Evolutionary and ecological genetics of Wolbachia and their Drosophila hosts
We are a collaborative team of researchers studying Drosophila-Wolbachia interactions, physiological adaptation, and speciation. Many of our current projects combine approaches from genomics, genetics, cell biology, and population biology to better understand Wolbachia spread within and between host species. This knowledge is crucial to improve the efficacy of Wolbachia from Drosophila as a biocontrol of vector-borne disease (particularly dengue and now Zika). Our field work takes us from local orchards to sites overseas where we sample Wolbachia-infected flies from Africa, Asia, Australia and South America. We are fortunate to conduct our lab research at the University of Montana in beautiful Missoula, Montana.
Local adaptation and reproductive isolation
Our projects also evaluate local adaptation within host species, and the evolution of reproductive isolation between species. Much of our focus is currently on the D. yakuba clade of host flies. Drosophila santomea is endemic to the island of São Tomé in west Africa. At intermediate altitudes on Pico de São Tomé, D. santomea hybridizes with its sister species D. yakuba. Drosophila yakuba also occurs on the nearby island Bioko. In collaboration with Daniel Matute's group, we recently identified a hybrid zone on Bioko between D. yakuba and the third species in the clade, D. teissieri. We estimate that these species diverged about 3 million years ago making this the most divergent hybrid zone in the genus. Interestingly, our genomic analyses indicate that only F1 progeny of D. yakuba females and D. teissieri males occur on Bioko. Field and laboratory analyses suggest that a maladaptive combination of D. yakuba behavior and D. teissieri physiology makes these hybrids particularly unfit. Current analyses are evaluating cytoplasmic effects that might explain the lack of hybrids produced by D. teissieri mothers.
Mitochondria reside within the cytoplasm and are co-transmitted with Wolbachia. Mitochondria are haploid, have high mutation rates, and lack recombination—this contributes to a lower effective population size (Ne) of mitochondria relative to the nuclear genome. Our work has shown that despite this reduction in Ne, genes in the mitochondria experience a similar efficacy of purifying selection as those in the nuclear genome, in at least flies and humans. Because mitochondria interact with genes in the nucleus we are exploring the consequences of Wolbachia sweeps on mt x nuclear interactions; and more generally, we are evaluating the influence of mt-Wolbachia interactions on host fitness.
We are currently funded by the National Institutes of Health (NIH) to determine the effects of Wolbachia on host physiology and fitness that enable Wolbachia spread. We are grateful for this funding and for past funding from the NIH, the National Science Foundation, and several other agencies.