Genetics. Published Articles Ahead of Print: January 16, 2006, Copyright © 2006
doi:10.1534/genetics.105.053686


A more recent version of this article appeared on April 1, 2006.

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A simple genetic incompatibility causes hybrid male sterility in Mimulus

Andrea Sweigart 1*, Lila Fishman 2 and John Willis 1

1 Duke University
2 University of Montana

* To whom correspondence should be addressed. E-mail: als21{at}duke.edu.

Submitted on November 17, 2005
Revised on January 1, 2006
Accepted on 10 January 2006


Abstract

Much evidence has shown that postzygotic reproductive isolation (hybrid inviability or sterility) evolves by the accumulation of interlocus incompatibilities between diverging populations. Although in theory only a single pair of incompatible loci is needed to isolate species, empirical work in Drosophila has revealed that hybrid fertility problems are often highly polygenic and complex. In this report, we investigate the genetic basis of hybrid sterility between two closely related species of monkeyflower, Mimulus guttatus and M. nasutus. In striking contrast to Drosophila systems, we demonstrate that nearly complete hybrid male sterility in Mimulus results from a simple genetic incompatibility between a single pair of heterospecific loci. We have genetically mapped this sterility effect: the M. guttatus allele at the hybrid male sterility 1 (hms1) locus acts dominantly in combination with recessive M. nasutus alleles at the hybrid male sterility 2 (hms2) locus to cause nearly complete hybrid male sterility. In a preliminary screen to find additional small-effect male sterility factors, we identified one additional locus that also contributes to some of the variation in hybrid male fertility. Interestingly, hms1 and hms2 also cause a significant reduction in hybrid female fertility, suggesting that sex-specific hybrid defects might share a common genetic basis. This possibility is supported by our discovery that recombination is dramatically reduced in a cross involving a parent with the hms1-hms2 incompatibility.

Key Words: Mimulus, hybrid incompatibility, male sterility, postzygotic reproductive isolation, speciation




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