Date of Award

5-2010

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Biological Sciences

Advisor

Marko, Peter B

Committee Member

Ptacek , Margaret

Committee Member

Lawton-Rauh , Amy

Committee Member

Tonkyn , David

Committee Member

Klimley , Pete

Abstract

I have characterized the population genetic structure, inferred the evolutionary processes shaping it, and estimated effective population size (Ne) using different contemporary and coalescent methods in the endangered scalloped hammerhead shark, Sphyrna lewini, throughout its Eastern Pacific (EP) range. I found significant genetic differentiation among seven coastal sites between Mexico and Ecuador using 15 microsatellite loci, and significant isolation by distance among samples of mtDNA control region haplotypes. While Bayesian statistical analyses and coalescent-based methods revealed low levels of ecological connectivity between most sampled sites (point estimates of Nm = 0.6 - 7.3), mismatch analyses showed that all populations experienced a relatively ancient expansion roughly 220,000 years ago (suggesting a common demographic history). Following this ancient expansion, EP S. lewini experienced steep declines in genetic diversity (Θ = 4Neμ) and populations diverged within the last several centuries. Both decline and divergence happened concurrently, as 90% posterior probability densities of time since divergence overlap with those of time since decline. This overlap suggests a causal relationship between the two and both may be responsible for the genetic structure evident throughout the EP today. Population decline likely resulted in fewer migrants and lower ecological connectivity. Smaller, isolated populations then experienced a greater magnitude of genetic drift, ultimately driving their rapid diversification throughout the EP. The recent timing of these events and their overlap with historical fishing practices throughout this region highlight the evolutionary impact that overfishing can have on natural populations.

Included in

Genetics Commons

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