Josh Hough, Ph.D. student

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

Office: Earth Science Building 2044, 416-978-7177
Phone: 416-978-5603


  B. Sc. Department of Biology, Dalhousie University (2010)

 Current Position

  Ph.D. student Department of Ecology and Evolutionary Biology, University of Toronto


I have broad interests in evolutionary biology and population genetics. I am particularly interested in the evolution of sex chromosomes, sex ratios, and sexual dimorphism. For my PhD, I am using a combination of mathematical, experimental, and genomic approaches to study the evolution of these traits.

 Sex chromosome evolution

Sex chromosomes have evolved multiple times independently, and a common phenomenon associated with their evolution is the genetic deterioration of the Y chromosome. This is caused in part by suppressed X-Y recombination, which reduces the efficiency with which natural selection can eliminate deleterious mutations on the Y chromosome, or incorporate beneficial ones. Our understanding of the early stages of Y chromosome degeneration is limited, however, because sex chromosomes in many species (for example, in humans) evolved more than a hundred million years ago. The goal of this project is to study suppressed recombination and genetic deterioration in newly evolved sex chromosomes. To do this, I am analyzing the evolution of sex-linked genes in the dioecious plant Rumex hastatulus, in which sex chromosomes have evolved more recently. In particular, I am using whole genome and transcriptome sequencing to test whether this young Y chromosome has started to accumulate deleterious mutations and lose gene function as a consequence of suppressed X-Y recombination, and whether this has lead to dosage compensation of the X chromosome, as predicted by theory.

 Sex ratio evolution

Theory indicates that frequency-dependent selection will stabilize the sex ratio at 1:1 (Fisher, 1930). Biased sex ratios are common, however, and this raises questions about how and why they evolve. I am developing mathematical models to study how deviations from the 1:1 sex ratio might arise, and the conditions under which such deviations are evolutionarily stable. Recently, we have shown that, in species with sex chromosomes, selection against deleterious mutations in the haploid phase of the life cycle can counteract the effects of Fisherian sex-ratio selection and cause sex ratios to become biased at equilibrium. This work highlights the importance of gene expression and selection in the haploid phase in plants, and I am now using transcriptome sequencing to quantify this in R. hastatulus, a plant with heteromorphic sex chromosomes and female biased sex ratios.

 Evolution of sexual dimorphism

Males and females share most of their genomes, yet selection often favors traits in one sex that may be deleterious to the other. This ‘sexual conflict’ can be resolved though the evolution of sexual dimorphism, and theory predicts that the extent of sexual dimorphism that evolves will depend on the fitness costs associated with displacing either sex from their optimal trait values, which should in turn depend on condition (i.e., on the total amount of resources that an individual can allocate to trait expression). Thus, sexual dimorphism is expected to positively correlate with condition-dependence, with more strongly dimorphic traits responding more to variation in condition. Using R. hastatulus as a model system, I am conducting manipulative quantitative genetic experiments to assess the degree to which between-sex genetic correlations constrain sexual dimorphism, and whether the extent of sexual dimorphism in this species is condition-dependent.


5. Hough J, Agren Arvid, Barrett SCH, & Wright SI. (2014). Chromosomal distribution of cyto-nuclear genes in a dioecious plant with sex chromosomes. Genome Biology and Evolution (in press). doi:10.1093/gbe/evu197 (pdf)

4. Hough J, Hollister JD, Wang W, Barrett SCH, & Wright SI. (2014). Genetic degeneration of old and young Y chromosomes in the flowering plant Rumex hastatulus. Proceedings of the National Academy of Sciences 111: 7713-7718. doi:10.1073/pnas.1319227111 (pdf)

3. Hough J, Williamson R, & Wright SI. (2013). Patterns of selection in plant genomes. Annual Review of Ecology, Evolution, and Systematics 44:3.1–3.19. doi:10.1146/annurev-ecolsys-110512-135851 (pdf)

2. Hough J, Immler S, Barrett SCH, & Otto SP. (2013). Evolutionarily stable sex ratios and mutation load. Evolution 67: 1915–1925. doi:10.1111/evo.12066 (pdf)

1. Barrett SCH & Hough J. (2013). Sexual dimorphism in flowering plants. Journal of Experimental Botany 64: 67–82. doi:10.1093/jxb/ers308 (pdf)