Publication Date

April 2016


Barry Chernoff


Biology (BIOL)


English (United States)


Little is known about the natural history, biology, and population-genetic structure of Hardhead Silverside, Atherinomorus stipes, a small schooling fish found throughout the Caribbean. Our field observations of A. stipes in Belize and the Florida Keys found that populations tend to be in close association with the shoreline in mangrove or seagrass habitats. Due to this potential island based population structuring, A. stipes presented an interesting opportunity to examine questions about gene flow, isolation by distance, and the number of colonization events at different geographic scales. For this study, the mitochondrial gene nd2 was amplified from 394 individuals collected from seven different Belizean cays (N=175) and from eight different Floridian keys (N=219). Results show surprisingly high haplotype diversity both within and between island groups, as well as a high prevalence of unique haplotypes within each island population. Interestingly, the island populations also exhibit similar genetic structures: high levels of heterogeneity and no correlation between geographic distance and genetic differentiation. Genetic divergence suggests that the Belizean and Floridian groups have little to no gene flow between them. Haplotypes within each island group form well-supported monophyletic clades with a divergence of 4.5%, which indicates possible speciation. Paradoxically, we observed four highly differentiated from Florida that had Belizean-type haplotypes. Statistical analyses of each island group indicate that they are evolving under different models of evolution, suggesting that they are under differing selection pressures. This thesis constitutes the first genetic analysis of Atherinomorus stipes.

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