Evolutionary developmental (evo-devo) studies seek to understand the molecular and developmental basis of morphological change. Such studies focus primarily on macroevolutionary problems by comparing fixed developmental patterns across broad phylogenetic distances, usually between model organisms such as Arabidopsis and Antirrhinum. However, a recent NSF workshop recognized the need to begin to integrate development and microevolution (2005). Limited work in this area has demonstrated that microevolutionary processes (selection) contribute to population level differences in gene expression and protein function, which have major consequences in the evolution and development of morphology (Fondon and Garner, 2004; Shapiro et al., 2004; Moczek, 2006). These research programs serve to highlight the importance, power, and paucity of microevolutionary developmental studies. I propose to examine the relationship between morphological and molecular developmental variation in Mimulus guttatus shoot architecture and microevolutionary processes in M. guttatus.
As Goethe first posited in 1790, the plant shoot is composed of only two vegetative organ types: leaf and stem. This seemingly simple body plan is reiterated and modified over the course of evolution to construct an amazing amount of morphological diversity in shoot architecture. Much of this diversity in plant form is dictated by the location, frequency, and timing of branch outgrowth (Bell, 1991; Barthelemy and Caraglio, 2007). These same developmental processes also contribute to variation in shoot architecture within species, where they have the potential to influence fitness. The development of branches affects leaf placement, light interception, and ultimately determines the number of meristems available for sexual (Geber, 1990; Lortie and Aarssen, 1997, 2000a) and asexual (Watson, 1984) reproduction. Therefore, the developmental dynamics of plant architecture should be subject to selection (Lortie and Aarssen, 1997, 2000b)}, making it an excellent system for giving insight into morphological and functional divergence of natural populations.
Multiple attributes of Mimulus guttatus (monkeyflower) make it ideal for delving into the microevolution and development of shoot architecture. Natural populations of M. guttatus have dramatic differences in shoot architecture. For example, in Oregon, individuals from the coastal dunes are relatively highly branched while individuals from the Cascades have fewer branches (Hall and Willis, 2006). Maximum fitness for plants from each location is achieved in its native environment, indicating that M. guttatus shoot architecture may be adaptive and under selection (Hall and Willis, 2006). M. guttatus is also amenable to molecular analysis and is easily propagated in greenhouses. An ongoing genome project undertaken by the Joint Genome Institute (JGI) in conjunction with the Willis lab (at Duke University, funded by an NSF FIBR grant, 2003-2008) is providing a wealth of M. guttatus sequence data.
This proposed research will give insight into how plant development evolves in the context of populations that have diverged in response to environmental change. In order to understand the recent divergence of two natural populations, I will integrate data from multiple levels including DNA sequences, gene expression patterns and the resulting developmental phenotypes, and eventually fitness consequences of shoot architecture, a morphologically and functionally important character. Additionally, my dissertation is designed to facilitate cross-taxa comparisons. It will add an important fourth eudicot species for which we will have detailed knowledge of shoot architecture developmental genetics.