this species is currently under review for protection under the Endangered Species Act.

Conservation implications of late Holocene freshwater mussel remains of the Leon River in central Texas

Zooarchaeology is the study of animal remains (bone, shell, antler, and other organic tissues) from archaeological sites, which can provide conservation biologists with data on human–environmental interactions with greater time depth than historical records. Such data are of interest because they can be used to study whether or not contemporary animal communities (in this case of freshwater mussels) have changed in terms of species composition or range as a result of human-induced changes to habitat, which is essential for determining a species’ conservation status and formulating actions to protect remaining populations. This study considers whether or not the taxonomic composition of the freshwater mussel community from the Leon River in central Texas differs between the late Holocene and today. Specifically, we analyzed two zooarchaeological assemblages and compared those results with recent surveys conducted within the Leon River. Three species proposed for listing under the Endangered Species Act are found in the zooarchaeological record, of which two are now extirpated from the river basin (Truncilla macrodon and Fusconaia mitchelli). The results of this study provide an example of how zooarchaeological data can be used to evaluate mussel community change through time and provide evidence of range curtailment for threatened mussel species.

Archaeological Data Indicate a Broader Late Holocene Distribution of the Sandbank Pocketbook (Unionidae: Lampsilis satura Lea 1852) in Texas

Abstract: One way that archaeologists provide unique conservation datasets is through the establishment of pre-Euroamerican baselines for animal communities that were part of human-environment interactions during the last few millennia. Freshwater mussel remains from archaeological sites offer a rich data source for establishing this type of baseline. We establish a conservation baseline for the late Holocene sandbank pocketbook (Lampsilis satura, Lea 1852) in the upper Trinity River of central and north Texas. These data may 1) lead to greater confidence in existing contemporary data for unoinid biogeography; 2) lead to information on whether or not community composition differs between the late Holocene and today; and/or 3) provide a justification for more intensive contemporary surveys. Such data are relatively easily acquired, inexpensive to generate, and highly informative for environmental management.

New Distributional Records for Four Rare Species of Freshwater Mussels (Family: Unionidae) in Southwestern Louisiana

Abstract Recent studies of mussels have documented a gradient of extirpation that extends from Toledo Bend Dam to United States Highway 190 in the lower Sabine River. A similar pattern has been documented for the diversity and abundance of cyprinids. To evaluate whether impacts of the project have extended into nearby tributaries, we assessed the distribution and abundance of threatened species of mussels in Anacoco and Toro bayous, within Vernon and Sabine parishes, respectively. In total, 1,474 live mussels representing 15 species were collected during our survey. Of these, four are considered state-threatened: Fusconaia askewi (Texas pigtoe), Lampsilis satura (sandbank pocketbook), Obovaria jacksoniana (southern hickorynut), and Pleurobema riddellii (Louisiana pigtoe). In general, L. satura, O. jacksoniana, and P. riddellii appear to be rare in Anacoco Bayou and absent from Toro Bayou, whereas F. askewi is more abundant and widely distributed. Effects of backwater related to releases from impoundments, discharge from paper mills, and use of land within the watershed appear to be plausible factors contributing to the constrained distribution of freshwater mussels throughout both bayous. Resumen Estudios recientes de mejillones han documentado un gradiente de extirpación que se extiende desde Toledo Bend Dam hasta la Highway 190 en Estados Unidos en el bajo río Sabine. Un patrón similar ha sido documentado para la diversidad y abundancia de ciprínidos. Para evaluar si los impactos del proyecto se han extendido en las inmediaciones afluentes, evaluamos la distribución y abundancia de especies de mejillones amenazados en los pantanos Anacoco y Toro, dentro de los distritos Vernon y Sabine, respectivamente. Durante nuestro muestreo, se colectaron 1,474 mejillones vivos, representando 15 diferentes especies. De ellas, cuatro son clasificadas como amenazadas por el estado de Texas: Fusconaia askewi, Lampsilis satura, Obovaria jacksoniana, y Pleurobema riddellii. Por lo general, L. satura, O. jacksoniana y P. riddellii parecen ser raras dentro del pantano Anacoco y ausentes dentro del pantano Toro, mientras que F. askewi es más abundante y ampliamente distribuida. Efectos de remanso relacionado a la liberación de agua de embalses, descargo de agua por fábricas de papel, y uso de la tierra dentro de la cuenca parecen ser posibles factores que contribuyen a la limitada distribución de mejillones de agua dulce dentro de los dos pantanos.

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 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.

The Pleurobemini (Bivalvia: Unionida) revisited: Molecular species delineation using a mitochondrial DNA gene reveals multiple conspecifics and undescribed species

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.

Effectiveness of a nonlethal method to quantify gamete production in freshwater mussels

Studies on the reproductive biology of freshwater mussels have contributed to conservation of this group, but methods to study early reproductive stages are either lethal (e.g., histological technique) or useful for only qualitative assessments (e.g., nonlethal syringe technique). Using 2 common mussels (Quadrula apiculata and Quadrula verrucosa) and 2 rare mussels (Quadrula petrina and Quadrula houstonensis) distributed across 3 sites in the Navasota River and San Saba River, Texas, we validated the effectiveness of the syringe technique to quantify gamete production by examining: 1) if estimates of gamete traits (sperm concentration, egg size, and egg concentration) obtained with the syringe technique were correlated to estimates of gamete traits (sperm density, egg size, and egg density) obtained with a histological technique; and 2) if survival, growth, and body condition of individual mussels sampled with the syringe technique were negatively affected in a 2-y mark–recapture field experiment. Pearson’s correlation analysis of gamete production measured over the 1st year of the study indicated sperm concentration and density and egg sizes were correlated between the 2 techniques; however, egg concentration and density were correlated in only some cases. Joint analysis of live and dead encounters from the mark–recapture experiment indicated the syringe technique had little to no effect on survival probability of mussels, and mixed models of shell growth and Fulton’s K body condition index failed to detect sublethal effects of the syringe technique on mussels. The syringe technique is relatively accurate and noninvasive and can be used to study the reproductive biology of threatened and endangered mussels quantitatively. In addition, it can provide the large sample sizes often needed to study the reproductive ecology of mussels.