Research Interests

Organisms are the objects of natural selection.  Organismal function determines the success or failure of an individual: survival, growth, and reproductive output.  My research examines how plant physiological function influences plant survival and performance.  I am particularly interested in the diversity of form apparent throughout the plant bauplan and I try to understand the relationship between form and function in this broadest of senses.

I like to cross the boundaries of academic subfields to better understand the relationships between plants and their environment.  I employ a variety of methods, including field studies, traditional ecophysiological measurements, stable isotopes, high resolution anatomical imaging, and, because most of my work is framed in an evolutionary context, phylogenetic comparative methods.  I often modify existing equipment and design and develop new equipment to address my questions.  Working across disciplines also means that I actively collaborate with people in other fields, including biogeochemistry, genomics, conservation biology, and anthropology.  Despite this breadth of interests, my core interests in the relationships between morphology and physiology are expressed in two systems.

First, the main focus of my research is the physiology and evolution of flowers, the most beautiful of plant structures, over macroevolutionary timescales.  Nowadays there is no question that flowers play a critical role in reproduction, but this idea was heretical when it was proposed by Köhlreuter and Sprengel in the mid- to late 1700s.  Since then, our understanding of the diversity and complexity of flowers has been based primarily on the role of pollinators in shaping floral form.  Yet, floral structures experience the same physiological constraints as other plant structures, though we know little about the physiological processes involved in producing and maintaining them.  The incredible (and, often, bizarre) morphologies of many flowers may be enabled by novel physiological strategies and constrained by the fundamental necessity of resource supply.  Physiological traits may both promote and inhibit selection by pollinators.  My research elucidates the mechanisms of water transport to flowers and examines the macroevolutionary patterns of floral physiological variation.

Second, closely related species can often differ dramatically in morphology and physiology.  One particularly notable, textbook example of this is the genus Encelia (Asteraceae), which evolved within the last five million years and rapidly radiated throughout North American deserts.  Encelia species vary dramatically, particularly in leaf morphology, reflecting the different climate niches they occupy.  In fact, this genus has been a textbook example of differences in leaf structure and function.  Perhaps even more interesting, wherever Encelia species come into contact, they readily hybridize and produce fertile offspring with intermediate traits.  My work studying the physiology of Encelia is possible thanks only to a broad network of collaborators, particularly Chris DiVittorio (UC-MEXUS) and Sonal Singhal (University of Michigan).  Our focus has been on two species, E. palmeri and E. ventorum, a desert and a dune native, respectively, which come into contact along the central coast of Baja Mexico.  We have combined reciprocal transplants with ecophysiological phenotyping and genomic analyses of gene flow to characterize the earliest steps of speciation.  We are broadening these studies to encompass the entire genus in order to comprehensively characterize the rapid evolution of morphological and physiological trait variation.