McGlaughlin, Mitchell , Friar, Elizabeth .
Adaptive diversification in Dubautia laxa (Asteraceae), a widespread member of the Hawaiian silversword alliance.
Dubautia laxa Hook. & Arnott., is a widespread member of the Hawaiian silversword alliance (Asteraceae), found on five of the six major islands of the Hawaiian Archipelago. Although the distribution of D. laxa is widespread, there are four recognized subspecies that have easily identifiable morphological traits and that are sympatric on the island of Oahu. This unusual distribution raises questions about the nature of species divergence at the population level and the eventual formation of new species. For the present study 13 populations of D. laxa on five islands were sampled with nuclear microsatellites, sequence data from the floral homeotic gene ASAPETALA3/TM6, and sequence data from two chloroplast regions, the psbA-trnH intergenic spacer and the rpl16 intron. Dubautia laxa was found to contain two largely independent lineages, the hirsuta group and the laxa group. The hirsuta group is composed of all sampled populations of the widely distributed D. laxa subsp. hirsuta and a single population previously assigned to D. laxa subsp. laxa. The laxa group comprises all sampled populations of D. laxa subspp. bryanii and pseudoplantaginea, both endemic to Oahu, and all but one population of the widely distributed D. laxa subsp. laxa. The genetic data indicates that the genetically and morphologically diverse laxa group arose from the depauperate hirsuta group, which is restricted to a rare habitat type, bog margins. This finding provides insight into the processes of speciation within an adaptive radiation, where a habitat shift within a species can lead to accelerated rates of evolution and the formation of new evolutionary entities. Physical barriers among islands are also implicated in driving evolution within D. laxa, by limiting gene flow and leading to the establishment of isolated populations descended from a limited number of founders.
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1 - Rancho Santa Ana Botanical Garden, 1500 North College Avenue, Claremont, California, 91711, USA
Presentation Type: Oral Paper
Date: Monday, August 15th, 2005
Time: 1:00 PM