Local-Scale Landscape Genetics of the Salt Marsh Snail Melampus bidentatus
Local-Scale Landscape Genetics of the Salt Marsh Snail Melampus bidentatus <ul><li>Jesyka Meléndez ¹ & John P. Wares ² </li></ul><ul><li>¹Undergraduate research student from University of P.R. in Cayey, Department of Biology. </li></ul><ul><li>² Mentor in charge of investigation. PhD professor at the University of Georgia, Athens, Department of Genetics. </li></ul><ul><li>SUNFIG Genetics Program, Summer Internship 2009 </li></ul><ul><li>RISE Program 5 R25 GM059429 </li></ul>Much research over the past few decades has gone into studying patterns of genetic diversity in natural populations. One of the many applications of this data has been the evaluation of how genetic diversity is distributed across the spatial distribution of a species. Genetic diversity is not spatially uniform and can be classified into one of three systems; open, closed or neutral . We hypothesized that islands that were located downstream in the marsh habitat, were large, and were geologically older, would present the largest amount of diversity. When determining a model to explain genetic diversity patterns, whether it is distributed randomly (neutral system), by contemporary (open system) or historical (closed system) processes, we need to evaluate the distribution of diversity across the landscape of interest. Contrasts must be made among populations of different areas taking into consideration size and age of habitat; habitat differences; larval recruitment differences. <ul><li>Why this study is important: </li></ul><ul><ul><li>Genetic diversity within a species is one of the most important factors that allows for survival of the species. It permits adaptation. </li></ul></ul><ul><ul><li>Evaluating patterns of genetic diversity, and the mechanisms that maintain these patterns, can provide insight into why we see patterns in other levels. </li></ul></ul>M. bidentatus was used as the model organism. Using collected individuals from populations at different sites in the Georgia coast, we studied diversity patterns in the sequences of extracted mitochondrial DNA (the cytochrome oxidase I, or COI, gene region), and identified the genetic differences within and between populations. Figure 2 . The bubble chart above presents the correlation between hammock size, age and diversity. The larger the bubble, the larger π was in a given population. Figure 3 . The Box plot below presents the genetic divergence between old and young islands, where 1 indicates young and 2 old. It is clear that they are very different, old islands being much more diverse. Figure 1 . Above, a map of the Georgia Coastal Ecosystems. All of our locations for population collection were centered along Sapelo island. Note: Not all the locations indicated in the map were included in the study. Analysis of variance (ANOVA) of π (estimate of nucleotide diversity) with island size and age suggested a strong (p<0.031) difference of diversity between islands/hammocks of <1Ha and those that are larger (Fig. 3). There was no significant effect of habitat age (see Fig. 1); habitat age and size are weakly correlated (r=0.31, n.s.; Fig. 2). This result suggests classic metapopulation dynamics, with small populations subject to increased extinction and recolonization.