Theresa M. Culley

	Theresa M. Culley Assistant Professor Ph.D, The Ohio State University Plant Biology

Address: Theresa M. Culley Department of Biological Sciences, ML006 614 Rieveschl Hall University of Cincinnati Cincinnati, Ohio 45221-0006, USA	Telephone: (513) 556-9705 FAX: (513) 556-5299 Email: theresa.culley@uc.edu
Office/Lab Location: 724 Rieveschl Hall [Note that we have moved from our old lab in room 816]

In my lab, we are interested in the evolution of plant breeding systems and the interplay between the reproductive biology of a species (its pollination biology, seed production, susceptibility to herbivory, etc.) and population genetics. I incorporate both ecological and genetic approaches in my research because they both yield valuable insights into evolutionary questions. My current research interests can be separated into the following:

The Evolution of Invasiveness in the Callery Pear (Pyrus calleryana)

The Callery Pear (Pyrus calleryana) was originally introduced into the United States from China in the early 1900's as a rootstock species and as a source for fireblight resistance. It has quickly become one of the most popular ornamental tree species planted in urban areas. Known as the 'Bradford', 'Aristocrat', 'Cleveland Select', etc. (see list), these cultivars are highly desired for their springtime display of white showy flowers, vibrant fall leaf color, and tolerance of excessive drought and pollution. Within the last decade however, wild Pyrus calleryana have begun appearing and multiplying in natural areas, especially disturbed sites along railroads, roads, and along park boundaries. Furthermore, many cultivated Callery Pears in urban yards have also begun producing fruits even though each cultivar is self-incompatible. Many of these fruits are dispersed by introduced birds such as starlings. In our lab, we are studying why Pyrus calleryana is suddenly beginning to spread and becoming invasive. Based on a combination of ecological and genetic studies, it now appears that the recent expansion of Callery pear cultivars in some localities is due to intraspecific hybridization between the widespread 'Bradford' cultivar and other newer cultivars. This has been verified by hand-pollinations conducted in the greenhouse between different cultivars and also through genetic analyses with microsatellite markers specific for each cultivar. We are continuing to study this intriguing species to understand the factors that contribute to the evolution of invasiveness in an introduced species as well as to develop practical suggestions for the prevention of its continuing spread within the United States.

Interested in Invasive Plants? Check out the resources at the Ohio Invasive Plants Council (OIPC) webpage. This is a great organization for gathering information, making contacts, and learning what you can do to reduce the impact of invasive plants in our environment.

The Evolution and Expression of Cleistogamy in Violets (Viola)

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. One purpose of my research in Viola is to determine why these two very different types of flowers are produced, using 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, CH flowers exhibit delayed selfing and are capable of variable 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 selfing species. CH flowers also appear to be responsible for a larger portion of 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, while reduced CL flowers appear in the shaded understory after the forest canopy forms. Read More...

Genetic and Ecological Effects of Habitat Fragmentation

Fragmentation of natural areas may result 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 has created many agricultural woodlots, in which plant populations are forced to persist. I have collaborated with Thomas Grubb Jr. on a study of Viola pubescens examining the genetic effects of habitat fragmentation. Evidence now 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 (Fst = 0.27), and is consistent with the CH/CL breeding system. 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. I am currently conducting a similar study in southwestern Ohio using urban populations of V. pubescens to better understand how habitat fragmentation induced by urbanization might affect this species.

Population Genetics and Plant Mating Systems

I am also interested in the genetic consequences of plant mating systems, as measured with different molecular techniques. Together with Andrea Wolfe at The Ohio State University, we quantified the genetic structure in six populations of Viola pubescens using isozymes and inter-simple sequence repeats (ISSRs). Both markers showed considerable genetic variation 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. I have recently developed microsatellite markers for V. pubescens and am currently comparing the genetic results generated by microsatellites, isozymes, and ISSR makers.

For protocols of all types used in my lab, see the Protocol Page...

The Evolution of Dioecy in the Hawaiian Genus Schiedea.

Breeding system evolution is also the subject of my 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). I am currently working with Drs. Stephen Weller, Ann Sakai, and Diane Campbell on a quantitative genetics experiment in which we are conducting artificial selection to study the genetic potential for sex allocation shifts to male and female function in two gynodioecious species, Schiedea salicaria and S. adamantis. Many traits associated with increased male and female function have a heritable basis and thus may contribute directly to the evolution of dioecy. In addition, we also measured the quantitative genetics of ecophysiological traits using plants from our initial crossing program for both species. We found that some ecophysiological traits are heritable, but only in certain sexes within different species. This is of particular importance because the heritability of ecophysiological traits have rarely been measured on the scale of our study.