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The larvae of freshwater mussels in the order Unionoida are obligate parasites on fishes. Because adult mussels are infaunal and largely sessile, it is generally assumed that the majority of gene flow among mussel populations relies on the dispersal of larvae by their hosts. The objective of this study was to compare the genetic diversity and the degree of congruence between the population structures of two related freshwater mussels Leptodea leptodon and Leptodea fragilis and their fish host, Aplodinotus grunniens. Host specificity in parasites has been shown to result in greater congruence between the population structures of the two interacting species, and assessing the congruence of genetic structure of the endangered L. leptodon with its sister species L. fragilis and their sole host is an important step in understanding the impact of host dispersal on population structure. Analysis of microsatellite data indicated that despite its imperiled status, L. leptodon displayed greater genetic diversity than the more common L. fragilis. However, the population structures of all three species were incongruent even in the presence of substantial gene flow. Other factors such as habitat specificity may play a role in generating the differences in population structure observed. This study indicates that barriers to gene flow or lack of available host fish are not the cause of decline of the federally endangered L. leptodon, and suggests that alternative explanations should be considered. [ABSTRACT FROM AUTHOR]

Freshwater molluscs are globally critically threatened, yet little is known about their genetic diversity. We describe the isolation and characterization of the first microsatellite markers for the European swan mussel, Anodonta cygnea. Nine loci were polymorphic in a panel of 110 individuals from seven German and Estonian populations. Number of alleles ranged from 2 to 14 and heterozygosity levels ranged from 0.021 to 0.498 for Ho and from 0.069 to 0.634 for He. Deficiency of heterozygous genotypes was observed in six loci. The length of the microsatellite repeat motives was positively correlated with the allele numbers in the respective loci. [ABSTRACT FROM AUTHOR]

Over 70% of North American freshwater mussel species (families Unionidae and Margaritiferidae) are listed as threatened or endangered. Knowledge of the genetic structure of target species is essential for the development of effective conservation plans. Because Ambelma plicata is a common species, its population genetic structure is likely to be relatively intact, making it a logical model species for investigations of freshwater mussel population genetics. Using mtDNA and allozymes, we determined the genotypes of 170+ individuals in each of three distinct drainages: Lake Erie, Ohio River, and the Lower Mississippi River. Overall, within-population variation increased significantly from north to south, with unique haplotypes and allele frequencies in the Kiamichi River (Lower Mississippi River drainage). Genetic diversity was relatively low in the Strawberry River (Lower Mississippi River drainage), and in the Lake Erie drainage. We calculated significant among-population structure using both molecular markers (A.p. Φst = 0.15, θst = 0.12). Using a hierarchical approach, we found low genetic structure among rivers and drainages separated by large geographic distances, indicating high effective population size and/or highly vagile fish hosts for this species. Genetic structure in the Lake Erie drainage was similar to that in the Ohio River, and indicates that northern populations were founded from at least two glacial refugia following the Pleistocene. Conservation of genetic diversity in Amblemaplicata and other mussel species with similar genetic structure should focus on protection of a number of individual populations, especially those in southern rivers. [ABSTRACT FROM AUTHOR]