Doctoral Dissertation Research: Multi-Scale Analysis of Gene Flow in the Emergent Aquatic Macrophyte Hymenocallis coronaria

University Of Georgia Research Foundation Inc, Athens GA

Investigators

Abstract

Water movement, which is the primary seed dispersal agent for many aquatic plants, is unidirectional throughout an upland drainage basin. Models of gene flow based on terrestrial environments, where seed dispersal is often multidirectional, are likely inadequate for representing patterns of gene flow in aquatic plants. Few studies have investigated the influence of unidirectional stream flow on patterns of genetic variation in aquatic plants, however, 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 Doctoral Dissertation Research Improvement project will use molecular techniques to examine gene flow in Hymenocallis coronaria (shoals spider lily), an aquatic plant that occurs in shoal habitats in piedmont streams from Alabama to South Carolina but is absent from several watersheds in the middle of its range. The project's first broad objective is to examine the effects of unidirectional stream flow on genetic structure and gene flow within and among populations of Hymenocallis coronaria. Specifically, a combination of nuclear DNA and chloroplast DNA markers will be used to (1) determine whether genetic variability increases progressively downstream both within and among populations, (2) examine the influence of pollen flow vs. seed flow in stream environments, and (3) test which of three gene flow models best represents the patterns of gene flow among populations. The second broad objective is to examine the effects of habitat characteristics and land-use history on population distribution, genetic structure, and gene flow, and how these factors, in turn, affect microevolutionary processes in an aquatic macrophyte. In concert with molecular techniques, stream discharge, water temperature, turbidity, dissolved oxygen, sediment depth in the channel, shoals lithology, and strike and dip of the shoals rock units will be measured to determine (1) which factors are associated with the absence of Hymenocallis coronaria populations from the middle of the species range, (2) whether the exclusion of populations from the uninhabited drainage basins is of prehistoric origin or result from more recent human-related disturbance, and (3) whether populations in isolated drainages are at a greater risk for extinction with ongoing land-use changes. Hymenocallis coronaria is a rare plant that has a relatively restricted range in the southeastern United States. The plant is protected as a threatened or endangered species by the states of Alabama and Georgia. It is listed as imperiled by the state of South Carolina; and protection has been sought under the Endangered Species Act. Documented population extinctions have occurred due to reservoir impoundment, and populations continue to be threatened by further water resource development. In addition to providing information about gene flow in aquatic environments, this research will further basic understanding of the response of this relatively rare species to changing environmental conditions within its range. The results also will inform resource managers as they formulate policy that affects not only this particular state-level endangered botanical resource but potentially other aquatic plants throughout the region affected by the same set of disturbances. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.