RECONCILING EXTREMELY STRONG BARRIERS WITH HIGH LEVELS OF GENE EXCHANGE IN ANNUAL SUNFLOWERS
Article first published online: 3 JAN 2012
© 2011 The Author(s). Evolution© 2011 The Society for the Study of Evolution.
Volume 66, Issue 5, pages 1459–1473, May 2012
How to Cite
Sambatti, J. B.M., Strasburg, J. L., Ortiz-Barrientos, D., Baack, E. J. and Rieseberg, L. H. (2012), RECONCILING EXTREMELY STRONG BARRIERS WITH HIGH LEVELS OF GENE EXCHANGE IN ANNUAL SUNFLOWERS. Evolution, 66: 1459–1473. doi: 10.1111/j.1558-5646.2011.01537.x
- Issue published online: 20 APR 2012
- Article first published online: 3 JAN 2012
- Accepted manuscript online: 12 DEC 2011 04:58PM EST
- Received March 24, 2011, Accepted October 25, 2011, Data Archived: Dryad doi:10.5061/dryad.r4j63pg0
- Effective population size;
- reproductive isolation;
- species divergence
In several cases, estimates of gene flow between species appear to be higher than we might predict given the strength of interspecific barriers separating these species pairs. However, as far as we are aware, detailed measurements of reproductive isolation have not previously been compared with a coalescent-based assessment of gene flow. Here, we contrast these two measures in two species of sunflower, Helianthus annuus and H. petiolaris. We quantified the total reproductive barrier strength between these species by compounding the contributions of the following prezygotic and postzygotic barriers: ecogeographic isolation, reproductive asynchrony, niche differentiation, pollen competition, hybrid seed formation, hybrid seed germination, hybrid fertility, and extrinsic postzygotic isolation. From this estimate, we calculated the probability that a reproductively successful hybrid is produced: estimates of Phyb range from 10−4 to 10−6 depending on the direction of the cross and the degree of independence among reproductive barriers. We then compared this probability with population genetic estimates of the per generation migration rate (m). We showed that the relatively high levels of gene flow estimated between these sunflower species (Nem= 0.34–0.76) are mainly due to their large effective population sizes (Ne > 106). The interspecific migration rate (m) is very small (<10−7) and an order of magnitude lower than that expected based on our reproductive barrier strength estimates. Thus, even high levels of reproductive isolation (>0.999) may produce genomic mosaics.