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Abstract
Water movement, the primary seed dispersal agent for many aquatic plants, is unidirectionalthroughout an upland drainage basin; thus, models of gene flow based on terrestrial environments, whereseed dispersal is often multidirectional, may be inadequate for representing patterns of gene flow inaquatic plants. Few studies, however, have investigated the influence of stream flow on patterns ofgenetic variation in aquatic plants; and these studies have reported contradictory results. Furthermore,gene flow both within and among populations has rarely been examined in stream environments, andmany questions remain concerning how these processes function at different scales of analysis. Thisproject uses molecular techniques to examine gene flow in Hymenocallis coronaria, commonly known asthe Shoals spider-lily, an aquatic plant that occurs in shoal habitats in streams from Alabama to SouthCarolina, but is absent from several watersheds in the middle of its range. The first broad objective is toexamine the effects of stream flow on genetic diversity and gene flow patterns within and amongpopulations of Hymenocallis coronaria. Specifically, nuclear DNA markers are used to: 1) determinewhether genetic variability increases progressively downstream both within and among populations, 2)test the one-dimensional stepping stone and metapopulation models, and 3) examine whether thesepatterns are consistent both within and among populations. The second broad objective is to examine theeffects of shoal habitat characteristics and hydroelectric dam operation on population size anddistribution, and genetic structure, and, in turn, how these factors affect microevolutionary processes in anaquatic macrophyte. Nuclear and chloroplast DNA molecular analysis and habitat specific data are usediito: 1) determine whether hydroelectric power generation or stream geomorphic characteristics havesignificant effects on H. coronaria population size and distribution, 2) establish whether the geneticstructure has any relationship to the distribution gap located in the middle of the species range, and 3)conclude which spatial scales and locations should be targeted for conservation of this species.