Charles Randklev

Texas A&M University | TAMU · Texas A&M Natural Resources Institute

The conservation of at-risk species is rooted in the ability of natural resource agencies to recognize when a species is imperiled and in need of regulatory action, which can be a difficult task due to incomplete information. Freshwater mussels (Bivalvia: Unionidae), are a highly imperiled group of aquatic organisms and conservation tools such as t...

Unionid mussels deposit growth rings (annuli) within the shell, which can be used to estimate age and growth. Thin-sectioning is a common technique for counting annuli, wherein a cross-section of a shell valve is taken and evaluated by multiple readers. Correctly identifying annuli can be challenging because ambiguous annuli can bias growth estimat...

Life history information such as growth and longevity have been useful for understanding evolutionary relationships and predicting species responses to management and habitat alteration for aquatic species. For unionid mussels, which are globally imperilled, life history information remains unknown for a majority of unionid mussels and because of t...

Corbicula spp. are one of the most prolific aquatic invasive species in the world and can have negative effects on aquatic ecosystems. We performed qualitative field surveys, examined literature accounts and natural history museum holdings, and accessed citizen science data sources to document the distribution of Corbicula in Mexico and shared drai...

Freshwater mussels preserve valuable information about hydrology, climate, and population dynamics, but developing seasonal chronologies can be problematic. Using clumped isotope thermometry, we produced high-resolution reconstructions of modern and historic (~ 1900) temperatures and δ¹⁸Owater from mussel shells collected from an impounded river, t...

Human impacts on aquatic ecosystems have resulted in systemic declines of global freshwater species abundance and richness. Conservation and governmental groups worldwide have designated protected areas to preserve the remaining diversity. The biodiversity hotspot approach, which designates areas based on high levels of species richness, has been u...

Freshwater mussels are globally imperilled, which is attributed to their sensitivity to changes in streamflow and temperature. The Black River in south‐eastern New Mexico, USA, harbours a stronghold population of the federally endangered unionid Popenaias popeii (Texas hornshell). Decreasing discharge and elevated water temperatures are considered...

Accurate taxonomic and distributional information are arguably the most critical components of conservation status assessments but can be greatly affected by misidentifications. The Louisiana pigtoe Pleurobema riddellii is a freshwater mussel proposed as threatened under the US Endangered Species Act. The species belongs to the tribe Pleurobemini,...

Truncilla macrodon¸ the Texas Fawnsfoot, is currently considered to be restricted to the Brazos and Colorado river drainages in central Texas, USA. Subfossil specimens resembling T. macrodon from shell middens in the Trinity river drainage have raised questions about its presumptive range. Extant Truncilla populations occupying the Trinity river dr...

Freshwater mussels are considered the most imperiled group of organisms in North America and systematics research has played an integral role in the development and implementation of their conservation. Despite the importance of systemat-ics in conservation planning, the evolutionary relationships between many mussel taxa remain poorly explored, cl...

Riverine ecosystems are dependent in large part on the climate of the region, and climate change is expected to alter climatic factors of interest, such as precipitation, temperature, and evapotranspiration. In central Texas, precipitation is expected to decrease while temperature increases as the climate changes. Drought and flooding events are al...

Freshwater mussels are particularly sensitive to hydrologic changes, including streamflow and temperature, resulting in global decline. The Devils River in south-central Texas harbors the endangered freshwater mussel Popenaias popeii (Unionidae; Texas hornshell). There is concern that water withdrawals from the underlying aquifer may be negatively...

The Trinity Pigtoe, Fusconaia chunii (Lea, 1862), is a freshwater mussel endemic to the Trinity River drainage in Texas. Here, we report the first population of F. chunii in the San Jacinto River drainage in Texas. We identified three specimens of F. chunii using DNA barcoding, which were morphologically indistinguishable from syntopic Fusconaia fl...

