Exploring levels of genetic variation in the freshwater mussel genus Villosa (Bivalvia Unionidae) at different spatial and systematic scales: Implications for biogeography, taxonomy, and conservation.

摘要

Freshwater mussels (Family Unionidae) are one of the most imperiled groups of animals in North America with approximately 75% of the currently recognized species listed by federal or states as endangered, threatened or species of concern. Despite this designation, conservation of freshwater mussels has been extremely difficult being limited by an inadequate knowledge of even the most basic principles of biology (e.g. life history, reproductive biology, ecology, habitat requirements, etc). Two of these that continue to pose challenges to the conservation of this important group of animals include; identification of (1) taxonomic units appropriate for conservation, and (2) criteria useful for the establishment or re-establishment of populations of freshwater mussels that are endangered, threatened, or species of concern. To address issues associated with the identification of freshwater mussels we employed a modern phylogenetic approach using an enigmatic and important group of unionids (Villosa) in order to assess ambiguities in taxonomic position and delineate species boundaries. We used nucleotide sequences of the cytochrome oxidase I subunit (COI) and NADH dehydrogenase I (NDI) subunit of the mitochondrial DNA (mtDNA) genome to infer taxonomic boundaries and to provide a more relevant phylogenetic framework within the Unionidae. We also used a nearly panmictic species, Villosa iris, to address patterns of speciation associated with observed morphological variation in a small river taxon which also allowed us to evaluate existing hypotheses regarding the evolution of drainage basins of the eastern U.S. Lastly, we provide a set of criteria that should be addressed for conservation activities associated with the relocation, translocation, and reintroduction of freshwater mussels.;Our assessment of Villosa iris revealed multiple cryptic species across the range of this taxon that correlate with vicariant events associated with the evolution of major drainages throughout the eastern U.S. (Chapter 2). Our phylogenetic studies also revealed a polyphyletic Villosa comprised of at least 9 clades that include species from five different genera (Chapter 3). These studies indicate (1) that current systematics for Villosa is largely inadequate, (2) morphological (conchological) characters used to diagnose taxonomic boundaries within the Villosa in most instances are not useful, (3) a modern phylogenetic approach is necessary for accurate identification of evolutionary lineages within unionids, (4) modern phylogenetic methods will aid in implementing appropriate conservation strategies.;Finally, using two federally endangered freshwater mussels, Pleurobema clava and Epioblasma torulosa rangiana; we provide a framework for evaluating potential sites for relocation, translocation, and reintroduction in two Ohio watersheds. This framework includes a discussion of past and current threats, conservation activities, and identifies biological and physical criteria that can be used to evaluate potential sites for conservation activities.