P. Roxanne Steele (Roxi)
University of Texas at Austin, Plant Biology Graduate Program, 4th year doctoral candidate
An Adventure in Tropical Botany
It is not every day that a mechanical engineer turns botanist, but it is with great enthusiasm that I am pursuing a Ph.D. in Plant Biology at The University of Texas at Austin. Because I love to both learn and teach, I transformed my interest in nature and science from a hobby into a life-long pursuit of gaining knowledge about the natural world and sharing it with others. I intend to continue this pursuit after I complete my doctoral research by teaching and creating educational materials.
Although I never disliked engineering, I always felt something was just not right. Not long after graduating I began exploring alternate ideas for a career. Over several years I contemplated many different paths such as engineering management, architecture, nature photography, and technical writing. I was working as an engineer, but my free time was spent in the garden, exploring nature, or taking vacations that gave me the opportunity to experience various ecosystems around the world. One summer I took a college class called “Race to Save the Planet”, a course that taught about many environmental issues around the world and about positive programs in place for addressing the problems. I wondered how I could contribute. It was not until I volunteered for an Earthwatch program where I spent two weeks helping scientists in a Costa Rican rainforest that it struck me – I wanted to contribute to the conservation of the world’s ecosystems by studying plants in the rainforest and sharing that education with other scientists and policy makers.
Without delay I quit my engineering job, moved to a rural town where the cost of living was manageable, began working in a greenhouse, and began taking college botany courses; I have never looked back. The first course was Plant Taxonomy. I loved it! It combined my love of plants with an analytical process for identifying, describing, and classifying organisms. Supported by my bachelor’s degree in science, and after taking several undergraduate botany courses leading to an Associates of Science in Biology, I applied to a Plant Biology Ph.D. program at the University of Texas at Austin. I am now a 4th-year doctoral candidate, nearing the accomplishment of a Ph.D.
I began reading scientific literature to identify a plant group in the New World tropics that was lacking information about plant relationships and biogeographic histories. I wanted my research results to contribute to the scientific community by including both modern techniques using molecular data to discover the evolutionary relationships between organisms (phylogenetics) and more classical practices of investigating and describing the morphological (physical) characteristics of plants (taxonomy). These two areas of study (phylogenetics and taxonomy) are often lumped together and called systematics. I wanted to find a group of plants about which I could study both systematics and biogeography. It was only after eight months of researching the literature that I found the perfect group of plants to study – Psiguria (pronounced si-gur-ee-uh), a small genus of vines in the cucumber family (Cucurbitaceae) that grows only in the Neotropics (Central and South America and the Caribbean).
Psiguria stood out among all other groups of plants for several reasons. First, the taxonomy had not been addressed since 1916 when the genus was called Anguria. In 1962, one author noted that this name was not historically correct according to naming guidelines. In 1978, another researcher believed that the 29 species described in 1916 were not truly separate species; he believed there were only eight. However, several authors since then have argued that there are more than eight species. Currently, there are 17 species of Psiguria recognized by the International Plant Names Index, but the debate about delineation between species continues.
This controversy stems from the fact that many Psiguria plants change flower color and leaf shape dramatically over their lives, and they all switch sex from male to female when stem diameter grows to a particular size. Scientific names have been published based on dried specimens that represent only a portion or a life stage of the plant, leading to multiple classifications of the same species. I intend to clear up this confusion and update the archives using both molecular and morphological characteristics.
Second, Psiguria has incredibly interesting ecological and life history features. The plants have flowers and fruits that are important to insects, birds, and mammals of rainforest ecosystems. Moreover, it has a mutualistic (positive, symbiotic) association with its pollinators, Heliconius butterflies, making it a model system for investigating coevolutionary relationships. Unlike most butterfly species that take in necessary egg-laying nutrients while eating leaves during their caterpillar life stage, as adults, Heliconius butterflies obtain these nutrients from the pollen of Psiguria flowers. The historical relationship between Heliconius and Psiguria has influenced both the reproductive strategy of the butterflies and, potentially, the separation of Psiguria as a genus distinctive from others in its subtribe. Since the evolutionary history of Heliconius butterflies has already been estimated by other researchers, a phylogeny of Psiguria is the only missing information needed to fully investigate the evolutionary significance of this system.
