There exists an astonishing diversity of organismal forms in nature, from butterfly wings to bird beaks, from kelp fronds to angiosperm flowers. The problem of understanding the origin and evolution of these “endless forms” can be decomposed into three essential components: (i) the genetic basis that prescribes phenotypic variation; (ii) the developmental process through which gene products change phenotypes; and, (iii) the ecological consequence (or adaptive significance) of alternative phenotypes in their natural habitat. We aim to achieve such a "functional synthesis" between genetics, development, and ecology to understand phenotypic evolution using monkeyflowers
(Mimulus) as our main study system.
The genus Mimulus contains 160-200 species that exhibit tremendous natural variation in flower morphology (Figure 1 on the right), and has been the subject of intensive ecological and evolutionary studies for over 80 years. Of particular interest to us is a pair of sister species that are genetically very similar (>99% identical in coding regions of the genome) but display dramatically different flower phenotypes (highlighted by the red box in Figure 1). The bumblebee pollinated M. lewisii has pale pink flowers with broad, flat petals and contrasting yellow nectar guides. The hummingbird pollinated M. cardinalis has red flowers with reflexed petals that form a tubular corolla. Although the two species are interfertile with hand pollination, they rarely hybridize in wild sympatric populations due to pollinator preference.
These two species have several features that greatly facilitate genetic analysis, including high fecundity (~1000 seeds per fruit), short generation time (~3 months), and small genome size (~500 MB). Also available in this system are sophisticated genomic and functional tools, largely developed in Dr. Toby Bradshaw's lab at the University of Washington. The short-read-based genome assemblies of M. lewisii and M. cardinalis, in conjunction with community resources developed for their congener, M. guttatus, have enabled rapid gene identification through positional cloning and bulk segregant analysis. The in planta transformation system for M. lewisii has permitted rigorous characterization of gene function and developmental processes by transgenic experiments. The EMS-induced floral mutants of M. lewisii ( Figure 2 ) have furnished the raw materials to study the developmental genetics of many ecologically important floral traits (e.g., carotenoid pigmentation, corolla tube formation and elaboration, nectar volume, pistil length) that are difficult to study using other model systems.
The major questions we address in this lab include: What are the genes underlying the dazzling floral variation in Mimulus and in other angiosperms? Does evolution prefer certain “hot spot” genes to generate similar flower phenotypes recurrently in different plant lineages? Are the causal mutations more likely located in coding DNA or cis-regulatory regions? What is the nature of the causal mutations? Are they simple nucleotide substitutions, small insertions or deletions, or relatively large insertions or deletions (perhaps generated by historical activity of transposable elements)? How do these gene products (e.g., transcription factors, enzymes, signaling proteins) regulate the production, transportation, modification, and degradation of pigments to generate floral color patterns? How do they regulate the division, elongation, and polarization of cells to make flower shapes? What is the adaptive significance of the diverse floral forms? How do flowers with different color patterns and shapes interact with different pollinators? What role do these interactions play in adaptation, reproductive isolation, and speciation? For more details, please see our specific research projects.