A primary goal of population genetics is to identify the role of
microevolutionary forces in producing observed patterns of molecular and phenotypic
variation. I conducted four studies in the northern leopard frog, Rana pipiens, to
determine just how mutation, migration, genetic drift, and selection influenced,
genetic structure of mitochondrial DNA (mtDNA), nuclear DNA, and a single locus
polymorphism that determines dorsal coloration. In the first study, I surveyed the
literature concerning color and pattern polymorphisms in anurans. I conclude that
anuran polymorphisms remain a rich but largely unexploited system for studying the
evolution of phenotypic variation in nature.
In the second study, I compared mitochondrial DNA variation from 35
populations distributed across the species' range. A phylogenetic analysis indicated R.
pipiens is split into two deeply divergent mtDNA groups, a western group and an
eastern group. Phylogeographic and demographic analyses indicated that although
restricted gene flow with isolation by distance explained the majority of the processes
influencing current genetic structure, population bottlenecks and expansions also
played an important role.
In the third study, I investigated mtDNA and microsatellite variation in Pacific
Northwest populations of R. pipiens, where a recent range contraction had occurred.
I found that peripheral populations had reduced levels of genetic variation compared to
more interior populations. Moreover, I found that historic samples from peripheral
population already had reduced levels of genetic variation. Therefore, low diversity in
the remnant populations could not be ascribed to the recent range contraction.
In the fourth study, I compared genetic structure from a suite of putatively
neutral molecular markers with that derived from the color polymorphism locus.
Genetic structure at the color locus, assessed both spatially and temporally, was
indistinguishable from structure at neutral loci. This study exemplifies the importance
of investigating for evidence of selective maintenance before studies attempt to
measure the selective mechanisms maintaining a polymorphism.
Overall, my research helps to elucidate how biogeographic and
microevolutionary forces influence a wide-spread North American species, R. pipiens. / Graduation date: 2004
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/29637 |
| Date | 09 June 2003 |
| Creators | Hoffman, Eric Adam |
| Contributors | Blouin, Michael S. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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