Graduation Year

2003

Document Type

Thesis

Degree

M.S.

Degree Granting Department

Biology

Major Professor

Karl, Stephen A.

Keywords

biogeography, population genetics, gastropoda, microsatellite dna, mitochondrial dna

Abstract

Melongena corona and closely related congeners are a conspicuous part of the marine intertidal benthic communities of Florida and southeastern Alabama. Significant genetic differentiation among adjacent populations has been conjectured based on variation in shell morphology, habitat discontinuity, low levels of adult motility, and the presence of an aplanic lecithotrophic larval stage. Furthermore, studies of the highly variable shell morphology often have resulted in confusing specific and subspecific definitions of these gastropods, which are often referred to as the "corona complex". Variation in shell morphology may indicate local adaptation or environmentally induced phenotypic plasticity. In this study I utilized mitochondrial DNA sequences in order to reconstruct the phylogenetic relationships of crown conchs, and nuclear microsatellite loci to investigate the patterns of relatedness within and among populations inhabiting the southeastern United States.

Approximately 500 individuals from 20 populations throughout the known range of the Crown Conch were genotyped at eight microsatellite loci. Additionally, a 1200bp portion of the cytochrome oxidase subunit I gene was sequenced along with a 490bp fragment of the 16s ribosomal gene from individuals representing all known species and subspecies of the genus Melongena. Phylogenetic analyses completed with these data provide no support for current taxonomic designations within this group and these genetic data indicate that the corona complex is composed of a single polymorphic species. Furthermore, microsatellite data reveal population structure consistent with restricted gene flow between extant populations and phylogeography heavily influenced by historical sea-level fluctuations during the Late Pleistocene.

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