Systematics Section / ASPT
Knaus, Brian , Cronn, RC , Liston, Aaron .
The Architecture of Infraspecific Differentiation: A Case Study in Astragalus lentiginosus (Fabaceae).
Infraspecific taxa have been considered groups of organisms in the early stages of speciation at least since Darwin. Application of infraspecific ranks have been controversial due to uncertainty in whether these taxa represent biologically cohesive groups or represent ‘minor’ novelties. We posit that infraspecific taxa are important units of evolutionary potential using the extremely polymorphic species Astragalus lentiginosus (Fabaceae) as an example. We compare a morphometric dataset of herbarium specimens to a dataset simulated from ranges provided in the most recent comprehensive monograph of the species as well as climatic data extracted from the PRISM dataset. Taxonomically important characters display a dramatic range (e.g., floral axis in fruit ranges from less than one cm to over 15 cm), significant clinality in univariate and multivatiate analyses, and correlation to climatic parameters. However, clustering methods result in similarly probable groups regardless of group number. This suggests that different systems of infraspecific taxonomy are equally significant. Clinality in A. lentiginosus has been obfuscated through patchiness in distribution and heterogeneity of habitat in the American Intermountain West, such that any single transect may not capture the cline but a range-wide perspective is required to assemble all of the pieces. Unlike steep clines, considered as evidence that taxa may have begun to evolve barriers to reproduction, the cline in A. lentiginosus is broad and encompasses most of the American West. Current and historic taxonomy are evidence as to how extinction of intermediates may create distinctiveness among the remaining taxa. We conclude that clinal speciation has played an important role in the evolution of one of the most diverse species in the North American Flora and that varieties, whose distinctions appear arbitrary, are a necessary means of communicating the diversity in morphololgy and environmental responses contained within this group.
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Brian Knaus's Website
1 - Oregon State University, Department of Botany & Plant Pathology, 2082 Cordley Hall, Corvallis, Oregon, 97331-2902, USA
2 - USDA Forest Service, Forest Genetics, Pacific Nothwest Research Station, 3200 SW Jefferson Way, Corvallis, Oregon, 97331, USA
Presentation Type: Oral Paper:Papers for Sections
Location: International Ballroom South/Hilton
Date: Wednesday, July 11th, 2007
Time: 1:15 PM