Aim Biogeography seeks to identify and explain the spatial distributions of species and has become an important tool used by conservationists to protect and manage aquatic organisms. Texas, located in the southwestern United States, is home to 52 species of freshwater mussels, 9 of which are endemic to Texas and 7 that are endemic to Texas and neig...

Species distribution models (SDMs) are an increasingly important tool for conservation particularly for difficult-to-study locations and with understudied fauna. Our aims were to (1) use SDMs and ensemble SDMs to predict the distribution of freshwater mussels in the Pánuco River Basin in Central México; (2) determine habitat factors shaping freshwa...

• Overexploitation of freshwater resources coupled with climate change can affect the flow and temperature regimes in rivers, which can be catastrophic for aquatic biota. The San Saba and Llano rivers, located in central Texas, are experiencing low flows and stream dewatering owing to over-allocation. Both systems harbour imperilled species, includ...

• Mussel–flow relationships are not well defined and studies linking behavioural, physiological and life-history traits to hydrological conditions remain scant. This lack of information hinders not only understanding of how flow shapes population and community processes but the development of evidence-based flow recommendations to mitigate mussel d...

Population genomics has significantly increased our ability to make inferences about microevolutionary processes and demographic histories, which have the potential to improve protection and recovery of imperiled species. Freshwater mussels (Bivalvia: Unionida) represent one of the most imperiled groups of organisms globally. Despite systemic decli...

Aim Freshwater 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 freshwat...

1. Translocation is used to conserve mussels, yet there remains a debate about its merit owing to poor understating of its effects on transported mussels. 2. This study evaluated survivorship, body condition, and total glycogen and lipids for one common and widely distributed species (Cyclonaias pustulosa), two rare species (Cyclonaias petrina; Lam...

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 mitc...

Freshwater unionid mussels are among the most imperiled fauna in North America, and their decline has been partially attributed to sediment from anthropogenic activities. However, there remains a debate regarding the role played by sediment in mussel declines due to a lack of field and laboratory evidence. If sediment is responsible for mussel decl...

1. Freshwater ecosystems are experiencing shifts in the natural range and variation of water temperatures due to anthropogenic activity, and these shifts can negatively affect survival, growth, and reproduction of aquatic species. Among the groups most affected are freshwater mussels of the family Unionidae. Knowledge of sublethal and lethal effect...

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 undermin...

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...

• Human impacts on aquatic ecosystems are causing shifts in the composition and distribution of species, leading to subsequent changes in community structure. However, these changes may not be fully realised because of inadequate baseline information. In Texas, such baseline information is generally lacking for cryptic aquatic species such as union...

Information on mussel reproductive life history, age, and growth is important for understanding evolutionary and ecological relationships and predicting how species will respond to conservation and management strategies intended to mitigate threats. In Texas, located within the southwestern United States, 11 species are pending review for listing u...

Spatiotemporal variability in flow determines the physical structures of habitat. During low flows, aquatic organisms can be exposed to reduced dissolved oxygen concentrations, increased water temperature , and desiccation, whereas at high flows, increased velocity and hydraulic forces on the streambed can be equally detrimental. These constraints...

Before this study, researchers had not systematically surveyed the Río Conchos, a tributary of the Rio Grande located in northern Mexico, for freshwater mussels. The Texas hornshell, Popenaias popeii, an endangered species under the United States Endangered Species Act, occurs in the main stem of the Rio Grande near its confluence with the Río Conc...

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 tha...

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 hypoth...

Details for all morphological material examined for morphometric analyses including museum catalog numbers, drainage, and waterbody of collection. Museum abbreviations are as follows: (JBFMC – Joseph Britton Freshwater Mollusk Collection; UF – Florida Museum of Natural History).

Details for all molecular material examined for phylogenetic analyses and additional material examined in the P. ohiensis species complex, including taxon labels, museum catalog numbers, drainage and waterbody of collection, and GenBank accession numbers. Museum abbreviations are as follows: (ASU – Arkansas State University Museum; INHS – Illinois...

