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The isolated river drainages of eastern North America serve as a natural laboratory to investigate the roles of allopatry and secondary contact in the evolutionary trajectories of recently diverged lineages. Drainage divides facilitate allopatric speciation, but due to their sensitivity to climatic and geomorphological changes, neighboring rivers frequently coalesce, creating recurrent opportunities of isolation and contact throughout the history of aquatic lineages. The freshwater mussel Quadrula quadrula is widely distributed across isolated rivers of eastern North America and possesses high phenotypic and molecular variation across its range. We integrate sequence data from three genomes, including female‐ and male‐inherited mitochondrial markers and thousands of nuclear encoded SNPs with morphology and geography to illuminate the group's divergence history. Across contemporary isolated rivers, we found continuums of molecular and morphological variation, following a pattern of isolation by distance. In contact zones, hybridization was frequent with no apparent fitness consequences, as advanced hybrids were common. Accordingly, we recognize Q. quadrula as a single cohesive species with subspecific variation (Q. quadrula rumphiana). Demographic modeling and divergence dating supported a divergence history characterized by allopatric vicariance followed by secondary contact, likely driven by river rearrangements and Pleistocene glacial cycles. Despite clinal range‐wide variation and hybridization in contact zones, the process‐based species delimitation tool delimitR, which considers demographic scenarios like secondary contact, supported the delimitation of the maximum number of species tested. As such, when interpreting species delimitation results, we suggest careful consideration of spatial sampling and subsequent geographic patterns of biological variation, particularly for wide‐ranging taxa. [ABSTRACT FROM AUTHOR]

Intensive agricultural land use may have adverse impacts on freshwater mussel assemblages.Before European settlement, the Minnesota River Basin (MRB) was home to dense and diverse assemblages of freshwater mussels. Of the 40 species that occurred there, 43% have been extirpated. the St. Croix Basin (SCB) in Minnesota/Wisconsin, in contrast, has maintained a dense and diverse mussel assemblage, probably owing to the maintenance of a higher‐quality ecosystem.Mussels were sampled in four rivers representing an agricultural land‐use gradient. Timed searches were conducted in each of three rivers of the MRB, and in one river in the SCB in 2015. These were previously sampled by the Minnesota Department of Natural Resources (1998–2008).Mussel abundance and richness were lower in the MRB compared with the SCB. There were negligible changes in mussel density in the SCB, whereas abundances declined 17–83% in the MRB over the same period. Rates of decline were greatest for rivers with higher agricultural land use. Individuals of species that inhabited both basins were larger in tributaries with higher agricultural land use.MRB rivers with increased agricultural land use harboured a greater proportion of individuals displaying opportunistic (low life‐span, age and high fecundity) and periodic life‐history traits (moderate to high growth rates, low to intermediate fecundity, life span and age at maturity), whereas SCB assemblages had a greater percentage of mussels displaying equilibrium life‐history traits (long life‐span, late maturity and low reproductive effort). Also, rivers with higher amounts of suspended sediment contained more individuals classified as disturbance tolerant.This study provides evidence that agricultural land use contributes to the loss of mussel diversity and abundance, especially in mussel species that are long lived or slow to reproduce. These life‐history traits may be correlated with increased sensitivity to disturbances commonly observed in agricultural basins, including more and larger flood events. [ABSTRACT FROM AUTHOR]

Freshwater mussels are a diverse group of bivalves with equally diverse life-history traits. We examined host-attracting behaviors, larval-brooding phenology, and larva–host relationships for Ellipsaria lineolata, Leptodea fragilis, Potamilus alatus, and Truncilla truncata through extensive field and laboratory studies. Our data from laboratory trials and recovery and identification of juvenile mussels from naturally infected fish support the long-held assumption that freshwater drum (Aplodinotus grunniens) probably is the exclusive host for these species and is a suitable host for Potamilus ohiensis and Truncilla donaciformis. These species have subtle but distinctive host-attracting behaviors involving use of a mantle lure to facilitate larval transfer to the host. General lure morphology and movement behavior were similar between E. lineolata and T. truncata and between L. fragilis and P. alatus, species pairs that are closely related, whereas displaying orientation was variable among species. Ellipsaria lineolata, L. fragilis, and P. alatus were long-term larval brooders, but duration and correspondence with displaying activity were dissimilar. Truncilla truncata was a short-term larval brooder in the St Croix River and is among the few documented examples of short-term brooding in the Tribe Lampsilini. The range of morphological and behavioral characters in these mussels coupled with the relatively uncommon character of specializing on a single host species make this group a model for evolutionary, phylogenetic, and ecological studies. [ABSTRACT FROM AUTHOR]

