Systematics/Phytogeography / Taxonomie/ Section
Knaus, Brian , Cronn, RC , Liston, Aaron .
A fistful of Astragalus: incipient speciation in the American West?
The infra-specific ranks (subspecies and variety) have traditionally been considered taxa which may be differentiating into new species. The most taxon rich species in the United States flora is Astragalus lentiginosus, containing 35 taxonomic varieties.
We implement morphological and molecular (five chloroplast microsatellites) methodologies to test these taxonomic hypotheses and to characterize levels of divergence within the group. Morphological analyses indicated strong correlations with climatic parameters yet fail to identify regions of discontinuity among the varieties. Chloroplast microsatellite analysis revealed 57 haplotypes, however this diversity is shared among varieties and does not appear to follow an isolation by distance pattern. These data are interpreted as an instance of incomplete lineage sorting: clinal morphologies indicate a level of cohesiveness to the group while molecular diversity does not appear to support taxonomic or geographical hypotheses. In order to explore this hypothesis, coalescent simulations were performed to determine which parameters may have led to the pattern observed in the empirical dataset. Simulations suggest that sorting of currently observed genetic diversity may take on the order of hundreds of thousands of years. Astragalus lentiginosus displays a continuum of diversity which is so profound that it has been recognized at the taxonomic level. Molecular data appear to reflect this diversity in that there are numerous haplotypes yet no clear distinctions can be made. While this diversity appears relatively continuous it is important to recognize existing taxonomy in order to preserve (potential) incipient lineages.
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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
incomplete lineage sorting
Presentation Type: Oral Paper:Papers for Sections
Date: Tuesday, July 29th, 2008
Time: 10:30 AM