The genomic basis of speciation: mitonuclear conflict and speciation in stickleback.

The successful applicant for this multidisciplinary, international project will combine cutting-edge bioinformatics and physiological assays of mitochondrial function with traditional genetic analysis, behavioural experiments and fieldwork to assess the contribution of mitochondrial dysfunction to speciation in an evolutionary model species, the three-spined stickleback. Ecological fieldwork will take place in the Scottish Outer Hebrides, and there will be opportunities for visits to collaborating labs in Germany and Canada.

Mitochondria, the powerhouse of all eukaryotic cells, are intimately involved in many cellular processes. “Co-adapted gene complexes” comprised of both nuclear and mitochondrial genes must work closely together in the production of energy by oxidative phosphorylation (oxphos) and other processes. The breakdown of this essential biochemical cooperation results in organismal dysfunction including many human diseases. Dysfunction may arise when populations come into secondary contact following divergence, and untested combinations of mitochondrial and nuclear genes must work together. This has stimulated a novel hypothesis for the process of speciation, Darwin’s “mystery of mysteries”. Any breakdown of nuclear-mitochondrial coadaptation following hybridisation between divergent taxa may be a common cause of reproductive isolation (the inability of individuals from different populations to successfully mate with each other). Thus far, this idea has been examined in only a handful of organisms, and only once in vertebrates. This studentship will investigate the contribution of mitonuclear conflict to speciation in stickleback, a small fish with excellent genomic resources.

Three-spined stickleback have repeatedly colonised freshwater from the sea. The contrasting energetic and osmotic demands of marine and freshwater environments exert strong selection on genes involved in oxphos pathways, potentially favouring strong selection on nuclear-mitochondrial coadaptation. On the Scottish island of North Uist there are hybrid zones between marine and freshwater stickleback populations that originate from distinct mitochondrial clades that are ~120,000 years diverged. Hybridisation in these contact zones is strongly asymmetric, with freshwater mtDNA introgressing into marine fish, but not vice versa. This is strongly suggestive of mitonuclear conflict contributing to speciation in these fish.

Training rotations for this project will allow students to learn skills directly relevant to the project, with substantial components of wet lab molecular genetics, physiology and bioinformatics.

The project will be based in the MacColl lab, http://ecology.nottingham.ac.uk/AndrewMacColl/index.php, a friendly, dynamic and well-funded group, embedded in a wider cohesive group of ecologists and evolutionary biologists http://ecology.nottingham.ac.uk/index.html.