Title page for ETD etd-12202010-185148

Type of Document Dissertation
Author Jackson, Nathan Daniel
Author's Email Address njacks4@lsu.edu
URN etd-12202010-185148
Title Evolutionary History of Isolation and Dispersal in North American Ground Skinks (Scincella lateralis)
Degree Doctor of Philosophy (Ph.D.)
Department Biological Sciences
Advisory Committee
Advisor Name Title
Austin, Christopher C. Committee Chair
Brumfield, Robb T. Committee Member
Carstens, Bryan C. Committee Member
Hafner, Mark S. Committee Member
Hellberg, Michael E. Committee Member
Paulsen, Daniel B. Dean's Representative
  • Lower Mississippi River
  • genetic drift
  • incomplete lineage sorting
  • Pleistocene
  • species tree
  • riverine barrier hypothesis
  • channel switching
  • cryptic diversity
  • phylogeography
  • oxbow lake
  • southeastern United States
  • lizard
Date of Defense 2010-12-09
Availability unrestricted
The geographical range, abundance, and cohesion of populations can track landscape and climatic dynamism in ways that help set (and reset) the evolutionary trajectory of a species. Understanding the nature of this interaction can elucidate both evolutionary and geographical history as well as clarify the parameters that govern diversification. In this study, I apply multilocus genetic data from populations of the North American ground skink, Scincella lateralis, to investigate phylogeographic history as well as the interaction between population genetic and geographical processes that have shaped it.

First, I examined the geographic distribution of genetic diversity for S. lateralis and tested whether an interaction between riverine barriers and climate-mediated population contractions have contributed to observed patterns. I found evidence for extensive mtDNA fragmentation resulting in 14 lineages and more moderate fragmentation of nuclear loci resulting in seven populations. The distribution and bounds of diversity are consistent with differentiation in response to riverine barriers that were rendered more isolating in the past when populations likely resided in southern refugia.

I next applied multilocus sequence data and several analytical methods to reconstruct hierarchical relationships among S. lateralis populations and determine how dispersal has impacted divergence. In doing so, I explored the robustness of methods to assumption violations inherent when evaluating natural populations that have diversified recently and without complete isolation. Discordant hierarchical structure was recovered when using different methods and estimates of divergence and migration were invoked to evaluate population relationships. Rejection of a model of isolation-with-migration is largely contingent upon whether regions near adjacent populations are sampled, suggesting that recent gene flow following allopatric isolation is the primary mode of divergence.

Finally, using mtDNA and microsatellite data I investigated the role of rivers in population genetics in more detail by estimating the current rate of S. lateralis migration across the Mississippi River and testing whether migration can be facilitated by meander loop cutoff, a common feature of major rivers. I found that gene flow across the river is high and largely asymmetrical in the direction predicted by cutoff-mediated dispersal, supporting one mechanism that may intermittently contribute to the permeability of riverine barriers.

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