We study adaptations that arise from species interactions. We primarily use plants as model hosts and herbivorous insects as model parasites. A major focus of the lab is in identifying the genomic basis of adaptations that are linked to the evolution of parasitism, especially parasitism of plants by insects. On the one hand, only 1/3 of insect 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 this barrier, they diversify about 2x the rate of non-herbivorous relatives. It is likely that the current assemblage of herbivorous insect species are the most diverse guild of life ever to have evolved.
The Diptera (true flies), in which herbivory has evolved >25 times, is our model lineage and we focus our studies on a drosophilid fly named Scaptomyza flava, which is 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 feeding on living plant leaves, including on the genetic model mustard plant Arabidopsis thaliana in the lab and in nature. We use the tools of both Drosophila and Arabidopsis genetic and genomics to study the adaptations that allow S. flava to exploit the living tissues of plants as food and habitat.
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, the genomics of host specialization and reproductive isolation in parasitic mistletoes, and the co-evolutionary genomics of hummingbird bill and nectar plant floral morphology. The Whiteman Laboratory is part of the Department of Integrative Biology at the University of California, Berkeley.