Multi-scale analysis of gene flow in the emergent aquatic macrophyte Hymenocallis coronaria
Markwith, Scott Howard
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Water movement, the primary seed dispersal agent for many aquatic plants, is unidirectional throughout an upland drainage basin; thus, models of gene flow based on terrestrial environments, where seed dispersal is often multidirectional, may be inadequate for representing patterns of gene flow in aquatic plants. Few studies, however, have investigated the influence of stream flow on patterns of genetic 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, and many questions remain concerning how these processes function at different scales of analysis. This project uses molecular techniques to examine gene flow in Hymenocallis coronaria, commonly known as the Shoals spider-lily, an aquatic plant that occurs in shoal habitats in streams from Alabama to South Carolina, but is absent from several watersheds in the middle of its range. The first broad objective is to examine the effects of stream flow on genetic diversity and gene flow patterns within and among populations of Hymenocallis coronaria. Specifically, nuclear DNA markers are used to: 1) determine whether genetic variability increases progressively downstream both within and among populations, 2) test the one-dimensional stepping stone and metapopulation models, and 3) examine whether these patterns are consistent both within and among populations. The second broad objective is to examine the effects of shoal habitat characteristics and hydroelectric dam operation on population size and distribution, and genetic structure, and, in turn, how these factors affect microevolutionary processes in an aquatic macrophyte. Nuclear and chloroplast DNA molecular analysis and habitat specific data are used ii to: 1) determine whether hydroelectric power generation or stream geomorphic characteristics have significant effects on H. coronaria population size and distribution, 2) establish whether the genetic structure 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.