Date of Award
5-2010
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Legacy Department
Biological Sciences
Committee Chair/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.
Recommended Citation
Nance, Holly, "The Population Genetics of the Endangered Scalloped Hammerhead Shark, Sphyrna lewini, Across its Eastern Pacific Range" (2010). All Dissertations. 522.
https://open.clemson.edu/all_dissertations/522