Andrew Simpson, M.Sc. student

Department of Ecology and Evolutionary Biology
University of Toronto
25 Willcocks Street
Toronto, Ontario, Canada
M5S 3B2

Office: Earth Science Building 2043
Phone: 416-978-5603


  B. Sc.   (2011) Department of Biology, Queen’s University, Canada

 Current Position

 M.Sc. student

I am currently a member of Professor Barrett’s lab in the Department of Ecology and Evolutionary Biology, University of Toronto, Canada.



I am interested in the fields of plant evolutionary genetics, population genetics, and phylogeography. My research focuses on issues related to incipient speciation, the role of hybridization in contributing to genetic structure within and between populations, and sex-specific differences in hybrid fitness.

Speciation in sexually reproducing organisms is driven by reproductive isolation, whereby individuals from divergent lineages accumulate barriers to reproducing with one another. One way by which postzygotic reproductive isolation arises is that chromosomal rearrangements inhibit gene flow between diverging lineages1. Another postzygotic barrier to hybridization between divergent lineages is the accumulation of Dobzhansky-Muller Incompatibilities (DMIs): deleterious epistatic interactions among loci that occur because of incompatibilities between the parental genetic backgrounds2. Accumulation of DMIs on sex chromosomes is one of the most widely accepted explanations for the phenomenon of Haldane’s rule, which states that hybrid sterility and inviability is more likely to occur in the heterogametic sex in F1 hybrid crosses3,4. DMIs contribute disproportionately to sterility and inviability in the heterogametic sex because only dominant x-linked incompatibility genes will affect homogametic hybrids, whereas dominant and recessive x-linked incompatibility genes will affect heterogametic hybrids5. It is likely that multiple processes contribute to Haldane’s rule, and a second cause is explained by incompatibilities of X and Y (or Z and W) chromosomes from divergent lineages6. When brought together in hybrids, these incompatibilities become manifest, but only for heterogametic individuals; thus any deleterious effects are restricted to that sex.

Rumex Fem & Male

Rumex hastatulus

I am using the dioecious, annual, plant Rumex hastatulus to investigate the role of chromosomal rearrangements in shaping population structure, affecting hybridization rates and patterns of introgression, and contributing to Haldane’s rule. Rumex hastatulus is a good candidate for such investigations because it has a short generation time, an historically delimited hybrid zone, and both XX/XY and XX/XY1Y2 sex chromosome systems. I will address these topics using a combination of controlled crosses in the glasshouse, sampling of the hybrid zone, and next-generation sequencing.


 Literature Cited

    1. Rieseberg LH. 2001. Chromosomal rearrangements and speciation. Trends in Ecology & Evolution 16: 351-358.
    2. Orr HA. 1995. The population genetics of speciation: the evolution of hybrid incompatibilities. Genetics 139: 1805-1813.
    3. Haldane JBS. 1922. Sex ratio and unisexual sterility in hybrid animals. Journal of Genetics 12: 101-109.
    4. Orr HA. 1997. Haldane’s rule. Ecology 28:195-218.
    5. Turelli M, Orr HA. 1995. The dominance theory of Haldane’s rule. Genetics 140: 389-402.
    6. Coyne JA. The genetic basis of Haldane’s rule. Nature 314: 736-738.