The Whiteman Laboratory is part of the Department of Integrative Biology at the University of California, Berkeley. We study the evolutionary, functional, genetic and molecular basis of adaptations involved in species interactions. A major focus of the lab is on the evolution of parasitism, especially parasitism of plants by insects, which is called herbivory. On the one hand, only 1/3 of the higher taxa of insects (orders) contain herbivorous species, but about 50% all all insect species are strict herbivores. Thus, there are likely barriers preventing the evolution of herbivory, such as plant toxins. But, once a lineage overcomes these barriers, it diversifies at about 2x the rate of its non-herbivorous relatives. The current assemblage of herbivorous insect species may be the most diverse guild of life ever to have evolved. Read this popular science article if you are interested.
The Diptera (true flies), in which herbivory has evolved >25 times, is our model lineage. We focus our studies on a drosophilid fly named Scaptomyza flava, a close relative of the genetic model fruit fly Drosophila melanogaster. Unlike D. melanogaster, which feeds on yeast living on rotting fruit, S. flava has shifted to parasitizing living plant leaves, including on the genetic model mustard plant Arabidopsis thaliana in the lab and nature. We use tools from model organisms and are developing new tools in vivo to study adaptations that allow S. flava to exploit the living tissues of plants as food and habitat. We are particulalry intereted in how S. flava finds the right host plants and how it uses tissue from toxic host plants. Thus, we study the behavioral, chemosensory and xenobiotic repertoire of this fly.
We also study the microevolutionary consequences of the transitions to herbivory through the lens of host plant specialization. Roughly 90% of herbivorous insect species are each specialized on a few branches of the plant tree of life, usually one plant order, family or genus (oligophagy). Why is this the case? We are conducting experimental evolutionary studies (evolve-and-resequence) coupled with population genomics surveys in the field, to determine if oligophagy is maintained by genetic tradeoffs, if alleles at loci underpinning the tradeoffs are the targets of balancing selection and if oligophagy maintains genome-wide variation. These studies highlight a renaissance in the idea that balancing selection is an important mechanism maintaining genome-wide variation within species.
A related project aims to dissect the genomic architecture and genetic basis of host plant resistance to herbivores, primarily resistance of A. thaliana to attack by adult female and larval S. flava. To identify these loci, we have taken reverse genetic approaches as well as genome wide association studies (GWAS), followed by functional genetics screens. Using A. thaliana is ecologically relevant in this case because it is a host for S. flava in nature and S. flava occurs across the range of A. thaliana.
Other projects in the lab focus on identifying the genetic basis of mustard oil detoxification in microbes living in the gut of S. flava, engineering fruit flies to dissect the genetic basis of resistance to plant toxins, the evolutionary history of the community of insects that attack the creosote plant and the co-evolutionary genomics of hummingbird bill and nectar plant floral morphology.