Search

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]

Venustaconcha ellipsiformis (Unionidae) is a freshwater mussel species inhabiting small to medium streams of the Midwestern United States; however, its occurrence is rather sporadic and populations are often isolated. Due to anthropogenic habitat degradation and water pollution, this species is designated as some sort of conservation status in many states. To prioritize conservation strategies, highly variable genetic markers are necessary to assess population genetic structure and potential genetic erosion of V. ellipsiformis. Using whole genome sequence data, we developed and characterized microsatellite markers for V. ellipsiformis. Among 23 tetranucleotide loci tested, 14 loci were consistently amplified and showed polymorphism. Analyses performed on three populations in the upper Mississippi River basin showed that the number of alleles per locus ranged from 2 to 11 and the observed heterozygosity varied from 0.15 to 0.75. Based on genotypic and allelic rarefaction curves, these loci had adequate statistical power to genetically discriminate between individuals and the sample size was large enough to capture most alleles available in the populations at most loci. Finally, cross-species screening of the loci successfully amplified and showed polymorphism in six species in the tribe Lampsilini. The microsatellite loci developed in this study provide a valuable addition to extant genetic markers for freshwater mussels and can be useful to provide high-level resolution of population genetic parameters for V. ellipsiformis. Such information will be of great value for resource managers developing and prioritizing conservation strategies for imperiled mussel species. [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]

Bivalves exhibit an astonishing diversity of sexual systems and sex-determining mechanisms. They can be gonochoric, hermaphroditic or androgenetic, with both genetic and environmental factors known to determine or influence sex. One unique sex-determining system involving the mitochondrial genome has also been hypothesized to exist in bivalves with doubly uniparental inheritance (DUI) of mtDNA. However, the link between DUI and sex determination remains obscure. In this study, we performed a comparative gonad transcriptomics analysis for two DUI-possessing freshwater mussel species to better understand the mechanisms underlying sex determination and DUI in these bivalves. We used a BLAST reciprocal analysis to identify orthologs between Venustaconcha ellipsiformis and Utterbackia peninsularis and compared our results with previously published sex-specific bivalve transcriptomes to identify conserved sex-determining genes. We also compared our data with other DUI species to identify candidate genes possibly involved in the regulation of DUI. A total of ~12,000 orthologous relationships were found, with 2,583 genes differentially expressed in both species. Among these genes, key sex-determining factors previously reported in vertebrates and in bivalves (e.g., Sry, Dmrt1, Foxl2) were identified, suggesting that some steps of the sex-determination pathway may be deeply conserved in metazoans. Our results also support the hypothesis that a modified ubiquitination mechanism could be responsible for the retention of the paternal mtDNA in male bivalves, and revealed that DNA methylation could also be involved in the regulation of DUI. Globally, our results suggest that sets of genes associated with sex determination and DUI are similar in distantly-related DUI species. [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]

We documented the currently known distribution of the Asian snail Bellamya (=Cipangopaludina) chinensis in Minnesota, along with another viviparid snail, Viviparus georgianus, a North American native whose range has expanded. We also recorded the first known occurrence of Bellamya japonica in Wisconsin. Bellamya chinensis and V. georgianus occurred predominately in lakes within the Minneapolis/St. Paul metropolitan area and the lakes region of northcentral Minnesota. Both species are now established in the three major watersheds that drain Minnesota. We collected Bellamya japonica at six sites in the Namekagon River, part of St. Croix River system in Wisconsin. [ABSTRACT FROM AUTHOR]

The ellipse, Venustaconcha ellipsiformis (Bivalvia: Unionidae), was first recorded in Minnesota from the Straight River in 1987, but we knew little of its distribution in the state, brooding behavior, glochidial host fish relationships or status. To examine these questions, we followed standard procedures to conduct an extensive, qualitative statewide mussel survey, described mantle flapping behavior from field and laboratory observations and identified suitable glochidia hosts in the laboratory and from naturally infested fishes. We found extant populations in five Mississippi River tributaries in southeastern Minnesota: the Cannon, Cedar, Root, Upper Iowa and Zumbro rivers. This appears to be the extent of its historic range in Minnesota as no valid records were found elsewhere. Among these, the largest population occurred in the headwaters of the Root River drainage, which was also the only drainage where we observed recent recruitment.' Brooding V. ellipsiformis quickly flap a small mantle extension, often in response to passing shadows or jarring of the substrate, or their mantle extensions may be slowly undulated. We identified 11 fish species as suitable hosts for ellipsiformis glochidia in the laboratory: brook stickleback (Culaea inconstans), mottled sculpin (Cottus bairdii), slimy sculpin (C. cognatus), logperch (Percina caprodes), mud darter (Etheostoma asprigene), rainbow darter (E. caeruleum), Iowa darter (E. exile), fantail darter (E. flabbelare), Johnny darter (E. nigrum), banded darter (E. zonale) and blackside darter (P. rnaculata). Rainbow darter, fantail darter and blackside darter were also found naturally infested with V. ellipsiformis glochidia. Venustaconcha ellipsiformis should remain classified as a "Threatened" species in Minnesota and management should include conserving populations within drainages due to its restricted range and likely low dispersal ability. [ABSTRACT FROM AUTHOR]

Presents a study which observed predation on zebra mussels by muskrats in two North American rivers and a sequence of events suggesting that muskrats switched prey selection from unionids to zebra mussels. Materials and methods; Results; Discussion.

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]

The ebony shell (Fusconaia ebena) is extirpated from much of the upper Mississippi River drainage. Nonetheless, in the past 25 years 94 live individuals were collected at 23 sites in the upper Mississippi River between Lock and Dam 6 and 26, three sites in the lower St. Croix River, and one site in the lower Wisconsin River. Most of the recent records were from the lower St. Croix River and the lower reaches of the upper Mississippi River. These data support the hypothesis thatLock and Dam 19 inhibits F. ebena from recolonizing the Mississippi River above the dam by preventing its migratory host fish, skipjack herring (Alosa cltrysochloris),from moving upstream. Populations aboveLock and Dam 19 are probably pre-lock and dam remnants that have persisted for over a half century and are at risk of extirpation. Conservation efforts should focus on artificial propagation and dam modifications that allow the passage of migratory fishes. [ABSTRACT FROM AUTHOR]