We study adaptations that arise from species interactions. We aim to identify the evolutionary processes shaping these adaptive phenotypes and genotypes and their functional genetic basis.
Lately, we have been studying host-parasite co-evolutionary genetics. We primarily use plants as model hosts and herbivorous insects as model parasites. Our current focus is on the transition from free-living to herbivorous (parasitic) life histories in insects and the evolutionary consequences of these transitions. A main goal is to understand the mechanisms underpinning these life history transitions by dissecting the behavioral, morphological, neurological and physiological traits, and the genes that underpin them, that are linked to herbivory.
The Diptera (true flies), in which herbivory has evolved >25 times, is our model lineage. To study these phenomena in great detail, we have developed a genomically tractable plant-herbivore system. The herbivore is 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, incuding on the genetic model mustard plant Arabidopsis thaliana in the lab and in nature.
We also study the microevolutionary consequences of the transitions to herbivory through the lens of host plant specialization. Roughly 90% of herbivorous 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.