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Molecular Population Structure and the Biogeographic History of a Regional Fauna: A Case History with Lessons for Conservation Biology
John C. Avise
Vol. 63, No. 1 (Feb., 1992), pp. 62-76
Stable URL: http://www.jstor.org/stable/3545516
Page Count: 15
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Mitochondrial (mt) DNA data on the comparative phylogeographic patterns of 19 species of freshwater, coastal, and marine species in the southeastern U.S.A. are reviewed. Nearly all assayed species exhibit extensive mtDNA polymorphism, although still orders-of-magnitude less than predicted under neutrality theory if evolutionary effective population sizes of females are similar to current census sizes. In both the freshwater and marine realms, deep and geographically concordant forks in intraspecific mtDNA phylogenies commonly distinguish regional populations in the Atlantic versus Gulf Coast areas. These concordant phylogeographic patterns among independently evolving species provide evidence of similar vicariant histories of population separation, and can be related tentatively to episodic changes in environmental conditions during the Pleistocene. However, the heterogeneity of observed genetic distances and inferred separation times are difficult to accommodate under a uniform molecular clock. Additional population genetic structure within geographic regions is evidenced by species-specific shifts in frequencies of more closely related mtDNA haplotypes, and by high frequencies of private haplotypes in some species. The magnitude of local population structure appears partially related to the life history pattern and dispersal capability of a species. The mtDNA results indicate that conspecific populations can be structured at a wide variety of evolutionary depths. The deeper subdivisions in an intraspecific phylogeny reflect the major sources of evolutionary gene pool diversity within a species, while the shallower molecular separations evidence more recent population subdivisions that can be related to comparative dispersal and gene flow patterns. These molecular findings are relevant to the understanding of biogenetic diversity, and carry implications for conservation biology.
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