Current research projects

My research is in the field of evolutionary ecology, particularly the ecology and evolution of reproductive strategies in flowering plants. There are over 250,000 described species of flowering plants and much of this diversity involves variation in reproductive strategies. In particular, most flowering plant species (ca. 75%) are hermaphroditic, that is, flowers have both stamens that produce pollen grains (male function) and a pistil that contains ovules to be fertilized (female function). However, in the remaining (ca. 25%) species, flowers or plants exhibit some form of gender specialization. For example, monoecious plants allocate to both male and female functions, but the sexual functions are spatially separated into male and female flowers. In contrast, dioecious species have separate genders in the form of male and female plants. A female plant would have flowers with a pistil but no stamens, and the opposite would be true for a male plant. Even within hermaphroditic species, individual plants can differ dramatically in their allocation to female versus male function. I'm particularly interested in:

1) Understanding what factors determine the allocation of resources to male function (pollen number and size, nectar and petals that attract pollinators and thus lead to the dispersal of pollen to other flowers) as opposed to female function (ovule number, seed number and size). Theoretical models, known collectively as sex allocation theory, make predictions about gender allocation patterns in flowering plants. However, there have been few empirical tests of the assumptions and predictions of these models. In collaboration with Dr. S. Mazer at UCSB, we are examining the environmental and genetic sources of variation in gender expression in sister species of the genus Clarkia (Onagraceae).

2) Understanding how breeding systems (inbreeding versus outcrossing) and plant-pollinator interactions affect gender allocation patterns. Selfing (mating with self in hermaphroditic individuals) has both costs and benefits. The most obvious cost is the expression of lethal or harmful recessive alleles (i.e., inbreeding depression). The most obvious benefit is the ability to reproduce when pollinators or mates are scarce (i.e., the reproductive assurance hypothesis). Selfing has evolved repeatedly in flowering plants and I'm interested in understanding what factors favor the evolution or maintenance of selfing and how selfing affects sex allocation strategies.

3) Understanding how phylogenetic (i.e., historical) and developmental constraints affect plant reproductive strategies. In some plant families like the Cucurbitaceae (the cucumber and squash family), there is a definite architecture associated with flower production. For example, in many cultivated cucurbits, male flowers are produced first along the main branch, while female flowers are produced either at later nodes or on secondary branches. If such patterns reflect phylogenetic or developmental constraints on sex expression, they must influence gender allocation. How important are these constraints? Few studies of wild species have addressed this question.

4) Developing resource management plans for a local nature preserve. Understaffed and underfinanced, small nature preserves face numerous issues related to resource management. With the support of a National Science Foundation grant, I am mentoring a number of projects that focus on forest regeneration and control of invasive species.

REU Program

Current Grants