Date of Award

12-2025

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

School

Biological, Environmental, and Earth Sciences

Committee Chair

Dr. Nicole Phillips

Committee Chair School

Biological, Environmental, and Earth Sciences

Committee Member 2

Dr. Kevin Feldheim

Committee Member 3

Dr. Brian Kreiser

Committee Member 3 School

Biological, Environmental, and Earth Sciences

Committee Member 4

Dr. Peter Kyne

Committee Member 5

Dr. Alec Moore

Abstract

The Critically Endangered Largetooth Sawfish Pristis pristis is a large coastal ray that has undergone severe declines in range and abundance over the last century, yet the genetic consequences of these declines remain unclear due to limited baseline genetic data. Dried rostra specimens from natural history collections were used to obtain historical DNA dating back to the 19th century. A standardized framework was developed and applied to filter specimens prior to their inclusion in analyses based on confidence in their collection metadata, increasing reliability in results. Historical genetic data from mitochondrial and nuclear markers were compared to contemporary datasets to assess genetic diversity loss. Microsatellites were also used to evaluate the ability to assign specimens of unknown origin to a putative region of origin, demonstrating the utility of specimens as reference datasets for population assignment testing. Historical genetic diversity was found to be moderate to high relative to other sharks and rays. Both mitochondrial and microsatellite data revealed strong differentiation between global regions, supporting two distinct lineages, Eastern Pacific/Atlantic and Indo-West Pacific. Mitochondrial data indicated fine-scale structure consistent with female philopatry, while microsatellites suggested broader male-mediated gene flow within regions, including between Australia and Papua New Guinea. Genetic losses accompanied range contractions, with unique genetic diversity lost following local extinctions. In Australia, genetic diversity remained stable, whereas in Brazil genetic loss was detected in mitochondrial but not microsatellite data. These findings demonstrate the importance of specimens for studying biodiversity loss and emphasize the need for international collaboration between Australia and Papua New Guinea, better enforcement of protections in Brazil, and identifying a stronghold population Eastern Pacific/Atlantic for safeguarding P. pristis into the future.

ORCID ID

https://orcid.org/0009-0007-2387-7197

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