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Redpath Museum & Dept. of Biology

McGill University

859 Sherbrooke St. W.

Montréal, QC H3A 0C4

email: dieta.hanson(at)mail.mcgill.ca

Stickleback Evolution

For my PhD thesis, I am interested in exploring the process of ecological speciation, and resolving to what extent natural selection plays a deterministic role in this phenomenon.  A particular kind of evolution, where populations evolve similar traits in response to similar environments (called parallel evolution because the trait trajectories of both populations are parallel to one another), can be a powerful way to demonstrate that selection is, indeed, deterministic.  Luckily for me, the Threespine Stickleback (Gasterosteus aculeatus), a small fish that has invaded freshwater environments from an ocean source repeatedly since the last ice age, demonstrates parallel evolution in several traits that allowed it to adapt to life in lakes vs. streams.  I am particularly interested in quantifying parallelism in the genetic response to selection, measured through gene expression analysis.  This will help clarify whether phenotypic parallelism (which is already well-documented) is reflected in genetic parallelism.  Looking at a later stage in ecological speciation, reproductive isolation, is another crucial part of the story.  I want to determine if the timing of reproduction is different in lakes and streams (maybe as a response to different temperatures or flow rates), and whether this difference is parallel across many lake-stream systems. 

Opisthobranch Phylogenetics

The focus of my MSc was Haminoea japonica, a species of opisthobranch mollusc (sea slug) that was originally described from Japan.  Starting in the 1980s, the species was reported from the west coast of North America (from British Columbia to Northern California), France, Italy, Spain, and South Korea.  I used mitochondrial DNA sequences to determine that these new populations were invasive and had come from the north-eastern coast of Japan, likely hitchhikers on exports of oyster seed.  In addition to possible negative effects on native Haminoea species, at least one invasive population of Haminoea japonica carries a schistosome parasite that has caused swimmer’s itch outbreaks in public swimming areas.  These results are important to inform efforts to prevent further spread of this species, especially to areas that have economic dependence on public swimming beaches.  I am also still involved in the similar case of Melanochlamys diomedea, another slug that has a range spanning most of the North Pacific, from South Korea to Southern California.  Genetic analysis has revealed a highly divergent clade in San Francisco Bay, a place infamous for its high rate of species invasions.  We are currently collecting specimens from Australia and South Africa to determine whether either of these locations are the source of the non-native group in California.