Systematics Section / ASPT
Schenk, John J. , Liston, Aaron .
Testing the Patterns of Evolution for the Origin of Synthyris cordata (Veronicaceae).
Synthyris cordata is a serpentine endemic restricted to southwestern Oregon and northwestern California. Its range is located centrally, but not sympatrically to its sister taxon S. reniformis. Synthyris reniformis is distributed from southern Washington to northern California, and is not found on serpentine. The two taxa share many morphological characters, which has led to disagreements whether they are evolutionarily distinct.
The two objectives of our study are to test if S. cordata is evolving independently of S. reniformis, then investigate if S. cordata has evolved onto serpentine soil, or if S. reniformis has evolved off of serpentine soil. Three hypotheses are constructed to explain patterns of morphology as they relate to geography and species circumscriptions: phenotypic plasticity, species divergence, or clinal variation. The three hypotheses are translated into topologies, which are tested. Two cpDNA and one nuclear DNA marker reconstruct well-resolved clades that support the recognition of S. cordata and S. reniformis. Both phenotypic plasticity and clinal variation are rejected using bootstrap values and the Shimodaira-Hasegawa test, respectively. The maximum likelihood analysis using two best-fit models of evolution reconstruct three equally likely trees that are a subset of the fifteen trees reconstructed with parsimony. These 15 trees can be combined into three groups based on topology, which we formulate into three hypotheses of divergence: 1) S. cordata as sister to a monophyletic S. reniformis 2) a southern clade of S. reniformis as sister to northern S. reniformis and S. cordata clades 3) or the most recent common ancestor gave rise to three lineages as seen by a trifurcation. The paraphyly of S. reniformis in Hypothesis two is consistent with a derivation of the serpentine endemic S. cordata from a non-serpentine ancestor, while Hypotheses one and three are equivocal and dependent on the condition of serpentine tolerance of their common ancestor.
1 - Oregon State University, Department of Botany and Plant Pathology, 2082 Cordley Hall, Corvallis, Oregon, 97331-2902, USA
Presentation Type: Paper
Location: Cottonwood A (Snowbird Center)
Date: Tuesday, August 3rd, 2004
Time: 8:00 AM