My work spans five major axes of research:
1) The shape of the Tree of Life, including the relationships amongst species and the factors that influence the shape of this tree.
2) Major transitions in evolution, especially the frequency of transitions, the rate at which reversals occur, and the consequences of such transitions for molecular evolutionary patterns and speciation rates.
3) Evolutionary trends, with a focus on whether there are large-scale patterns in the history of life.
4) The diversity and integrity of freshwater ecosystems, including the diversity, distributions, traits, and origins of species.
5) The diversity of polar life, which I study using DNA barcoding to discover the true extent of arctic species diversity.