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Patterns and Mechanisms of Evolution of Island Plants

Remington, David L. [1], Robichaux, Robert H. [2].

Genome-level analysis of speciation mechanisms in the Dubautia arborea- D. ciliolata complex.

Plant taxa in lineages undergoing adaptive radiation are often highly interfertile, and the mechanisms that maintain species integrity in these lineages are unclear. Dubautia arborea and D. ciliolata are closely-related species in the Hawaiian silversword alliance (Asteraceae- Madiinae) that exhibit strong morphological divergence, yet are completely interfertile and occur in parapatry with occasional hybridization. To examine the roles of selection, genetic drift, and gene flow in speciation, we scored individuals from two populations each of D. arborea and D. ciliolata and from phenotypically parental individuals in a hybrid zone for 166 AFLP markers. Interspecific molecular differentiation was low (FST = 0.09), in contrast with nearly complete morphological differentiation for six quantitative characters. The contrasting parental phenotypes in the hybrid zone showed similar levels of molecular differentiation, suggesting that these individuals are not of recent hybrid origin. A Bayesian analysis of population ancestry, however, failed to distinguish D. arborea and D. ciliolata phenotypes as two distinct populations. The ancestry analysis identified a minimum of five source populations for the sampled individuals, three consisting of D. ciliolata phenotypes and two of D. arborea phenotypes. These results indicate that both species may consist of mosaics of hybrid-origin populations, which were subsequently selected independently for the contrasting parental phenotypes that confer adaptation to the respective environments in which the species occur. These results will be discussed in the context of recently-proposed genic models of speciation and species cohesiveness. Implications for the genetic mechanisms and ecological processes involved in speciation will also be discussed.

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1 - University of North Carolina Greensboro, Department of Biology, Po Box 26170, Greensboro, North Carolina, 27402-6170, USA
2 - University of Arizona, Department of Ecology and Evolutionary Biology, P.O. Box 210088, Tucson, Arizona, 85721, USA

Hawaiian silversword alliance
gene flow

Presentation Type: Symposium or Colloquium Presentation
Session: 50-4
Location: Salon J - Austin Grand Ballroom/Hilton
Date: Wednesday, August 17th, 2005
Time: 3:30 PM
Abstract ID:429

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