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The Host-Habitat Continuum Concept (HHCC) predicts changes in the proportions of freshwater mussels with different life-history strategies (i.e., equilibrium, periodic, opportunistic) along stream gradients and between habitat types. We analyzed mussel assemblages from a large, diverse geographic area to test predictions of the HHCC and to assess if species richness, abundance, and host strategy patterns change predictably among different habitats (lakes, reservoirs, and streams) and stream sizes. Species richness and abundance were low in lakes, reservoirs, and small streams and increased with stream size. Mussels use various strategies to attract fish hosts and the proportion of mussels that release conglutinates (i.e., packets of glochida) increased with stream size and the proportion that use lures decreased. Our results supported predictions of the HHCC: greater proportions of opportunistic or periodic strategists in lakes, reservoirs, and small streams and a shift to equilibrium strategists in larger streams. Patterns differed slightly in lakes and reservoirs with a higher proportion of periodic strategists than expected. Not all watersheds followed predictions of the HHCC likely due to the effects of biogeography and anthropogenic impacts. These life history strategy patterns can be used to test the expected composition of mussel communities and to detect possible anthropogenic impacts. [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]