author(s)
Mark Ian Cooper

abstract
Male millipedes may control the duration of copulation and maintain genital contact with females in relation to the intensity of sperm competition. Post-insemination associations were considered in arthropods and the timing of insemination in the millipede Centrobolus inscriptus calculated by artificially-terminated radiolabelled mating. Copula pairs were separated after 1, 2, 3, 4, 5, 10, 20, and 30 minutes of copulation. Ejaculate volumes inseminated did not correlate significantly with the manipulated copulation durations (r = -0.35, df = 8, P = 0.35). High (ca. 2500 dpm) and low values in the first 5 minutes evidenced "instantaneous-insemination" and self-sperm displacement. Instantaneous insemination was demonstrated using artificially terminated mating in Centrobolus inscriptus by showing no relationship between ejaculate volume and copulation duration except for the high and low volumes at the beginning of mating when the male loads and seats the gonopods before adaptive mate-guarding by prolonged copulation.