Intraspecific biodiversity and speciation in Atlantic Canadian fishes

How species form is a key question in biology. One theory proposes that speciation is driven by ecology - differences in food or habitat use lead parts of a population to become reproductively isolated, forming new species. Ecological speciation may be important for fishes, because their environments may lack physical barriers invoked in other theories of how speciation occurs. My research examines two fishes that are undergoing ecological speciation, yet challenge notions of how it can occur. Rainbow Smelt in lakes have small bodies specialized for eating plankton, but in a few lakes, a Large' form, specialized for eating fish, also occurs. Small and Large smelt are reproductively isolated, but how this has developed is a mystery, given that they breed by spreading eggs and sperm at night in places and times that overlap. Two forms of Threespine Stickleback, White' and Common', co-occur in Nova Scotia. Male White and Common sticklebacks differ in colour and breeding behaviour, and are reproductively isolated, but lab studies show they can interbreed. They may be different species, but they have no known ecological differences.*I will investigate how speciation is occurring in these fishes by examining how their genomes have diverged, and linking that information to ecological traits. I will sequence entire genomes of White and Common sticklebacks, and scan the genomes of smelt using a related method. I will examine the parasites the fish carry, because parasites reflect prey choice, habitat, and predator exposure, and so offer clues about ecology. I will examine genes involved in fighting off parasites, because these too reflect ecological adaptations, and because they also influence mate choice, and so may be involved in species formation. In smelt, I will use chemical traces (stable isotopes) to investigate feeding behaviour. In both species, I will examine details of body form as further clues about ecological divergence.*The genome data will reveal whether genes involved in divergence are organized in ways that might enable divergence to develop despite some interbreeding. We may learn, particularly in stickleback, exactly which genes are most important for speciation. In both smelt and stickleback, the genomic data will also tell us whether parallel divergence in phenotype (Small vs. Large and White vs. Common) in different locations has occurred involving the same changes in the genome. The other data will provide many clues about the ecological basis of divergence in stickleback and smelt. *This research will advance knowledge of how ecological speciation can occur, particularly in fishes. It will contribute to knowledge of Canadian biodiversity, and for smelt, will provide information that may inform management and conservation measures. Two PhD students, one MSc student, and five undergraduate students will be trained in advanced methods of genomic and ecological analyses.*