Year of Award


Document Type


Degree Type

Master of Science (MS)

Degree Name

Organismal Biology and Ecology

Department or School/College

Division of Biological Sciences

Committee Chair

Lila Fishman

Commitee Members

Douglas Emlen, Jeffrey Good, John McCutcheon


hybrid sterility, chromosomal rearrangements, inversion, translocation, speciation


University of Montana

Subject Categories

Evolution | Genetics


Chromosomal rearrangements can contribute to the evolution of postzygotic reproductive isolation directly, by disrupting meiosis in F1 hybrids, or indirectly, by suppressing recombination among genic incompatibilities. Because direct effects of rearrangements on fertility imply fitness costs during their spread, understanding the mechanism of F1 hybrid sterility is integral to reconstructing the role(s) of rearrangements in speciation. In hybrids between monkeyflowers Mimulus cardinalis and M. lewisii, rearrangements contain all quantitative trait loci (QTLs) for both premating barriers and pollen sterility, suggesting that they may have facilitated speciation in this model system. I used artificial chromosome doubling and comparative mapping to test whether heterozygous rearrangements directly cause underdominant male sterility in M. lewisii-M. cardinalis hybrids. Consistent with a direct chromosomal basis for hybrid sterility, synthetic tetraploid F1s showed highly restored fertility (83.4% pollen fertility) relative to diploids F1s (36.0%). Additional mapping with M. parishii-M. cardinalis and M. parishii-M. lewisii hybrids demonstrated that underdominant male sterility is caused by one M. lewisii-specific and one M. cardinalis-specific reciprocal translocation, but that inversions had no direct effects on fertility. I discuss the importance of translocations as causes of reproductive isolation, and consider models for how underdominant rearrangements spread and fix despite intrinsic fitness costs.



© Copyright 2015 Angela M. Stathos