Journal Article

A 15-Myr-Old Genetic Bottleneck

Timothy Paape, Boris Igic, Stacey D. Smith, Richard Olmstead, Lynn Bohs and Joshua R. Kohn

in Molecular Biology and Evolution

Published on behalf of Society for Molecular Biology and Evolution

Volume 25, issue 4, pages 655-663
Published in print April 2008 | ISSN: 0737-4038
Published online January 2008 | e-ISSN: 1537-1719 | DOI:
A 15-Myr-Old Genetic Bottleneck

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  • Evolutionary Biology
  • Molecular and Cell Biology


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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.

Keywords: balancing selection; genetic bottleneck; S-locus; self-incompatibility; shared ancestral polymorphism; Solanaceae

Journal Article.  6276 words.  Illustrated.

Subjects: Evolutionary Biology ; Molecular and Cell Biology

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