Relative sexual size dimorphism in Centrobolus digrammus (Pocock) compared to 18 congenerics

Abstract

The present research was aimed to study relative sexual size dimorphism of Centrobolus digrammus (Pocock) compared to 18 congenerics. Millipedes illustrate reversed sexual size dimorphism (SSD) as females are larger than males; and corroborate Rensch’s rule as this dimorphism increases with body size. SSD was calculated in 18 species of the genus Centrobolus and illustrated as a regression. The approximate relative position of C. digrammus was shown from measurements taken at Simon’s Town Waterfall, South Africa (March 1997). The size of C. digrammus was 49.9 X 4 mm: 54.5 X 4.8 mm (males: females; n=6) and logged (females/x = 2.993; males/y = 2.790). The mean volume ratio for C. digrammus was 1.599. The evidence suggests the proximate cause for SSD in C. ruber is sexual bimaturism while the ultimate cause in Centrobolus is intersexual competition.