Sperm mobility: Phenotype in roosters (Gallus domesticus) determined by concentration of motile sperm and straight line velocity

Previous research demonstrated that sperm mobility, i.e., the net movement of a sperm population, is a quantitative trait of the domestic fowl. Howeve r, the cellular basis for this trait was un-known. In the present work, ind ividual motile sperm were evaluated with a Hobson SpermTracker in order to identify one or more properties of motile sperm that could account for vari ation in sperm mobility observed among males. A method was validated for as sessing sperm motion over an erythrocyte monolayer at body temperature. A s mall-scale experiment with roosters from the tails and center of a normal d istribution of sperm mobility phenotypes (n = 33 roosters) demonstrated tha t straight line velocity (VSL) and motile concentration were critical to ex pression of phenotype. The importance of these variables was confirmed with a large-scale experiment using a representative subpopulation (n = 100 roo sters). VSL of individual sperm at 41 degrees C ranged between 5 and 100 mu m/sec. VSL averaged 32, 39, and 40 pml sec for low, average, and high sper m mobility phenotypes. Sperm were diluted to 1.2 x 10(6)/ml for motion anal ysis. Mean motile concentrations were 0.52, 0.84, and 0.95 x 10(6)/ml for l ow average, and high sperm mobility phenotypes. Motile concentration was co rrelated with sperm mobility (r = 0.71). VSL appeared to have an additive e ffect as it was correlated with straightness of sperm cell trajectory (r = 0.79).