Third, Psiguria has a model pattern of geographic distribution with two endemic species on Caribbean islands. The possible migration patterns of species occurring both on continents and islands are constantly debated in the literature, particularly in the geologically complex West Indies. Phylogenetic histories of organisms can be used to infer where the genus originated and how many times and in which direction it moved between Central and South America and the Caribbean islands. I will use the phylogeny of Psiguria that is reconstructed from molecular and morphological data sets, along with two other computer programs to estimate its biogeographic history.
Fourth, Psiguria is a small enough group that I can both write a complete monograph of the genus and reconstruct its phylogenetic history using several types of data. The monograph (a highly detailed and thoroughly documented study written about a limited area of a subject or field of inquiry) of Psiguria will include: 1) the biogeographic range of all species with maps showing locations where specimens have been collected, 2) a description of each species based on the observation, comparison, and measurements of plants in the field and in greenhouses and of over 900 specimens borrowed from five distinguished herbaria around the country, 3) a key to species (a list of the significant characteristics of the members of a group of organisms to facilitate identification and comparison), 4) phylogeny of the genus along with estimated sister relationships, 5) descriptions of pollen with SEM (scanning electron microscopy) photographs, and 6) chromosome counts, which have never been conducted in Psiguria or any of its closest relatives.
A phylogenetic history is a diagram that shows which species are most closely related to each other, like a family tree except the ancestors are unknown. An understanding of historical relationships is important to ecologists studying the interactions between various organisms, and to conservation biologists who often (sadly) have to make decisions about which species to save from extinction, and they want to include a variety of distinctly unrelated groups. A clear phylogeny of Psiguria can be combined with other flowering plant phylogenies to determine broader relationships between groups.
A well-supported phylogeny must be estimated from a combination of multiple data sets because each type of data has limitations. The data sets include morphological characteristics and DNA sequences from two different locations in the plant cell (nucleus and chloroplast). I compile data from all species of Psiguria, and then make comparisons to determine which species are more closely related to each other. Gathering this information means that I spend my time in three different settings: 1) in the herbarium measuring, comparing, and contrasting my collections as well as the 900 borrowed specimens mentioned above, 2) in the field collecting and studying live plants, and 3) in the lab and on the computer estimating species relationships based on DNA sequences.
Field trips to collect Psiguria are the most exciting and the most educational portion of my work. Informative plant descriptions written for both the scientist and the amateur plant enthusiast depend on the author having intimate knowledge and experience with the plants in their natural habitats. Additionally, fresh leaves provide the best material for molecular studies.
In the last two years, I have traveled to Costa Rica, Puerto Rico, and the Dominican Republic to collect plants, where I collected five species of Psiguria. Psiguria is not like a roadside weed that grows in many places. It specifically grows in mid-elevation rainforests over other vegetation or up into canopy trees. Individuals may be hundreds of meters apart; therefore, finding them entails researching the general locations where Psiguria has been collected in the last 20-30 years, making a map of these locations, and driving/hiking around searching the areas for them. But, since there is no guarantee that I will actually find these plants in the field, lab work is supplemented with leaf material sampled from herbarium specimens.
Outside of these infrequent collecting trips, I spend the majority of my time in the lab, extracting chemical information (DNA sequences) from the plants. Though arguably a more reliable source for determining plant relationships than subjective physical features, molecular information is often much more difficult to obtain.
The genus Psiguria is considered a relatively young group of plants – less than 19 million years old. As a result, it is very difficult to find differences between DNA sequences that have evolved in this short time. Yet, differences are the source of determining relationships between species. Since it is not yet feasible to sequence entire genomes for all organisms (it has been done for only a handful of model organisms such as human, mouse, and rice), systematists must find regions of the genome that are informative (we call them markers).
