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Genetics. Published Articles Ahead of Print: February 4, 2007, Copyright © 2007
doi:10.1534/genetics.106.064469

A more recent version of this article appeared on April 1, 2007.
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REGULAR RESEARCH PAPERS

Rampant gene exchange across a strong reproductive barrier between the annual sunflowers, Helianthus annuus and H. petiolaris

Yoko Yatabe 1, Nolan C. Kane 2, Caroline Scotti-Saintagne 1 and Loren H. Rieseberg 2*

1 Indiana University
2 University of British Columbia

* To whom correspondence should be addressed. E-mail: lriesebe{at}indiana.edu.

Submitted on August 6, 2006
Revised on January 11, 2007
Accepted on 20 January 2007


  Abstract
Plant species may remain morphologically distinct despite gene exchange with congeners, yet little is known about the genome-wide pattern of introgression between species. Here we analyze the effects of persistent gene flow on genomic differentiation between the sympatric sunflower species, Helianthus annuus and H. petiolaris. While the species are strongly isolated in testcrosses, genetic distances at 108 microsatellite loci and 14 sequenced genes are highly variable and much lower (on average) than for more closely related but historically allopatric congeners. Our analyses failed to detect a positive association between levels of genetic differentiation and chromosomal rearrangements (as reported in a prior publication) or proximity to QTLs for morphological differences or hybrid sterility. However, a significant increase in differentiation was observed for markers within five cM of chromosomal breakpoints. Together, these results suggest that islands of differentiation between these two species are small, except in areas of low recombination. Furthermore, only microsatellites associated with ESTs were identified as outlier loci in tests for selection, which might indicate that the ESTs themselves are the targets of selection rather than linked genes (or that coding regions are not randomly distributed). In general, these results indicate that even strong and genetically complex reproductive barriers cannot prevent widespread introgression.

Key Words: EST, adaptive differentiation, introgression, microsatellites, sunflower




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