Size matters in myriapod copulation

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.

Section: Discussionsupporting

confidence: 69%

Section: Discussionmentioning

confidence: 99%

Centrobolus anulatus (Attems, 1934) reversed sexual size dimorphism

Cooper¹

2018

“…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] . Copulations of females were significantly related to the female body width in the presence of sexual size dimorphism in double mating experiments of C. inscriptus [38] . Diplopoda SSD does not negatively regress with body sizes but break Rensch's rule [39] .…”

Section: Discussionmentioning

confidence: 92%

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

Cooper¹

2018

Studies on Centrobolus spp. were reviewed in which mechanisms of selection, sperm competition and cryptic female choice were studied. Approaches (1) quantify size dimorphism and find the selection pressures operating on the sexes, (2) determine the functional significance of male and female genitalia, (3) understand why there should be a conflict of sexual interests in prolonged copulations, and (4) resolve the mechanisms of sperm competition and cryptic female choice in comparing male mating strategies to female sperm usage were included.

“…Diplopoda resemble the majority of invertebrates where SSD is reversed [12] . SSD has consequences for outcomes of sexual encounters in diplopod mating [13][14][15][16][17][18][19] . The allometry of SSD involves the detection of a relationship between body size and SSD and is known by Rensch's rule [20.…”

Section: Introductionmentioning

confidence: 99%

Allometry for sexual dimorphism in millipedes (Diplopoda)

Cooper¹

2018

Self Cite

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.π.r 2 ) and spherical pill millipede size (4/3.π.r 3 ): (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.