Centrobolus anulatus (Attems, 1934) reversed sexual size dimorphism

Abstract

The present research aimed to study relative sexual size dimorphism of Centrobolus anulatus compared to congenerics. Millipedes illustrated reversed sexual size dimorphism (SSD) as females were larger than males and broke the rule as this dimorphism increased with body size. SSD was calculated in 18 species of the genus Centrobolus and illustrated as a regression. The approximate relative position of C. anulatus was shown from measurements taken in South Africa (2018). The average size of C. anulatus was 74.23529412 X 5.685882 mm (n=17); males measured 69.2 X 5.264 mm (n = 5) and females were 76.3 X 5.861667 mm (n = 12). Log volume measurements were (females/x = 3.31359939 mm 3 ; males/y = 3.2377543 mm 3 ). The difference between the correlation coefficients for the species and the genus were not highly significant (ra = 0.86207, rb = 0.85; na = 17, nb = 18; Z = 0.12; P (one-tailed) = 0.4522, P (twotailed) = 0.9045). The mean volume ratio for C. anulatus was 1.02342521 which differed from 1 (t=3.59722; p-value = 000747; p <.01; n=17). Evidence suggests sexual bimaturism as proximate cause and competition as ultimate cause for SSD in Centrobolus.

Centrobolus silvanus dimorphism based on tergite width

“…silvanus shows sexual size dimorphism with small males and larger females based on the fi nding of differences in horizontal tergite width. Sexual dimorphism resembles C. inscriptus and C. sagatinus female width which is positively related to copulation duration and larger females are fecundity selected [18,21].…”

“…Centrobolus species based on tergite width are clearly recognisable [16,18]. Because SSD was signifi cantly different Sexual dimorphism resembles C. inscriptus female width which is positively related to copulation duration and larger females are probably more fecund [21].…”

“…C. silvanus (Attems) were collected from Kentani District and Knysna, South Africa. SSD was calculated based on the volumes for 22 species in the genus Centrobolus [16,18] and included data for C. richardi.…”

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“…The red millipede genus Centrobolus is well known for studies on sexual size dimorphism (SSD) and displays prolonged copulation durations for pairs of individuals of the species [3][4][5][6][7][8] . Centrobolus is distributed in temperate southern Africa with northern limits on the east coast of southern Africa at -17° latitude South (S) and southern limits at -35° latitude S. It consists of taxonomically important species with 12 species considered threatened and includes nine vulnerable and three endangered species [19] .…”

“…The genital morphology and mechanics of copulation were figured in four Centrobolus species [1] . These are worm-like millipedes that have female-biased SSD [3][4][5][6][7][8][11][12][13] . From the results correlations between coleopod sternite prominence, spine length, and spine number were checked.…”