1. ¹Department of Biology, University of Oulu, Oulu, Finland
2. ²Department of Ecology and Genetics, Institute of Biology, University of Aarhus, Aarhus, Denmark

Correspondence: J Leppälä, Department of Biology, University of Oulu, PO Box 3000, FIN-90014, University of Oulu, Finland. E-mail: Johanna.Leppala@oulu.fi; Dr JS Bechsgaard, Department of Ecology and Genetics, Institute of Biology, University of Aarhus, Ny Munkegade Building 1540, 8000 Aarhus C, Denmark. E-mail: Jesper.Bechsgaard@biology.au.dk

³These authors contributed equally to this study.

Received 17 April 2007; Revised 17 August 2007; Accepted 6 September 2007; Published online 17 October 2007.

Abstract

We investigated transmission ratio distortion within an Icelandic population of Arabidopsis lyrata using 16 molecular markers unlinked to the S-locus. Transmission ratio distortion was found more often than expected by chance at the gametic level, but not at the genotypic or zygotic level. The gametic effect may be due to meiotic drive or selection acting postmeiotically. At the gametic level, 10.9% of the tests were significant, which is substantially lower than earlier observed in an interpopulation cross (allowing for differences in power)—suggesting that the high level of transmission ratio distortion in the interpopulation cross is due to population divergence. It is also substantially lower than previously observed in intrapopulation crosses at the self-incompatibility locus, suggesting inherent fitness differences of the self-incompatibility alleles. We discuss the possible role of deleterious alleles accumulating at loci under balancing selection. Zygotic effects play a larger role in the interpopulation cross than in the intrapopulation crosses suggesting that Dobzhansky–Muller incompatibilities may be accumulating between the widely diverged populations.