My research investigates the ecological forces responsible for the origin and persistence of species and the evolution of differences between them in resource use, body form, and mating preferences. I am especially interested in experimental studies of natural selection in wild populations, the role of natural and sexual selection on the evolution of reproductive isolation, the effect of interactions between species on the evolution of species differences, and the genetic factors underlying divergence.
Principally, I study the ecology of recent adaptive radiations. My earliest work was carried out on Darwin's famous finches in the Galápagos Islands. More recently I have been working on a mini-explosion of new species of threespine sticklebacks in lakes of coastal British Columbia, Canada. The species are among the youngest on earth and occur in lakes that are less than 12,000 years old. No more than two species occur in any one lake, but pairs of species in different lakes seem to have evolved completely independently of other pairs. They have all kinds of great properties that allow us to address very basic questions concerning the roles of resources, species interactions, phenotypic plasticity, sexual selection and other factors in the evolution of diversity. They produce viable and fertile hybrids, making it possible to investigate the genetic basis of species differences using hybrids.
Our research on sticklebacks presently has three main directions. The first concerns the role of interactions (competition and predation) in the evolution of differences between species. Our work in this area includes experiments in ponds in which we measure how natural selection on a species is changed when another species (e.g., a competitor) is added to its environment. The second area concerns the origin and persistence of species themselves, especially the role of ecological selection and reinforcement in the buildup of mating incompatibilities between populations exploiting different environments, and their persistence in the face of gene flow. The third area, in collaboration with David Kingsley at Stanford University and Katie Peichel at the Fred Hutchinson Cancer Research Center, investigates the genetic basis of species differences.
The question of species persistence has lately taken on a new urgency, with the rapid rate at which the stickleback species pairs are becoming extinct. Part of our work is dedicated to understanding why this is occurring, why now, and what can be done to forestall the doom of the species pairs that remain.