Copulation duration Allometry in Worm-like Millipedes (Diplopoda: Chilognatha: Helminthomorpha)

Abstract

Of many determining factors of copulation duration across arthropods, I reviewed copulation duration variance in mate-guarding worm-like millipedes. The objective wass to calculate copulation duration allometry in worm-like millipedes. The null hypothesis was mean copulation duration and copulation duration variance were independent of body mass. Copulation duration and standard deviation squared for 20 populations of millipedes were obtained from the literature. Copulation duration was strongly correlated with variance (r=0.87, Z score= 5.74, n=21, p<0.01). These ranged from Gigantowales chisholmi (0.09) to Alloporus uncinatus (Mazowe-Hwange) (4238.01) and included some forest species (C. anulatus, C. inscriptus, C. ruber). Copulation duration variance was correlated to female mass (r=0.68, Z score=2.89, n=15, p<0.01). Copulation duration variance was correlated to male mass (r=0.80, Z score=3.85, n=15, p<0.01). There was no significant difference between these correlations (z=-0.67, n=15, 15, p=0.50). Copulation duration was marginally correlated to male mass (r=0.40, Z score=1.55, n=16, p=0.06). Copulation duration was not correlated to female mass (r=0.33, Z score=1.22, n=16, p=0.11). There was no difference between these correlation coefficients (z=0.23, n= 16, 16, p=0.82). Prolonged copulation duration was interpreted to have correlated with the intensity of sperm competition and inversely related to size when intraspecific variance in copulation duration were controlled (equal). Males control the duration of copulation based on mass and intensity of sperm competition.