POSTDOCTORAL RESEARCHER
	Curriculum Vitae
	Email: tculley@uci.edu

Research Interests

My research is mainly concerned with the evolution of plant breeding systems and involves both ecological and genetic approaches. Specifically, I am interested in what factors influence the expression of particular breeding systems and how these systems change over time in response to environmental factors. My research is composed of two main themes: the evolution and expression of cleistogamy in violets (Viola) and the evolution of dioecy in the Hawaiian genus, Schiedea.

Many Viola species have mixed mating systems because they produce both open, chasmogamous (CH) flowers and closed, cleistogamous (CL) flowers on the same individual. CH flowers are often assumed to be outcross-pollinated while CL flowers are automatically self-pollinated. The main purpose of my research in Viola is to determine why these two very different types of flowers are produced. Most of my work has focused on two violet species found in the northeastern United States, Viola pubescens and V. canadensis. Contrary to the assumption that showy CH flowers are primarily outcross-pollinated, I found that CH flowers exhibit delayed selfing, and are capable of variable and sometimes quite high levels of selfing (s = 0.07-0.60). In addition, a low level of inbreeding depression (0.10) expressed in CH flowers is consistent with a highly selfing species. During field research conducted in an Ohio population of V. pubescens over several years, I found that CH flowers were responsible for a larger portion of overall seed production than CL flowers. In general, it appears that the dual system of chasmogamy and cleistogamy in Viola is a means of adapting to unpredictable pollinators in the early spring (through outcrossing of CH flowers when pollinators are present and delayed selfing in CH flowers when pollinators are absent) and to a lack of pollinators during the rest of the season (through CL flowers). In addition, energetic costs may be important because costly CH flowers are produced in the early spring when light availability is highest and the potential for photosynthesis is greatest, while reduced CL flowers appear in the shaded understory after the forest canopy forms.

Breeding system evolution is also the subject of research with Schiedea, a genus that has undergone extensive radiation in the Hawaiian Islands and contains a full range of breeding systems - including hermaphroditism, gynodioecy (co-occurrence of females and hermaphrodites), and dioecy (co-occurrence of females and males). My current postdoctoral research with Schiedea is a quantitative genetics experiment with Drs. Stephen Weller, Ann Sakai, and Diane Campbell. We are currently conducting an artificial selection project to study the genetic potential for sex allocation shifts to male and female function in two gynodioecious species, Schiedea salicaria and S. adamantis. The sex allocation hypothesis suggests that dioecy evolves in a gynodioecious population following greater allocation to male function in hermaphrodites and greater female function in females. We are testing this hypothesis by artificially selecting for increased male function in hermaphrodites (measured by stamen biomass) and increased female function in females (measured by carpel and fruit biomass) over several generations. To initially predict the response to our selection program, we are using half-sib paternal families to estimate the additive genetic variances of the sex allocation traits and their genetic covariances with other reproductive characters. Preliminary evidence suggests that many traits associated with increased male and female function have a heritable basis and thus may contribute directly to the evolution of dioecy. In a related project, we are also measuring the quantitative genetics of ecophysiological traits using the same plants from the half-sib families. This is of particular importance because the heritability of ecophysiological traits have rarely been measured on the scale of our current study.

I am also interested in the genetic consequences of specific plant mating systems, as measured with different molecular techniques. Together with Andrea Wolfe at The Ohio State University, I measured the genetic structure in six populations of Viola pubescens, using isozymes and a relatively new molecular marker known as inter-simple sequence repeats (ISSRs). Both markers gave similar results, showing considerable genetic variation in the species, along with moderate population substructuring. This is consistent with the mating system of the species, in which selfing through CL (and CH) flowers contributes to population differentiation, and outcrossing through CH flowers increases variation and gene flow among populations. Related to my genetics work, I recently completed a study investigating two different methods of calculating Gst, the measure of population differentiation.

My genetic research has also led to an interest in the genetic effects of habitat fragmentation. Fragmentation of natural areas often results in a decrease in population-level genetic variation as well increased genetic differentiation. This topic is of particular importance in the temperate deciduous forest in North America because of widespread deforestation that has occurred over the past two centuries. Ohio is one region that has been greatly affected as the amount of forested land in the state declined from 95% in the early 1700's to 10% by 1910. Today, approximately 31% of land in Ohio is forested. This pattern of deforestation in Ohio has created many agricultural woodlots, in which plant populations are forced to persist. I am currently collaborating with Thomas Grubb Jr. on a study on Viola pubescens examining the genetic effects of habitat fragmentation in the temperate deciduous forest. Preliminary evidence suggests that the species has indeed been negatively affected by fragmentation; genetic variation was lowest in populations found in the smallest woodlots, while those in larger woodlots were genetically variable. Genetic differentiation among populations was also detected (theta = 0.27), but did not indicate a completely selfing species. This is consistent with the CH/CL breeding system of this species because selfing through CH and CL flowers may reduce genetic variation and promote differentiation, but occasional outcrossing through CH flowers may prevent populations from becoming completely differentiated from one another. Small populations of Viola pubescens in Ohio are still in danger of extinction if they do not contain enough genetic variation to adapt to changing environments.

Publications:

Culley, T.M., S.G. Weller, and A.K. Sakai. In press. The evolution of wind pollination in angiosperms. Trends in Ecology and Evolution.

Cummings, C.L., H.M. Alexander, A.A. Snow, L.H. Rieseberg, M. Kim, and T.M. Culley. In press. Fecundity selection in an experimental sunflower crop-wild system: how well do ecological data predict crop allele persistence? Ecological Applications.

Culley, T.M., L.E. Wallace, K. Gengler-Nowak, and D.J. Crawford. 2002. A comparison of two methods of calculating G_st, a genetic measure of population differentiation. American Journal of Botany 89(3): 460-465.

Culley, T.M. 2002. Reproductive biology and delayed selfing in Viola pubescens (Violaceae), an understory herb with chasmogamous and cleistogamous flowers.  International Journal of Plant Sciences 163(1): 113-122.

Culley, T.M., and A.D. Wolfe. 2001. Population genetic structure of the cleistogamous plant species Viola pubescens, as indicated by allozyme and ISSR molecular markers. Heredity 86(5): 545-556.

Snow, A.A., K.L. Uthus, and T.M.Culley. 2001. Fitness of hybrids between cultivated Raphanus sativus and weedy R. raphanistrum: implications for weed evolution. Ecological Applications 11(3): 934-943.

Culley, T.M. 2000. Inbreeding depression and floral type differences in Viola canadensis (Violaceae), a perennial herb with chasmogamous and cleistogamous flowers.  Canadian Journal of Botany 78(11): 1420-1429.

Culley, T.M., S.G. Weller, A.K. Sakai, and A.E. Rankin. 1999. Inbreeding depression and selfing rates in a self-compatible hermaphroditic species, Schiedea membranacea (Caryophyllaceae).  American Journal of Botany 86: 980-987.

Last Updated:  July 9, 2002