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Frequent and strong morphological convergence suggests that determinism tends to supersede historical contingencies in evolutionary radiations. For many lineages living within the water column of rivers and streams, hydrodynamic forces drive widespread morphological convergence. Living below the sediment-water interface may release organisms from these hydrodynamic pressures, permitting a broad array of morphologies, and thus less convergence. However, we show here that the semi-infaunal freshwater mussels have environmentally determined convergence in shell morphology. Using 3D morphometric data from 715 individuals among 164 Nearctic species, we find that species occurring in rivers with high flow rates have evolved traits that resist dislodgement from their burrowed position in the streambed: thicker shells for their body size, with the thickest sector of the shell being the most deeply buried. Species occurring in low flow environments have evolved thinner and more uniformly thickened shells, corresponding to an alternative adaptation to dislodgement: increased burrowing efficiency. Within species, individuals also show increased shell thickness for their body size at higher flow rates, suggesting that ecophenotypy may, in part, be an important mechanism for establishing populations in new environments and thus evolutionary divergence in this highly imperiledinvertebrate group., (© The Author(s) 2023. Published by Oxford University Press on behalf of The Society for the Study of Evolution (SSE).)

The United States of America has a diverse collection of freshwater mussels comprising 301 species distributed among 59 genera and two families (Margaritiferidae and Unionidae), each having a unique suite of traits. Mussels are among the most imperilled animals and are critical components of their ecosystems, and successful management, conservation and research requires a cohesive and widely accessible data source. Although trait-based analysis for mussels has increased, only a small proportion of traits reflecting mussel diversity in this region has been collated. Decentralized and non-standardized trait information impedes large-scale analysis. Assembling trait data in a synthetic dataset enables comparison across species and lineages and identification of data gaps. We collated data from the primary literature, books, state and federal reports, theses and dissertations, and museum collections into a centralized dataset covering information on taxonomy, morphology, reproductive ecology and life history, fish hosts, habitats, thermal tolerance, geographic distribution, available genetic information, and conservation status. By collating these traits, we aid researchers in assessing variation in mussel traits and modelling ecosystem change., (© 2023. The Author(s).)

In most animals, mitochondrial DNA is strictly maternally inherited and non-recombining. One exception to this pattern is called doubly uniparental inheritance (DUI), a phenomenon involving the independent transmission of female and male mitochondrial genomes. DUI is known only from the molluskan class Bivalvia. The phylogenetic distribution of male-transmitted mitochondrial DNA (M mtDNA) in bivalves is consistent with several evolutionary scenarios, including multiple independent gains, losses, and varying degrees of recombination with female-transmitted mitochondrial DNA (F mtDNA). In this study, we use phylogenetic methods to test M mtDNA origination hypotheses and infer the prevalence of mitochondrial recombination in bivalves with DUI. Phylogenetic modeling using site concordance factors supported a single origin of M mtDNA in bivalves coupled with recombination acting over long evolutionary timescales. Ongoing mitochondrial recombination is present in Mytilida and Venerida, which results in a pattern of concerted evolution of F mtDNA and M mtDNA. Mitochondrial recombination could be favored to offset the deleterious effects of asexual inheritance and maintain mitonuclear compatibility across tissues. Cardiida and Unionida have gone without recent recombination, possibly due to an extension of the COX2 gene in male mitochondrial DNA. The loss of recombination could be connected to the role of M mtDNA in sex determination or sexual development. Our results support that recombination events may occur throughout the mitochondrial genomes of DUI species. Future investigations may reveal more complex patterns of inheritance of recombinants, which could explain the retention of signal for a single origination of M mtDNA in protein-coding genes., (© The Author(s) 2023. Published by Oxford University Press on behalf of The American Genetic Association. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

The Mekong and Chao Phraya rivers harbor a species-rich freshwater mussel assemblage containing a large radiation of the Pseudodontini species. Members of the genera Bineurus Simpson 1900 and Thaiconcha Bolotov et al., 2020 primarily inhabit small and medium-sized tributaries of these rivers. Here, we present an integrative taxonomic review of these genus-level clades. We show that Bineurus contains four species: B. mouhotii (Lea, 1863), B. exilis (Morelet, 1866) stat. rev., B. anodontinum (Rochebrune, 1882) stat. rev., and B. loeiensis sp. nov. In its turn, Thaiconcha comprises three species: T. callifera (Martens, 1860), T. munelliptica sp. nov., and T. thaiensis sp. nov. Two species, Pseudodon ovalis Morlet, 1889 and P. thomsoni Morlet, 1884, are considered here as questionable taxa. These findings further highlight that Southeast Asia represents a significant evolutionary hotspot of freshwater mussels, which requires further international collaborative research and conservation efforts.

Functional traits are characteristics of an organism that represents how it interacts with its environment and can influence the structure and function of ecosystems. Ecological stoichiometry provides a framework to understand ecosystem structure and function by modeling the coupled flow of elements (e.g. carbon [C], nitrogen [N], phosphorus [P]) between consumers and their environment. Animals tend to be homeostatic in their nutrient requirements and preferentially sequester the element in shortest supply relative to demand, and release relatively more of the element in excess. Tissue stoichiometry is an important functional trait that allows for predictions among the elemental composition of animals, their diet, and their waste products, with important effects on the cycling and availability of nutrients in ecosystems. Here, we examined the tissue stoichiometric niches (C:N:P) and nutrient recycling stoichiometries (N:P) of several filter-feeding freshwater mussels in the subfamily Ambleminae. Despite occupying the same functional-feeding group and being restricted to a single subfamily-level radiation, we found that species occupied distinct stoichiometric niches and that these niches varied, in part, as a function of their evolutionary history. The relationship between phylogenetic divergence and functional divergence suggests that evolutionary processes may be shaping niche complementarity and resource partitioning. Tissue and excretion stoichiometry were negatively correlated as predicted by stoichiometric theory. When scaled to the community, higher species richness and phylogenetic diversity resulted in greater functional evenness and reduced functional dispersion. Filter-feeding bivalves are an ecologically important guild in freshwater ecosystems globally, and our study provides a more nuanced view of the stoichiometric niches and ecological functions performed by this phylogenetically and ecologically diverse assemblage., (© 2020 by the Ecological Society of America.)