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 is transcribed when present in male or female soma. In the present study, we used PCR and RT-PCR to detect the presence and expression of the M mtDNA in male and female somatic and gonadal tissues of the freshwater mussel species Venustaconcha ellipsiformis and Utterbackia peninsularis (Unionidae). This is the first study demonstrating that the M mtDNA is transcribed not only in male gonads, but also in male and female soma in freshwater mussels with DUI. Because of the potentially deleterious nature of heteroplasmy, we suggest the existence of different mechanisms in DUI species to deal with this possibly harmful situation, such as silencing mechanisms for the M mtDNA at the transcriptional, post-transcriptional and/or post-translational levels. These hypotheses will necessitate additional studies in distantly-related DUI species that could possess different mechanisms of action to deal with heteroplasmy. [ABSTRACT FROM AUTHOR]

Managing a rare species can be improved with knowledge of its natural history. The sheepnose (Plethobasus cyphyus) is a freshwater mussel recently listed by the US as federally endangered. We used standard methods to studyP. cyphyusbrooding behaviour, host fishes in the laboratory and under natural conditions, and glochidial morphology. We monitored a population ofP. cyphyusin the Chippewa River, WI during spring and summer 2007–2009 and 2011 and found brooding animals between mid-May and early August. Gravid individuals ranged between 5 and 27 yr (mean age ± 1 s.d. = 13 ± 4 yr).Plethobasus cyphyusbrooded glochidia in outer gills, which varied in colour from red, orange, pink, cream, or white. We observed mature glochidia more commonly in individuals with cream or white gills and these glochidia were released in a clear, adhesive, mucus matrix. In laboratory trials we found several minnow and topminnow species (29 spp.) served as productive suitable native hosts. The mean number of juvenile mussels released per cyprinid per day was significantly higher for trials conducted at 22–25°C compared with those at 18–20°C, and 83% of trials conducted at 18–20°C using suitable host species produced no juveniles. Glochidia had a unique outline and shell morphometrics that distinguishedP. cyphyusfrom seven other Chippewa River mussel species that produce similar sized glochidia. Using morphometrics we determined that mimic shiners (Notropis volucellus) were natural hosts forP. cyphyus, round pigtoe (Pleurobema sintoxia), and Wabash pigtoe (Fusconaia flava). Releasing mucus-bound glochidia has evolved in a variety of mussel species and may be more common than is currently realized. Our data show thatP. cyphyusis a cyprinid host specialist, and propagation efforts for this species can be strengthened through improved access to mature glochidia by using females with cream-coloured gills and increased juvenile production through warmer fish holding temperatures. [ABSTRACT FROM PUBLISHER]

Freshwater mussels are recolonizing the upper Illinois River following their extirpation by pollution in the early part the 20thcentury. From 1990 to 1999, we collected 332 individuals of 18 species between river miles 232.0 and 271.2. Age structure of the community suggests mussels began recolonizing in the early 1980s, which coincides with improvements in water quality and the upper river fish community. We found four sites with five or more species, which we considered to be recently formed mussel beds. We collected live individuals of six species (Actinonaias ligamentina, Alasmidonta marginata, Lampsilis cardium, Lasmigona costata, Pleurobema sintoxia, and Strophitus undulatus) thought to have been extirpated from the entire Illinois River mainstem, and one species (Anodonta suborbiculata) that has recently expanded its range into the upper river. Upper Illinois River tributaries and lower reaches of the Illinois River harbored source populations for the recolonizing mussels. Although the present community does not approximate the pre-disturbance fauna, these data show that given adequate time and improved conditions, mussel communities may recover from a devastating disturbance. [ABSTRACT FROM AUTHOR]

