Research
Developmental genetics of Heliconius wing patterns
Neotropical Heliconius butterflies are famous for their wing pattern polymorphism and mimicry. There is an active community of researchers working on many aspects of Heliconius biology, including population dynamics, behavior, phylogeny, genetics, and development. The experimental accessibility of this genus at many levels provides an exciting opportunity to produce a highly integrated portrait of the interplay between speciation and morphological evolution. Heliconius is rapidly maturing as a key model system for evolutionary studies, and resources such as linkage maps, transcriptome sequences, whole genome sequences, and stock centers for Heliconius melpomene and Heliconius erato are available.
We are working closely with the McMillan Lab at the Smithsonian Tropical Research Institute to positionally clone adaptive color pattern genes from the species H. erato. This work is being done in the context of a larger international collaboration to identify color pattern genes across multilple species of Heliconius.
Developmental variation in populations
A growing body of data shows that development can be robust to variation in parameters such as the timing or level of gene expression. This leads to the prediction that natural populations should be able to host developmental variation that has few obvious phenotypic effects. Cryptic variation is especially interesting to evolutionary biologists because it can result in selectable phenotypes when “released” by environmental or genetic factors. Currently, however, we have little idea of how variation is distributed between genes or over time in pattern formation processes. We are approaching this issue by studying how wing pattern formation can vary within the buckeye butterfly species Junonia coenia. In addition to surveying patterns of gene regulation over time, we arealso developing a conceptual framework and analytical tools to make use of large data sets of spatial gene expression patterns.
Regulation of wing pigment genes
Many of the colors we perceive in butterfly wings are due to pigments. Several classes of pigments are found in butterfly wings including melanins, pterins, papiliochromes, and ommochromes. Our current work is focused primarily on the ommochrome pigments - tryptophan-derived molecules that typically appear orange or red. Ommochromes are utilized throughout the insects as eye pigments, but have gained a novel function in wing coloration in brush-footed butterflies (Nymphalidae). These pigments provide a nice model for exploring how a complex biochemical process may be redeployed during evolution in a novel developmental context. We are studying the regulation of genes encoding transporters and enzymes required for ommochrome synthesis, and working to determine how the regulation of ommochrome genes is modulated by adaptive color pattern "switch genes" in polymorphic Heliconius butterflies.
Notch signaling in butterfly wing pattern development
Across the animal kingdom, the Notch signaling pathway is a fundamental component of pattern formation in many different contexts. Notch is a membrane-bound receptor molecule, and through interactions with ligands and other factors Notch is able to facilitate the formation of complex patterns during development. Previous gene expression studies in butterfly wings have implicated Notch in several pattern formation processes, including early eyespot determination and the arrangement of scale cells into spaced rows. We are also beginning to explore the role of Notch in determining butterfly wing shape.
