How Multivariate Ejaculate Traits Determine Competitive Fertilization Success in Drosophila melanogaster

• DOI: 10.1016/j.cub.2012.06.059
• Publication Date: 2012-07-26T15:18:19Z
• Authors: Stefan Lüpold; Mollie K. Manier; Kirstin S. Berben; Kyle J. Smith; Bryan D. Daley; Shannon H. Buckley; John M. Belote; Scott Pitnick
• Keywords: Male; 0301 basic medicine; Genetically Modified; 1100 General Agricultural and Biological Sciences; Animals, Genetically Modified; 10127 Institute of Evolutionary Biology and Environmental Studies; Ovum Interactions; 03 medical and health sciences; 1300 General Biochemistry, Genetics and Molecular Biology; Drosophila melanogaster: physiology; Drosophila melanogaster: genetics; Animals; Fertilization: genetics; Sperm-Ovum Interactions; Agricultural and Biological Sciences(all); Sperm Count; Biochemistry, Genetics and Molecular Biology(all); Genetic Variation; Spermatozoa; Sperm; Drosophila melanogaster; Fertilization; Spermatozoa: physiology; Sperm Motility; 570 Life sciences; biology; 590 Animals (Zoology); Female; Sperm Capacitation

Success in sperm competition, occurring whenever females mate with multiple males, is predicted to be influenced by variation in ejaculate quality and interactions among competing sperm. Yet, apart from sperm number, relevant ejaculate characteristics and sperm-sperm interactions are poorly understood, particularly within a multivariate framework and the natural selective environment of the female reproductive tract. Here, we used isogenic lines of Drosophila melanogaster with distinguishable sperm to demonstrate and partition genetic variation in multiple sperm quality and performance traits. Next, by competing males from different lines, we show how rival sperm significantly influence each other's velocity and reveal that males with relatively slow and/or long sperm better displace rival sperm and resist displacement, thus avoiding ejection by the female from her reproductive tract. Finally, we establish fitness consequences of genetic variation in sperm quality and its role in securing a numerical advantage in storage by showing that offspring paternity is determined strictly by the representation of stored, competing sperm. These results provide novel insight into complex postcopulatory processes, illustrate that different ejaculate traits are critical at different biologically relevant time-points, and provide a critical foundation for elucidating the role of postcopulatory sexual selection in trait diversification and speciation.