Fire millipedes obey the female sooner norm in cross mating Centrobolus (Myriapoda)

Abstract

Sexual mediation of copulation duration is reviewed in arthropods. Copulation duration and ejaculate volume were recorded in cross mating Centrobolus to test species' mediation differences. Conspecific C. inscriptus copulation durations were long (170.0 ± 49.3 min, n = 46), C. annulatus copulation durations were short (39.4 ± 18.6 min, n = 8), while mating between heterospecifics (C. inscriptus X C. annulatus) had the shortest copulation durations (12.4 ± 10.6 min, n = 6); when re-mating interval, sexual size dimorphism, sex ratio and ejaculate volume were controlled. ⺠(the female sooner norm) suggests sizeassortative mating without a size based preference in these mate-guarding millipedes.

Allometry for sexual dimorphism in millipedes (Diplopoda)

“…In the millipede Doratogonus uncinatus female choice for mating partners is "size selective" [78] . The cross-mating experiments in Centrobolus suggest a combination of size assortative mating without a size based preference operates [79] . Further studies of diplopod sexual dimorphism may include more taxa and make use of the length and width measurements to calculate volumes using the geometric morphometric approach shown here for finding causal relationships of dimorphism.…”

Centrobolus dubius (Schubart, 1966) Monomorphism

“…C. dubius (Schubart) were collected at Fransches Kraal near Gans Bay, South Africa. Millipede SSD was also calculated in the genus Centrobolus [5][6][7][8][9][18][19]. A regression of male volume on female volume was used to show the position of 18 species and the size of C. dubius was taken as volumetric measurement and inserted into a Microsoft (MS) Excel spreadsheet and converted using the log (mathematical) equation.…”

“…Millipedes illustrate reversed sexual size dimorphism (SSD) and females are larger than males [1][2][3][4] . Diplopoda are underrepresented in allometric analyses of sexual size dimorphism (SSD), although sexual size differences are known in body mass, length, width and leg dimensions of over half the taxa studied [1][2][5][6][7][8][9][10] . Size differences correlate with factors such as color, sexes, species, urbanisation and water relations [4,[10][11][12] .…”

Sperm dumping in Centrobolus inscriptus Attems (Spirobolida: Trigoniulidae)

“…The active release of ejaculate post-insemination and copulation duration was studied in Centrobolus inscriptus where sperm or ejaculate precedence correlates with prolonged second copulation duration and re-analysis of sperm volumes from single and double mating experiments with 24 hour (h) delays post-mating [14][15][16][17][18][19][20][21][22][23][24][25][26] . In order to provide supporting evidence for female control of ejaculate and sperm dumping after mating, ejaculate volumes released from females 24h after mating was studied and compared alongside double matings.…”