Sperm storage and duration of fertility in female ostriches (Struthio camelus)
In two experiments, one carried in South Africa and the other in Western Australia, the duration of sperm storage and the fertile period following separation of sexes were investigated by egg break-out and by counting the sperm in the perivitelline membrane (spermOPVL) above the germinal disc (GD) region. Fertilisation status was determined by the appearance of the GD. The perivitelline membrane above the GD was collected to count sperm under fluorescence following staining with 4′,6′-diamidino-2-phenyindole (DAPI). In both experiments, after the males were removed, the rate of lay declined by about 50% within a week. Following separation, spermOPVL were detected for up to four weeks and fertilised eggs were laid for nearly the same duration. The loss of sperm followed an approximately logarithmic function and sperm numbers declined at rates similar to that of the turkey. Since the duration of sperm storage was longer than indicated by clutch duration, ostrich clutch size might be larger than reported or female ostriches might store sperm for up to two clutches. Fertilisation rate in ostrich eggs is high because most eggs contain excessive numbers of sperm and very low numbers of sperm appear sufficient to achieve fertilisation.