Date of Award

2004

Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Wildlife Ecology and Wildlife Conservation

Advisor

Judith Rhymer

Second Committee Member

Cynthia S. Loftin

Third Committee Member

Paul Rawson

Abstract

The tidewater mucket (Leptodea ochracea) and yellow lampmussel (Lampsils cariosa) are two freshwater mussel species in serious need of conservation, as they are declining throughout most of their Atlantic slope ranges. Both species are listed as Threatened in Maine, and as Endangered, Threatened, of Special Concern, or Species at Risk in most states and provinces throughout their ranges, which extend from Nova Scotia to Georgia. Because freshwater mussels rely on fish hosts for the movement of their larvae, barriers to the movement of fish hosts, such as habitat fragmentation by dams, may indirectly affect population genetic structure in mussels. An understanding of population genetic structure for L. ochracea and L. cariosa in Maine is important to delineate management units at the state level and may illuminate some of the landscape-level factors affecting population structure in both species. I used microsatellite loci originally developed for Lampsilis abrupta to assess population-level genetic variation for L. cariosa and L. ochracea within and among three river drainages in Maine. Seven of these loci were used to the assess population structure of L. cariosa, but only three of the loci that amplifed in L. ochracea were polymorphic. There was evidence for null alleles at some loci, but consistency in results across loci indicated that my overall findings were robust. Both species had significant genetic differences among populations. Significant differences were observed among populations within and among drainages for L. cariosa. By contrast, within, but not among, drainage differences were observed for L. ochracea. Although L. cariosa exhibited significant isolation by distance, there was no correlation between genetic distance and the number of intervening dams for either species after correcting for the effects of geographic distance. These results will be valuable in developing management plans at the state level, especially in light of impending dam removals, which are likely to require translocations of both species. Where translocations become necessary, I recommend that they occur among least divergent populations, if ecological conditions permit.

Basic taxonomic information has thus far been lacking for L. cariosa and L. ochracea, as morphological characters have proved unreliable in diagnosing monophyletic clades for freshwater mussels. Such information is critical to the development of conservation plans. To address this need, I evaluated range-wide taxonomy for specimens collected throughout the ranges of both species using DNA sequences of the mitochondrial (mtDNA) ND1 gene. L. ochracea and L. cariosa each form well-supported monophyletic lineages. However, individuals from the Potomac River drainage identified as L. cariosa on the basis of morphology had the mtDNA of L. cardium or L. ovata, while individuals identified as L. ovata from the St. Lawrence river drainage had the mtDNA of L. cariosa. The discrepency between morphology and DNA sequence data is evidence for hybridization of L. cariosa with L. cardium and/or L. ovata in the Potomac River drainage, and possibly in the St. Lawrence River drainage. This hybridization could have important implications for the Federal status of L. cariosa, and L. ovata, as well as for the state-level of L. ovata in Vermont, and L. cariosa in Maryland and West Virginia.

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