Kelly Dyer, MSc - US grants

How do new species arise? A central goal of evolutionary biology is to understand how new species form and the processes that maintain boundaries between species. This research will investigate whether selection to strengthen reproductive barriers between species may, as a consequence, also initiate reproductive isolation within species. The specific goal of this project is to dissect the genetic basis of female mate preference in the fly Drosophila subquinaria, a species where some females display increased behavioral discrimination both against males of a closely related species as well as against certain males of their own species. Using crossing experiments and genome sequencing technologies, the experiments will ask whether the same genetic regions confer increased mate discrimination within and between species. In addition to advancing our understanding of the genetic basis of behavioral isolation and speciation, this research will also involve the development of genetic resources for the quinaria group of Drosophila, a group that has undergone a recent radiation and has considerable potential as model system for evolutionary, ecological, and behavior genetic studies. This funding will also provide research training in the areas of behavior, genetics, and bioinformatics for a female graduate student as well as for undergraduate and high school students from diverse backgrounds.

In this international collaborative project researchers from U.S. and Canada will perform experiments to study the role of cuticular hydrocarbons (CHC) in species recognition and the maintenance of boundaries between two closely related species of mushroom-feeding flies, Drosophila subquinaria and Drosophila recens. Male contact pheromones consist of a suite of CHCs, and preliminary data suggests that these differ between the two species. Three specific aims will be pursued to test the hypothesis that male CHCs are the key signal traits that are used by females during mate choice and that underlie species discrimination, and that these traits and the female preferences for them have diverged among populations in response to reinforcing selection generated by the presence of the other species. The results of these studies will lay the groundwork for a long-term collaborative research program that will shed light on how behaviors diverge to generate reproductive isolation and ultimately speciation.

Knowledge of the male signals and female preferences will inform hypotheses about whether the genetic basis of within vs. between species female discrimination is the same, and how simple vs. complex we expect these traits to be at the genetic level. The genetic basis of female discrimination and evolutionary genomics of species differentiation in these fly species might be more generally applicable to an understanding of the behavior, ecology, and genetics of reproductive isolation. The data resources will be made available to the community. This project will provide the opportunity to develop a long-term collaboration between early career researchers in the U.S. and Canada and will involve training of students in both laboratories, including women and ethnic minorities. Involvement of junior researchers, especially from groups underrepresented in science, in collaborative international activities is a major goal of OISE.

A central goal of evolutionary biology is to understand both how new species form and the processes that maintain boundaries between species. This study will investigate the evolutionary genetic patterns of the early versus final stages of reproductive isolation in the fly Drosophila subquinaria. Some females of this species display increased behavioral discrimination both against males of a closely related species as well as against certain males of their own species. This research will test whether the ecological processes and genetic mechanisms that reinforce boundaries between different species can result in behavioral isolation among different populations of the same species. The methods will integrate field studies, genetic mapping, and evolutionary genomic approaches.

This funding will integrate research with teaching and learning to provide research opportunities and to develop educational materials that advance the understanding of evolutionary processes at the broader level. Educational activities will translate the focal ideas of the research into inquiry-based classroom exercises that will help students understand why evolution is important in their daily lives through learning about how it operates and the consequences of evolution in action. Graduate students, undergraduates, and high school teachers will be involved in all aspects of the scientific research, curriculum development, and public outreach.

Selfish genetic elements can promote their own transmission into the next generation, even if there is a cost to the inclusive fitness of the host. They are found in all eukaryotes, including, for example, mammals, plants, insects, birds, and fish. A classic example of a selfish genetic element is X-chromosome meiotic drive. 'X-drive' causes males to pass on the driving X chromosome to all of their offspring, which are all daughters. As a result of this biased transmission, theory predicts that X-drive could spread rapidly in a population and potentially drive it to extinction, due to a lack of males. Contrary to this prediction, X-drive is often observed at low to moderate frequencies in nature. The goal of this research is to understand how variation in female mating behavior may counteract the spread of X-drive. The investigators will perform experimental evolution with the fruit fly Drosophila neotestacea to provide new insights into how host behaviors can affect whether X-drive invades into a population, and the frequency at which it is maintained in a population.

