This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).
The International Research Fellowship Program enables U.S. scientists and engineers to conduct nine to twenty-four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad.
This award will support a twenty-four-month research fellowship by Dr. Leanna M. Birge to work with Dr. Andrew Pomiankowski at University College London in the United Kingdom and with Dr. Gerald Wilkinson at the University of Maryland in the U.S.
Female multiple mating creates an arena for competition to occur among ejaculates. In response, males employ a variety of mechanisms to bias their fertilization success, such as incapacitation. However, the importance of incapacitation as a mechanism for sperm precedence is controversial because it is unclear how a male can damage a rival?s ejaculate without also damaging his own. To evaluate the utility of incapacitation and identify its agents, a system is needed in which genetic differences between competitors? ejaculates can be identified. Stalk-eyed flies provide such a system. In Cyrtodiopsis whitei, sperm from males that produce unbiased sex ratios incapacitate sperm from males that produce female-biased sex ratios caused by X chromosome meiotic drive. In this project, we conduct two complementary studies using this system: a test of the robust nature of incapacitation and a molecular characterization of proteins associated with incapacitation. To assess the strength of incapacitation, adult diet is manipulated using a population and protocols developed at University College London and drive and non-drive males are competed in an in vitro sperm viability assay developed at University of Maryland. Analysis of variance is performed across treatments on live/dead sperm counts. A priori, drive males are expected to overcome incapacitation in the low protein diet treatment due to changes in protein composition caused by dietary stress to non-drive males. The molecular portion of the project is conducted at the University of Maryland and focuses on identifying changes in ejaculatory protein profiles associated with incapacitation. A portion of this work includes the construction of expressed sequence tag (EST) libraries from testes and male accessory glands. Tandem mass spectroscopy is performed on three different combinations of seminal vesicle/accessory gland samples as well as an internal standard to identify protein profiles. Tandem mass spectroscopy results are compared to EST libraries and differences between treatments in protein composition and expression are quantified to identify candidate incapacitation genes.
Broader impacts of the proposed work include advanced training for the postdoctoral fellow and University of Maryland undergraduate students. In addition, the project fosters international collaboration between the postdoctoral fellow and two senior investigators in the UK and US. Results from this study have the potential to provide insight into sperm development and dysfunction, which have biomedical relevance for understanding causes of male infertility. Finally, a large amount of DNA sequence information is deposited in online repositories, thereby enhancing the ability of other investigators to conduct comparative genomic studies.
