My research focuses on how natural selection and sexual selection interact. Specifically, I am interested in how natural selection on traits that are closely related to fitness (life history traits) affects the strength of sexual selection and visa versa. For example, why is female-biased size dimorphism sometimes explained in terms of natural selection for high female fecundity (e.g., in insects, birds of prey) and other times explained in terms of sexual selection on females (e.g., in shorebirds)? Does one kind of selection predominate in some situations and not in others? I use both lab and field experiments along with theory and computer simulations to explore how natural and sexual selection interact. For example I have examined how natural selection during the postmating-prezygotic stage of the life cycle affects mating behavior and speciation. I am also currently studying how social interactions affect both insect movement and mating behavior. Brief descriptions follow, more detailed descriptions are linked on the left.
(Photograph: Mormon cricket with radio transmitter, Photo credit: Darryl Gwynne; Banner credits D. Gwynne, Gabe Miller, Greg Sword)
I am interested in the mating behavior of Mormon crickets (pictured; Anabrus simplex, Orthoptera: Tettigoniidae). These wingless katydids reach extremely high density "outbreaks" and undergo mass migrations. In some environments they experience reversals in typical sex-roles, so that females compete for mates and males are choosy. Since this reversal appears to only take place in outbreak populations, I have begun to try to understand what regulates density and migratory behavior. In collaboration with Greg Sword and Stephen Simpson at the University of Sydney, Darryl Gwynne at the University of Toronto, and Iain Couzin at Princeton University, I am testing hypotheses about the relative importance of abiotic, biotic and social factors that regulate density and migratory behavior in this katydid.
My overarching interest in the interaction between sexual selection and natural selection has led me to study speciation. In particular, some of my previous theoretical work (see below) suggested that condition dependent sexual selection can increase rates of adaptation in traits under natural selection. This work has implications for speciation. My current work on speciation takes two forms, one empirical and one theoretical. In collaboration with Maria Servedio I have recently completed a comparison of the relative strength of premating, postmating-prezygotic and postzygotic fitness costs to hybridization between two closely related species of Drosophila (D. pseudoobscura and D. persimilis). Maria and I have also constructing a model to examine how conspecific gamete preference (sperm or pollen preference) can affect the evolution of premating isolation. This model should allow us to examine how condition dependent sexual selection affects the rate of speciation.
Sex differences in autosomal recombination rates
I am also currently testing hypotheses about the role of sexual selection in the evolution of sexual differences in autosomal recombination rates. This work has both empirical and theoretical aspects. The evolution of sex differences in recombination rates is a particularly interesting example of interaction between sexual and natural selection at the molecular level. As part of this work I am beginning molecular genomic analyses comparing expression patterns for genes involved in recombination in several species of Drosophila including Drosophila ananassae, where there is recombination in both sexes.