Theses and Dissertations

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Defense Date

2005

Document Type

Thesis - NSU Access Only

Department

Oceanographic Center

First Advisor

Mahmood Shivji

Second Advisor

James D. Thomas

Third Advisor

Charles G. Messing

Abstract

Chapter 1

Effective spatial management of coral reefs including design of marine protected areas requires an understanding of inter-population genetic connectivity. We report a comparative analysis of gene flow among three commensal invertebrates occupying the same host sponge (Callyspongia vaginalis) but displaying contrasting reproductive dispersal strategies: the broadcast spawning brittle star Ophiothrix lineata and two brooding amphipods Leucothoe kensleyi and Leucothoe ashleyae. Sequence variation in the mitochondrial COI gene was used to infer connectivity along 355km of the Florida reef system and between Florida and Belize. O. lineata showed significant genetic structuring between Florida and Belize, and a pattern of isolation by distance but no significant genetic structuring along the Florida coastline. Both amphipods despite direct development also showed high gene flow along the Florida coastline. A nested clade analysis on the L. kensleyi data identified two major processes operating at different temporal scales. Inference of restricted gene flow due to isolation by distance dominated younger clades, whereas the inference for older clades was long distance dispersal from northern populations south into the Florida Keys. Multiple inferences of long distance dispersal support the hypothesis that rafting in detached sponges is the likely mechanism responsible for the high levels of overall gene flow detected by AMOVA along the Florida reef system. However, rafting appears to be less likely across deep open water, as connectivity between Florida and Belize (1072km) is highly restricted. Our results show that making assumptions about connectivity based simply on reproductive strategy may be misleading, and highlight the need for examining coral reef connectivity across diverse taxa.

Chapter 2

Although over half of all known elasmobranchs are batoids, with many species exploited and several of conservation concern, little is known of their population genetic structure and intraspecific evolutionary history. Here I investigate gene flow among geographic populations of the southern stingray (Dasyatis americana), a large, recreationally important, demersal batoid that ranges from New Jersey, USA and the northern Gulf of Mexico to southern Brazil. Sequence variation in 648 bp of the mitochondrial control region was used to infer patterns of gene flow among North American and Caribbean populations. Analysis of 267 individuals from eight regions identified 67 distinct haplotypes and AMOVA results revealed high levels of population structure (overall φST = 0.50, P < 0.001) highlighting that populations need to be managed as distinct evolutionary units. The highly structured nature of D. americana populations was clearly evident in a nested clade analysis (NCA), which detected restricted gene flow at three levels of nesting. In addition, numerous range expansions, dispersals, and colonizations were detected and their path through the Caribbean identified a major phylogeographic break at the Florida Channel.

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