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MBE Advance Access originally published online on January 21, 2008
Molecular Biology and Evolution 2008 25(4):655-663; doi:10.1093/molbev/msn016
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© The Author 2008. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

Research Articles

A 15-Myr-Old Genetic Bottleneck

Timothy Paape*, Boris Igic{dagger}, Stacey D. Smith{ddagger}, Richard Olmstead§, Lynn Bohs|| and Joshua R. Kohn*

* Section of Ecology, Behavior and Evolution, Department of Biological Sciences, University of California, San Diego
{dagger} Department of Biological Sciences, University of Illinois at Chicago
{ddagger} Department of Biology, Duke University
§ Department of Biology and Burke Museum, University of Washington
|| Department of Biology, University of Utah

E-mail: jkohn{at}ucsd.edu.

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, SI species in the sister genera Physalis and Witheringia share restricted variation at the S-locus. This restriction is 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 6 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, 3 fossil dates, and a Bayesian-relaxed molecular clock approach, the crown group of Solanaceae was estimated to be 51 Myr old and the restriction of variation at the S-locus occurred 14.0–18.4 Myr 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

Scott Edwards, Associate Editor


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