Evolution of herbivory
The phenotypes of parasites are a case-study in convergent evolution. A major, unsolved problem is whether molecular convergence underpins phenotypic convergence in parasites. Independent transitions to plant parasitism within the family Drosophilidae provide an excellent opportunity in which to test the hypothesis that convergent phenotypic evolution is underpinned by convergent molecular genetic patterns.
We are leading an effort to develop genomically and genetically tractable model herbivores of the model plant Arabidopsis thaliana and relatives: Leafmining flies nested in the paraphyletic Drosophila lineage (called Scaptomyza). Because some members of the lineage can be reared on media or on Arabidopsis plants, the genetic tools for Drosophila and Arabidopsis can be leveraged to study both sides of the plant-herbivore equation. Our recent paper describes the system (Whiteman et al., Mol. Ecol. 2011). PERT Postdoctoral fellow Rick Lapoint is leading our effort to inbreed, sequence and assemble the genome of S. flava and Rick is also reconstructing a comprehensive phylogeny of the Scaptomyza lineage in collaboration with Professor Patrick O'Grady at UC-Berkeley.
We are leading an effort to develop genomically and genetically tractable model herbivores of the model plant Arabidopsis thaliana and relatives: Leafmining flies nested in the paraphyletic Drosophila lineage (called Scaptomyza). Because some members of the lineage can be reared on media or on Arabidopsis plants, the genetic tools for Drosophila and Arabidopsis can be leveraged to study both sides of the plant-herbivore equation. Our recent paper describes the system (Whiteman et al., Mol. Ecol. 2011). PERT Postdoctoral fellow Rick Lapoint is leading our effort to inbreed, sequence and assemble the genome of S. flava and Rick is also reconstructing a comprehensive phylogeny of the Scaptomyza lineage in collaboration with Professor Patrick O'Grady at UC-Berkeley.
Evolution of host specificity--I. Comparative and functional genetics of detoxification repertoires
We use comparative genomics and functional genetics approaches to understand adaptation to extreme environments in Drosophila and relatives. We are focusing on mustard oil detoxification in Scaptomyza. Metabolomics studies of mustard oil breakdown products are currently underway with Professor Jonathan Gershenzon, which aim to identify the major pathways involved in detoxification. This allows for candidate gene approaches and systems biology approaches to study the genetic bases of detoxification and its evolution in these flies. Positive selection studies across these loci reveal episodes of positive selection on branches leading to specialists. In vitro and in vivo assays are underway that aim to study the function of specific amino-acid substitutions within homologous genes encoding these detoxification enzymes in relation to the detoxification of mustard oils (see figure to the right.) Crystallography studies with collaborator Dr. William Monfort at the University of Arizona facilitate identification of structurally important amino acid changes within and among species. This work is conducted by Tim Rast and Andrew Gloss (Ph.D. student). Questions relating to the evolution of the upstream signaling pathway--the loci involved in regulation of the detoxification genes and how natural selection has shaped them, will be pursued by incoming PERT postdoctoral fellows Anna Nelson Dittrich.
Evolution of host specificity--II. Comparative neurobiology and behavioral genetics
Most parasites specialize on a limited set of hosts. What is the neurological basis for this? How does the peripheral and central nervous system change as species become specialized or switch hosts? The Drosophila and Scaptomyza lineages are well suited to such studies because they contain leafmining as well as free-living species, and within the leafmining species is includes those such as S. flava, which feeds on most plants in the mustard family, as well as S. nigrita which feeds only on a single mustard species. Moreover, some Drosophila and generalists and others specialists, and many have completely sequenced genomes, enabling a complete understanding of the genomic landscape underpinning these adaptations.
One part of this project uses comparative approach to study how the Drosophila antennal lobe has evolved in the context of host specialization. We are dissecting the neuroanatomical and chemosensory adaptations that underpin host-specificity in the lineage Drosophila, with a focus on the Scaptomyza radiation (Benjamin Goldman-Huertas, Ph.D. student). This is in collaboration with Dr. Lynne Oland and Dr. John Hildebrand in the Department of Neuroscience. We are also identifying the host plant compounds necessary for host plant finding and the chemosensory loci underlying these adaptations.
One part of this project uses comparative approach to study how the Drosophila antennal lobe has evolved in the context of host specialization. We are dissecting the neuroanatomical and chemosensory adaptations that underpin host-specificity in the lineage Drosophila, with a focus on the Scaptomyza radiation (Benjamin Goldman-Huertas, Ph.D. student). This is in collaboration with Dr. Lynne Oland and Dr. John Hildebrand in the Department of Neuroscience. We are also identifying the host plant compounds necessary for host plant finding and the chemosensory loci underlying these adaptations.
