Rensch’s rule predict the negative associations between sexual size dimorphism (SSD) and body sizes for relatively larger females. This prediction was tested for forest and savanna diplopods using a geometric morphometric approach using calculations of length and width to derive shape volume based on the mathematical formulae for estimated cylindrical worm-like millipede size (l.p.r2) and spherical pill millipede size (4/3.p.r3): (i) Centrobolus (were collected in February 1996, South Africa) SSD was 0.63-2.89 (1.52±0.35; 267) (ii) Sphaerotherium (extracted from literature) SSD was 1.49-5.36 (2.96±1.40; n=7); (iii) savanna (Calostreptus, Doratogonus, Odontopyge and Spinotarsus were collected in February 1989, Zimbabwe) and forest helminthomorphs (collected in February 1996, South Africa) SSD was 0.88-1.62 (1.26±0.23; 1233). Interspecific variation regressed was SSD (0.63-5.36) on body sizes (n=1273) with no significant negative correlations rejecting Rensch’s rule. Eco-morphological patterns were discussed.
