MBE Advance Access published online on January 21, 2008
Molecular Biology and Evolution, doi:10.1093/molbev/msn016
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Research Article |
A 15-Million-Year-Old Genetic Bottleneck
1 Section of Ecology, Behavior and Evolution, Department of Biological Sciences, University of California San Diego, 9500 Gilman Drive, La Jolla CA 92093-0116, USA
2 Department of Biological Sciences, M/C 067, University of Illinois at Chicago, 840 West, Taylor St., Chicago, IL 60607, USA
3 Department of Biology, Box 90338, Duke University, Durham, NC 27708, USA
4 Department of Biology and Burke Museum, University of Washington, Seattle, WA 98195, USA
5 Department of Biology, University of Utah, 257 South 1400 East, Salt Lake City, UT 84112, USA
6 Author for correspondence: email jkohn{at}ucsd.edu; phone 858-534-8233; fax 858-534-7108
Received for publication August 2, 2007. Revision received December 17, 2007. Accepted for publication December 28, 2007.
Balancing selection preserves variation at the self-incompatibility locus (S-locus) of flowering plants for tens of millions of years, making it possible to detect demographic events that occurred prior to the origin of extant species. In contrast to other Solanaceae examined, self-incompatible species in the sister genera Physalis and Witheringia share restricted variation at the S-locus indicative of an ancient bottleneck that occurred in a common ancestor. We sequenced 14 S-alleles from the subtribe Iochrominae, a group that is sister to the clade containing Physalis and Witheringia. At least six ancient S-allele lineages are represented among these alleles demonstrating that the Iochrominae taxa do not share the restriction in S-locus diversity. Therefore the bottleneck occurred after the divergence of the Iochrominae from the lineage leading to the most recent common ancestor of Physalis and Witheringia. Using cpDNA sequences, three fossil dates, and a Bayesian relaxed molecular clock approach, the crown group of Solanaceae was estimated to be 51 MY old and the restriction of variation at the S-locus occurred 14.0 - 18.4 MY before present. These results confirm the great age of polymorphism at the S-locus and the utility of loci under balancing selection for deep historical inference.
Key Words: Balancing selection • genetic bottleneck • S-locus • self-incompatibility • shared ancestral polymorphism • Solanaceae
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