The results of this study will deepen our understanding of how X-drive is maintained as a polymorphism in nature, and may be broadly applied to other species. Selfish genetic elements have been proposed for use in pest control regimes for insects that are vectors for devastating diseases. Thus, understanding the dynamics of driving chromosomes in nature may inform pest management practices. Additionally, this project will provide ample opportunities for undergraduate research training.

Unusual adaptations to the environment have long fascinated scientists and the public. There has been much research to understand the evolution of morphological structures (e.g., shape, color, size). However, far less is known about the evolution of novel biochemical adaptations and the impact of these adaptations on the biodiversity of the organisms in which they appear. Of particular interest is how these traits arise if they are costly to the individuals who harbor them. This research investigates the evolution of biochemical adaptations and the genetic and ecological mechanisms that shape them. The research explores the tolerance of insects (fruit flies) to potent toxins in mushrooms that they consume. By investigating the mechanism of toxin tolerance and how this unique adaptation is maintained in this model system, the research will enhance the general understanding of how novel traits emerge and shape biodiversity. This project also includes activities designed to increase public scientific literacy and familiarity with biodiversity by training teachers and students, from middle school to the undergraduate level (particularly from underrepresented minorities), and generating photographic identification guides for insect species associated with mushrooms.

Flies from some groups of Drosophila feed on both toxic and non-toxic mushrooms, and can tolerate high doses of potent cyclopeptide mushroom toxins that are deadly to most other multi-cellular organisms. This research tests hypotheses that predict that: 1) tolerance to these toxic cyclopeptides evolved multiple times; 2) the genetic mechanism of tolerance is not the same in all species; and 3) trade-offs between the physiological costs of tolerance and the benefits of access to a low-competition resource maintain tolerance. The mechanisms of tolerance and their evolution within different fly species are being characterized using metabolomic and transcriptomic analyses that are analyzed in a phylogenetic framework. To assess the genetic basis of variation in toxin tolerance, the researchers are performing artificial selection experiments and genome sequencing. Finally, observational and competition experiments are being used to identify how selective pressures maintain toxin tolerance in natural populations. In sum, this research will provide an in-depth evolutionary, ecological, and physiological assessment of a costly and novel biochemical adaptation, and its impact on biodiversity.

Project Summary/Abstract This proposal is a competitive renewal of a long-standing, successful predoctoral training program whose objective is to broadly train high quality research scientists in basic genetic approaches to the study of biology at the molecular, cellular, organismal, and population level. Funds are requested to increase the number of supported trainees from six to eight each year, reflecting a substantial increase in the number of training grant eligible students. Students in the training program are rigorously trained in cutting-edge genetic and biochemical research and data analysis through laboratory research, general and specialized courses, and attendance at seminars. In addition, they gain written and oral communication skills through qualifying examinations; presentations in an annual seminar class, at lab meetings, and in journal clubs; attendance at national and international meetings; and preparation of manuscripts for publication. Students obtain teaching experience through a requirement to serve as teaching assistants in undergraduate introductory genetics or evolutionary biology for at least one semester, usually in their second or third year. Students enter graduate school through the recently- expanded Integrated Life Sciences (ILS) umbrella program, which is the primary entry mechanism for students who will enter the Graduate Training Program. During their first semester, students complete three six-week laboratory research rotations where they commit significant effort. This is facilitated by non-teaching fellowships provided by the University of Georgia and a moderate course load during the first semester. Students in the Genetics Graduate Training Program (GTP) are required to first take a gateway course that is designed both to provide broad training in genetics and to build a solid foundation of genetics knowledge and understanding. In addition, they receive formal quantitative training and participate in a student seminar course each semester they are in the GTP. At least two additional formal courses are taken from any combination of the three broad areas of molecular genetics, genomics, and population genetics. The unusual breadth of genetics that students are exposed to throughout their training is a major strength of the program. At the end of their first semester, students choose an advisor with whom they will do their dissertation research. There are currently 42 training faculty across eleven academic units who represent a very wide range of genetic disciplines. To ensure that students complete degree requirements in a timely manner, progress is closely monitored by the Graduate Affairs Committee and by students' dissertation committees. Graduates from this training program over the past 40 years have been highly successful in careers in academia, government, and industry. The training program is dynamic and will continue to produce broadly trained leaders in genetics as it embraces the exciting genetic developments of the 21st Century.