Theses and Dissertations

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Defense Date

2003

Document Type

Thesis - NSU Access Only

Degree Name

M.S. Marine Biology

Department

Oceanographic Center

First Advisor

Mahmood Shivji

Second Advisor

Charles G. Messing

Third Advisor

Andrew Rogerson

Abstract

Chapter 1:

The great white shark, Carcharodon carcharias, is the most widely protected elasmobranch in the world, and is classified as Vulnerable by the IUCN and listed on Appendix III of CITES. Monitoring of trade in white shark products and enforcement of harvest and trade prohibitions is problematic, however, in large part due to difficulties in identifying marketed shark parts (e.g., dried fins, meat and processed carcasses) to species level. To address these conservation and management problems, I have developed a rapid, molecular diagnostic assay based on species-specific PCR primer design for accurate identification of white shark body parts. The assay is novel in several respects: It employs a multiplex PCR assay utilizing both nuclear (ribosomal internal transcribed spacer 2) and mitochondrial (cytochrome b) loci simultaneously to achieve a highly robust measure of diagnostic accuracy; it is very sensitive, detecting the presence of white shark DNA in a mixture of genomic DNAs from up to ten different commercially fished shark species pooled together in a single PCR tube; and it successfully identifies white shark DNA from globally distributed animals. In addition to its utility for white shark trade monitoring and conservation applications, this highly streamlined, bi-organelle, multiplex PCR assay may prove useful as a general model for the design of genetic assays aimed at detecting body parts from other protected and threatened species.

Chapter 2:

Sharks and their relatives (Class Chondrichthyes) were the among the first vertebrates to evolve internal fertilization, yet our understanding of mating and parentage in this ancient group lags far behind many other animal groups. This is especially surprising because many shark populations worldwide are experiencing severe declines in abundance, and conservation planners are in dire need of basic information on their reproductive natural history. Based on a few genetic and field observational studies, current speculation is that polyandrous mating and multiple paternity may be as common in sharks as they are in most other vertebrate groups. Here, I examine this idea by genetically analyzing paternity in the hammerhead, Sphyrna tiburo (bonnethead), from the west coast of Florida, using the largest and most geographically widespread sample of shark litters analyzed to date. Contrary to expectations based on results from a few other shark species, the ability of female bonnetheads to store sperm and observations of their social behavior, I found that over 80% of females produced litters sired by a single male (genetic monogamy). This is the first record of this genetic mating system in this ancient class of fishes. When multiple paternity does occur in S. tiburo, I found no evidence for the involvement of any more than one additional male, no consistent pattern of paternity skew between fathers and an overrepresentation of multiple paternity in bigger litters with larger mothers. My results suggest that sharks and their relatives may exhibit diverse mating strategies and, as a result, some species may have a reduced capacity to maintain genetic variation in the face of large-scale depletion or changes in sex-ratio.

Comments

Funding from Graduate Research Fellowship, NSF.

Further funding from the Roe Foundation, the Wildlife Conservation Society, the David and Lucile Packard Foundation, the Hai Stiftung Foundation, the Curtis and Edith Munson Foundation.

Additional funding from the Florida Sea Grant Program (R/LR-B-54).

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