Publication Date

8-1-2000

Degree Program

Department of Biology

Degree Type

Master of Science

Abstract

Spiraea virginiana Britton is a rare federally listed rhizomatous shrub endemic to the southern Blue Ridge and Appalachian Plateau physiographic provinces. Populations of S. virginiana are found restricted to scoured sections of high gradient streams within the Ohio River drainage. Present evidence indicates the species is reproducing asexually, most probably through the deposition of rhizomes from upstream populations forming new downstream ramets. Phenotypic variation was examined through a morphometric evaluation of 25 leaf measurements and analyzed using Principal Components Analysis (PCA) and discriminant function analysis. Identity and structure at the molecular level as examined with Randomly Amplified Polymorphic DNA (RAPDs) and band patterns were used to construct a cluster analysis. Past gene flow was identified by combining cluster analysis and biogeography data. Results support the current species delineation by affirming the S. virginiana/S. corymbosa species boundary. Patterns of variation found within S. virginiana indicate that there is some degree of relatedness along short reaches of a single river and that within a secondary drainage basin a downstream distribution of propagules from multiple tributaries results in a mix of phenotypes. Patterns of variation further indicate that past gene flow had occurred across drainages suggesting a pattern of migration during Pleistocene glaciation. Results place the S. virginiana ancestral population in the southern part of its range suggesting a southward migration followed by recolinization northward, concordant with the work of Delcourt and Delcourt (1981, 1984). Biogeographical patterns of variation within S. virginiana identify the Cumberland Plateau as a migratory route. In addition, evidence suggests that the deeply dissected Cumberland Plateau is the probable site of a Pleistocene refugium.

Disciplines

Medical Sciences | Plant Sciences

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