Distribution data used to create the conservation map of P. streckersoni sp. nov. Sources of the distribution data were as follows: Baylor University Mayborn Museum (BU-MMC_MO); Fort Worth Museum of Science and History (FWMSH); Texas Parks and Wildlife Department (TPWD), Texas A&M Institute of Renewable Natural Resources (Texas A&M NRI); Joseph Br...

Histograms for CO1 (S3.1) and ND1 (S3.2) illustrating intraspecific and interspecific pairwise uncorrected-p distances for Potamilus amphichaenus and Potamilus streckersoni sp. nov.

Examples of measurements of shell characteristics used for traditional morphometric analysis (S1.1) and shell outline used for Fourier shape morphometrics (S1.2).

Maximum Likelihood (ML) reconstruction generated by IQ-TREE on a concatenated molecular matrix (CO1, ND1, ITS1, 28S). Values above branches represent ultrafast bootstrap support (BS). Strongly supported nodes (i.e., BS ≥ 95) are indicated by asterisks.

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...

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 multisp...

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...

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 develo...

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. Using...

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 specie...

Biplots from principal component analysis (PCA) of traditional morphometrics (A), geometric morphometrics (B), and Fourier morphometrics (C) comparing morphological variation of Lampsilis teres, Yellow Sandshell, between populations from Yegua Creek and the East Fork of the Trinity River. Colors and shapes of points correspond to Yegua Creek (black...

Summary of pros and cons of methods used to diagnose sex of mussels. (DOCX)

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. Using...

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 ani...

The shifting baseline syndrome concept advocates for the use of historical knowledge to inform conservation baselines, but does not address the feasibility of restoring sites to those baselines. In many regions, conservation feasibility varies among sites due to differences in resource availability, statutory power, and land‐owner participation. We...

Human‐mediated threats have led to the rapid decline of species inhabiting freshwater ecosystems, and among the groups most affected are freshwater mussels of the family Unionidae. As a result, species translocation is increasingly used in conservation programmes, yet experimental evidence documenting the success of this strategy is limited. The go...

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 est...

Freshwater mussel (Family: Unionidae) communities in Texas are threatened by impoundment, pollution, and other environmental impacts; understanding their pre-industrial biogeography is critical for ecosystem management. The Louisiana Pigtoe (Pleurobema riddellii), endemic to Louisiana and East Texas, is absent from the Upper Trinity River system bu...

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) a...

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 r...

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...

Zooarchaeological freshwater mussel remains provide information about past environments, faunal communities, and human behaviors. However, one challenge of using archaeological assemblages of animal remains is differential preservation such that bones and shells of some taxa are more vulnerable to processes that destroy or remove them from the reco...

Yegua Creek, a tributary of the Brazos River, Texas has yet to be comprehensively surveyed for freshwater mussels, despite previous studies documenting high mussel abundance and richness and the occurrence of Quadrula houstonensis, a federal candidate species under the U.S. Endangered Species Act. We qualitatively sampled mussels at 52 sites in low...

Ethnobiologists contribute to conservation biology in increasingly meaningful ways. One way that paleoethnobiologists are able to provide a unique conservation dataset is through the establishment of conservation baselines for animal communities that were part of human-environment interactions in during the last few millennia. Freshwater mussel rem...

We assessed the influence of geology, land use, and other features on the occurrence of the rare freshwater mussel smooth pimpleback, Quadrula houstonensis, in the Leon River, Texas. Boosted regression trees were used to assess the relationships between the species' occurrence and potential explanatory variables based on field data from 52 sampling...

The Leon River drainage, located in the Brazos River basin, has not been extensively surveyed for freshwater mussels (Family Unionidae). This is problematic given that three state‐threatened species, Quadrula houstonensis , Quadrula mitchelli , and Truncilla macrodon , have historically occurred in this drainage and two are now candidates for prote...