Culley, Theresa M. , Wallace, Lisa Ellen , Weller, Stephen G. , Nepokroeff, Molly , Kuenzi, Ashley , Sakai, Ann K. , Roy, Tilottama , Wagner, Warren L. .
The evolution of sexual dimorphism in a hybrid zone in Hawaiian Schiedea .
Analysis of hybrid zones of flowering plants have provided a wealth of information regarding factors affecting interspecific gene flow, speciation and the nature of pre- and post-zygotic barriers, but their role in the evolution of sexual dimorphism has remained relatively unexplored. In the endemic Hawaiian genus Schiedea, hybridization between gynodioecious, wind-pollinated S. salicaria and hermaphroditic, largely selfing S. menziesii has been hypothesized to be the mechanism through which a male sterility allele has been introduced into S. menziesii. In this species, females are virtually undetectable in the field but they appear in plants grown in the greenhouse from field-collected seed. To test the prediction that gene flow in a hybrid zone should occur largely from the outcrossing to the selfing species, and that selection should favor morphological traits associated with outcrossing, molecular traits (nuclear and chloroplast microsatellites, chloroplast DNA sequences) and morphological traits (e.g. inflorescence length and number of flowers, leaf length and width) were analyzed for a hybrid zone on the island of Maui. Nuclear microsatellite data supported the hybrid status of putative hybrid individuals, which shared alleles with both species but clustered with S. menziesii in ordination space. An analysis of five non-coding chloroplast regions, including four intergenic spacers (petL-psbE, ndhJ-trnF , petN-psbM, psbM-trnD) and the intron of rpS16, revealed many unique multilocus chloroplast haplotypes with no hybrid individual containing a haplotype identical to either species. This was also the case for five chloroplast microsatellites containing single base repeats. In terms of morphology, S. menziesii differed from S. salicaria primarily in having fewer-flowered, more laterally condensed inflorescences, and longer, narrow, three-nerved leaves. Most hybrids were more similar morphologically to the outcrossing S. salicaria than to S. menziesii and females were detected in the hybrid population. Taken together, these data are largely consistent with our hypothesis that sexual dimorphism is evolving in S. menziesii following transmission of a male sterility allele from S. salicaria through a hybrid zone.
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1 - University of Cincinnati, Department of Biological Sciences, 614 Rieveschl Hall, Cincinnati, Ohio, 45221, USA
2 - Mississippi State University, Department of Biological Sciences, 208 Harned Hall Lee Blvd., Starkville, MS, 39762, USA
3 - University of California Irvine, Department of Ecology & Evolutionary Biology, 321 Steinhaus Hall, Irvine, California, 92697-2525, USA
4 - University of South Dakota, Department of Biology, 414 East Clark Street, Vermillion, South Dakota, 57069, USA
5 - University of Cincinnati, Biological Sciences, 614 Rieveschl Hall, Cincinnati, OH, 45221-0006, USA
6 - National Museum of Natural History, Smithsonian Institution, Botany, P.O. Box 37012, MRC 166, Washington, DC, 20013-7012, USA
Presentation Type: Oral Paper:Papers for Topics
Location: 556A/Convention Center
Date: Tuesday, August 3rd, 2010
Time: 10:15 AM