This is not a simple process. The same markers are often not useful over a broad range of plant groups; therefore, discovering informative markers for each study is a tedious process involving an exhaustive search through the genome. I spent nearly a year identifying markers in the chloroplast genome – a test of 25 regions resulted in only eight informative markers. I spent another year screening 144 regions in the nuclear genome, resulting in only three markers that were phylogenetically informative for Psiguria. At the same time, I tested these 144 regions in other plant groups and recently submitted the results for publication.
To compare DNA sequences and search for differences and similarities, I use a variety of computer programs to analyze the data. Over the last 3½ years, I have extracted DNA from 11 of the 17 species of Psiguria, completed the identification of chloroplast and nuclear markers, begun biogeographic analyses, and begun listing, measuring, and databasing morphological data. The remaining tasks include finalizing data collection and analyses and preparing my dissertation.
My Graduate Experience, Teaching Experience, and Short-term and Long-term Career Goals
I realized many years ago when I taught Junior Achievement in a 5th-grade classroom and I volunteered as an after-school tutor of inner city youth (4th-grade), that I loved being a role model and inspiring young minds to think. I particularly enjoyed the challenge when students were having difficulty with the material but had strong desires to understand. I loved struggling through the problem with them, and then seeing the “a-ha” moment when understanding finally came. It was through those experiences that I was determined to always have a teaching component in my life.
My first three years as a graduate student, I was a teaching assistant for the Native Plants of Central Texas class. Unlike many teaching assistant positions, this one allowed me to take nearly complete responsibility for the lab portion of the class – lab and activity preparation, student engagement, instruction, and assessment. Each week I took 16 students on field trips to parks, preserves, and botanical centers around Austin, TX, where they learned the scientific names for 15 local plants. The experience was awesome! The class was designed for students, who were not biology majors. Many of them admitted to me at the beginning of each semester that they were only taking the class because they needed four credits in science, and they did not really care about plants. I never held that against them; I just smiled and considered it a challenge to get them interested, even in a small way. I do not think I ever ended a semester without feeling that I met that challenge. I showed them that walking or hiking through the forest could be much more interesting if they knew the plants they were passing and an interesting fact about each one. I am certain that my enthusiasm for nature and plants excited the students, and encouraged many of them to appreciate the plants around them more than they had when they first walked into the classroom.
In the current (2007-2008) school year I have a new teaching assignment. I was awarded a teaching fellowship, funded by the National Science Foundation and called GK-12, by the Environmental Science Institute at The University of Texas at Austin. This program teams up graduate students in science with middle-school science teachers to enhance the middle-school students’ experiences in science, and to show them how classroom science tasks are applied to real-world projects. This program also gives graduate students the opportunity to sharpen their communication skills and their abilities to explain difficult concepts. So far, I have had great experiences in the classroom. I predominantly work with 7th-grade students. My goals are similar to those I had with the Native Plants class and the goals I have for the rest of my career: to open up students’ minds and eyes to nature such that they see more than just green walls and brown fields when they drive down the road; they see active natural systems that are both incredibly interesting and incredibly important to our lives.
In addition to teaching assignments, I have also been training an undergraduate student in our lab would like to pursue a graduate degree in molecular biology. I am teaching her lab processes necessary to my research, which she can carry over to her own research. In return, she is helping me to complete the lab portion of my research.
My short-term goal is to complete my doctoral dissertation. This entails collecting specimens during my final field trip to Bolivia and Perú, databasing approximately 40 measurements from multiple specimens of Psiguria in the herbarium, completing computer analyses of the various data sets, and writing my dissertation. After completing of my PhD, I hope to work as a professor at a teaching university or an educator at a botanical garden, where I can continue to educate and continue to learn. Specifically, my long-term goals include not only enhancing my own knowledge of ecosystems, but also educating students and the public about the natural world and our impact on it. I want to stress the connection we have with nature and our responsibility to learn about it and preserve it for future generations. At the same time, I would like to create educational materials about plants that will be useful not only to scientists, but also to the general public.