An interdisciplinary systems approach to study sperm physiology and evolution.

Optical trapping is a noninvasive biophotonic tool that has been developed to study the physiological and biomechanical properties of cells. The custom-designed optical system is built to direct near-infrared laser light into an inverted microscope to create a single-point three-dimensional gradient laser trap at the microscope focal point. A real-time automated tracking and trapping system (RATTS) is described that provides a remote user-friendly robotic interface. The combination of laser tweezers, fluorescent imaging, and RATTS can measure sperm swimming speed and swimming force simultaneously with mitochondrial membrane potential (MMP). The roles of two sources of adenosine triphosphate in sperm motility/energetics are studied: oxidative phosphorylation, which occurs in the mitochondria located in the sperm midpiece, and glycolysis, which occurs along the length of the sperm tail (flagellum). The effects of glucose, oxidative phosphorylation inhibitors, and glycolytic inhibitors on human sperm motility are studied. This combination of photonic physical and engineering tools has been used to examine the evolutionary effect of sperm competition in primates. The results demonstrate a correlation between mating type and sperm motility: sperm from polygamous (multi-partner) primate species swim faster and with greater force than sperm from polygynous (single partner) primate species. In summary, engineering and biological systems are combined to provide a powerful interdisciplinary approach to study the complex biological systems that drive the sperm toward the egg.