ABSTRACT Hydrodynamic forces and their absence appear to exert differential selection pressure on aquatic biodiversity in lake and stream habitats, creating a tight fit between organismal phenotypes and their environments. Ecophenotypic variants may be the result of genetic differentiation or phenotypic plasticity, where a genotype can produce multiple phenotypes dependent on the environment. Freshwater mussels possess a wide degree of morphological variation that frequently covaries with the environment, making them a good system to understand the mechanisms of ecophenotypic variation across hydrological conditions. We designed a two‐year experiment where individuals from the same Pyganodon grandis maternal brood (half and full siblings) were reared at a controlled site and four natural sites involving one lake and three streams. At the end of the experiment, shell shape was quantified for recaptured (N = 70), wild (N = 206), and zoo‐reared (N = 305) mussels. The maternal individual and 46 recaptured mussels were sequenced for genomic single nucleotide polymorphisms to test for multiple paternity and its effect on offspring morphology. Analysis of covariance found significant differences in shell shape between rearing sites, particularly between stream and lake habitats, but no shape differences were detected across the three stream sites. At two of the four sites, the shell shape of recaptured individuals was not significantly different than that of wild populations. Genomic sequencing and parentage analysis identified 11–27 different fathers among recaptured individuals. Yet no genetic differences were present between stream and lake habitats, and there was no paternal effect on shell shape. Taken together, phenotypic plasticity, over genetic differentiation, is identified as the primary mechanism of ecophenotypic variation. Plasticity is likely ubiquitous across freshwater mussels and may be a key adaptation given their high variance in habitat use. Multiple paternity may also play a role in the evolution of phenotypic plasticity, allowing more males from greater distances opportunities for fertilization, thus increasing genetic connectivity. Lastly, phenotypic plasticity and multiple paternity are convenient properties for freshwater mussel conservation and propagation. Multiple fathers increase the genetic variation of propagated broods, while plasticity may provide resilience to the release of stocked individuals across environmental heterogeneity. [ABSTRACT FROM AUTHOR]

Documents the occurrence of freshwater mussels living on bedrock, a substrate generally considered to be unsuitable. Importance of substrate stability; Significance of the findings.

Abstract: Species boundaries, evolutionary relationships and geographic distributions of many unionoid bivalve species, like those in the genus Pyganodon, remain unresolved in Eastern North America. Because unionoid bivalves are one of the most imperiled groups of animals in the world, understanding the genetic variation within and among populations as well as among species is crucial for effective conservation planning. Conservation of unionoid species is indispensable from a freshwater habitat perspective but also because they possess a unique mitochondrial inheritance system where distinct gender-associated mitochondrial DNA lineages coexist: a female-transmitted (F) mt genome and a male-transmitted (M) mt genome that are involved in the maintenance of separate sexes (=dioecy). In this study, 42 populations of Pyganodon sp. were sampled across a large geographical range and fragments of two mitochondrial genes (cox1 and cox2) were sequenced from both the M- and F-transmitted mtDNA genomes. Our results support the recency of the divergence between P. cataracta and P. fragilis. We also found two relatively divergent F and M lineages within P. grandis. Surprisingly, the relationships among the P. grandis specimens in the F and M sequence trees are not congruent. We found that a single haplotype in P. lacustris has recently swept throughout the M genotype space leading to an unexpectedly low diversity in the M lineage in that species. Our survey put forward some challenging results that force us to rethink hybridization and species boundaries in the genus Pyganodon. As the M and F genomes do not always display the same phylogeographic story in each species, we also discuss the importance of being careful in the interpretation of molecular data based solely on maternal transmitted mtDNA genomes. The involvement of F and M genomes in unionoid bivalve sex determination likely played a role in the genesis of the unorthodox phylogeographic patterns reported herein. [Copyright &y& Elsevier]