The systematics of Oriental freshwater mussels (Bivalvia: Unionidae) is poorly known. Here, we present an integrative revision of the genus Trapezoideus Simpson, 1900 to further understanding of freshwater mussel diversity in the region. We demonstrate that Trapezoideus as currently circumscribed is non-monophyletic, with its former species belonging to six other genera, one of which is new to science and described here. We recognize Trapezoideus as a monotypic genus, comprised of the type species, T. foliaceus. Trapezoideus comptus, T. misellus, T. pallegoixi, and T. peninsularis are transferred to the genus Contradens, T. subclathratus is moved to Indonaia, and T. theca is transferred to Lamellidens. Trapezoideus prashadi is found to be a junior synonym of Arcidopsis footei. Trapezoideus dallianus, T. nesemanni, T. panhai, T. peguensis, and two species new to science are placed in Yaukthwa gen. nov. This genus appears to be endemic of the Western Indochina Subregion. The two new species, Yaukthwa paiensis sp. nov. and Y. inlenensis sp. nov., are both endemic to the Salween River basin. Our results highlight that Southeast Asia is a species-rich freshwater mussel diversity hotspot with numerous local endemic species, which are in need of special conservation efforts.

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.

The freshwater mussel genus Oxynaia Haas, 1911 is thought to be comprised of two geographically disjunct and morphologically variable species groups but the monophyly of this taxon has yet to be tested in any modern cladistic sense. This generic hypothesis has important systematic and biogeographic implications as Oxynaia is the type genus of the currently recognized tribe Oxynaiini (Parreysiinae) and is one of the few genera thought to cross several biogeographically important barriers in Southeast Asia. Morphological and molecular data clearly demonstrate that Oxynaia is not monophyletic, and the type species and its allies (O. jourdyi group) belong to the Unioninae, and more specifically as members of the genus Nodularia Conrad, 1853. Therefore, neither Oxynaia syn. nov. nor Oxynaiini Starobogatov, 1970 are applicable to the Parreysiinae and in the absence of an available name, Indochinella gen. nov. and Indochinellini trib. nov. are described. Several combinations are proposed as follows: Indochinella pugio (Benson, 1862) gen. et comb. nov., Nodularia jourdyi (Morlet, 1886) comb. res., N. gladiator (Ancey, 1881) comb. res., N. diespiter (Mabille, 1887) comb. res. and N. micheloti (Morlet, 1886) comb. res. Finally, we provide an updated freshwater biogeographic division of Southeast Asia.

This data article presents the multi-locus DNA alignments, morphometric data, and details on specimens examined to resolve the evolutionary history of Anodontoides and Strophitus , primarily generic placement and species boundaries. We sequenced 3 loci to create our molecular matrix: cytochrome c oxidase subunit I, NADH dehydrogenase subunit I , and the nuclear-encoded ribosomal internal transcribed spacer I . Aligned sequences were used in phylogenetic analyses and to identify diagnostic nucleotides for Strophitus pascagoulaensis , Strophitus radiatus , Strophitus sp. cf. pascagoulaensis , and Strophitus williamsi. Linear morphometrics (i.e. maximum height, length, and width) were also implemented to further evaluate species boundaries within Strophitus . For further details and experimental findings, please refer to the article published in Molecular Phylogenetics and Evolution (Smith et al., 2018) [1].

Objective: To investigate the increase in oxidative stress during work at moderate altitudes due to additional energy expenditure, tissue anoxia, and UV light exposure., Methods: Thirty US Marine Corps volunteers were divided into placebo (P) and antioxidant supplement (S) groups and tested for markers of oxidative stress before (t0), at the midpoint of (t1), and after (t2) 14 days of winter training at a moderate altitude (approximately 2700 m). The antioxidant supplement consisted of a daily dose of 20,000 IU beta-carotene, 400 IU vitamin E, 500 mg vitamin C, 100 micrograms selenium, and 30 mg zinc. The following markers of oxidative stress were measured: urine thiobarbituric acid reactive substances (TBARSs), urine hydroxynonenal (HNE), urine 8-hydrodeoxyguanosine (8-OHdG), plasma total peroxyl radical trapping potential (TRAP), and plasma lipid hydroperoxides (LPOs). Urine was collected on a 24-hr basis at t0, t1, and t2; blood samples were collected at t0 and t2., Results: P group LPOs increased 30% (p < 0.05) between t0 and t2, whereas S group LPOs did not increase. Both groups exhibited significant increases in urine TBARSs, HNE, and 8-OHdG by t2. Urine TBARSs, HNE, and 8-OHdG increased between t0 and t1 in both groups, with the greater increase in the S group. The conflicting results between the plasma and urine markers of oxidative stress may be due to a time-phase relationship., Conclusions: The results of this study suggest that work in a moderate-altitude cold-weather environment is accompanied by increased oxidative stress, despite relatively high intakes of dietary and supplemental antioxidants.