When is the change in sperm precedence in the millipede <em>Centrobolus inscriptus</em> (Attems, 1928) (Diplopoda, Pachybolidae)?

Abstract

There were three scenarios of sperm precedence; first-male, last-male and no order effect. I replicated the H3+ radiolabel technique and showed sperm precedence patterns in the sexually dimorphic millipede Centrobolus inscriptus (Attems, 1928). Disintegration rates (D.P.M.) from single labelled mating were significantly lower than those of unlabelled-labelled mating (U=-2.6, n=13, p=0.005) but not to labelled-unlabelled double mating (U=0.45, n=14, p=0.65). In the initial experiment without the interval V2=43.66% and with the interval V2=74.59%. D.P.M. from the immediate dissections of twice mated females were higher (Z = 3.81, n = 12, 12, P = 0.0001) than females with a remating interval of up to 24 hours. When the experiment was replicated significant differences (H = 30.67, d.f. = 5, P = 0.00001) between total D.P.M values were again found. D.P.M. values were higher when second mating followed immediately after the first (V2= 21%). D.P.M. from labelled-unlabelled mating were significantly lower than the D.P.M. of unlabelled-labelled mating after 10 hours (600 minutes) resulting in a reduction of up to 57% in favour of the second male when second-male ejaculate volume precedence arises to 77%.