Relative sexual size dimorphism in Centrobolus fulgidus (Lawrence) compared to 18 congenerics

Abstract

The present research was aimed to study relative sexual size dimorphism of Centrobolus fulgidus (Lawrence) 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. fulgidus was shown from measurements taken at Richards Bay Minerals (February 1996) and St. Lucia Estuary (December 1996) in South Africa. The size of C. fulgidus was 56.2 X 5.4 mm: 63.5 X 5.2 mm (males: females; n=11) and logged (x = 3.398; y = 3.301). The mean volume ratio for C. fulgidus was 1.2505. The evidence suggests the proximate cause for SSD in C. ruber is sexual bimaturism while the ultimate cause in Centrobolus is intersexual competition.

Centrobolus dubius (Schubart, 1966) Monomorphism

“…Previous studies on SSD in invertebrates and these results consistently give a positive correlation and break the rule [5,[21][22][23][24][25]26] . Figure 1 shows the finding for Centrobolus dubius where the regression of log male volume on log female volume was highly significant with a positive slope of 1.…”

A review of studies on the fire millipede genus centrobolus (diplopoda: trigoniulidae)

“…C. fulgidus was similar to C. inscriptus with small males and larger females compared to 18 Centrobolus species for which data was available [35] . C. ruber males and females followed the trend for SSD and (break) Rensch's rule in Centrobolus [36] . Copulation duration related to male length in double mating C. inscriptus and second mating intra-pair SSD was under female control and affected ejaculate precedence [37] .…”

Allometry for sexual dimorphism in millipedes (Diplopoda)

“…However, mass and volume do not provide equal measures of SSD. In the case where both mass and volume were measured (C. fulgidus) this was evident [46] . In order to obtain more accurate results, the analysis for (1) and (2) included only volume (Fig.…”