Centrobolus sagatinus sexual size dimorphism based on differences in horizontal tergite widths

Abstract

The forest genus Centrobolus of millipedes belonging to the Order Spirobolida is distributed along the eastern coast of southern Africa. Sexual size dimorphism (SSD) can be explained by mate-guarding in the form of prolonged copulation and fecundity selection. Width and length were analysed in Centrobolus to derive SSD in 21 species. The size of C. sagatinus collected in South Africa was calculated as 48, 33333 X 6,64444mm (n=9) according to the formula for a cylinder. Males measured 48,5 ± 1,732051 X 6,225 ± 0,170783 mm (μ ± σ; n=4) and females 48,2 ± 4,636809 X 6,98 ± 0,248998 mm (μ ± σ; n=5). An analysis from data presently available showed average SSD for C. sagatinus was 1,009222, differing from 1 (t=-2, 645751; p=0,033146; p≤0, 05; n=4). C. sagatinus dimorphism was based on a 0, 75 ± 0, 25 mm difference in horizontal tergite width (t=-1.91326; p=0.036891; n=9). This sexual dimorphism resembles C. inscriptus female width which is positively related to copulation duration and larger females are more fecund.