Is a prominent sternite related to spine length, spine number, copulation duration, and male width in Centrobolus Cook, 1897?

Abstract

Four species of Centrobolus were identified (C. fulgidus, C. anulatus, C. inscriptus, C. ruber) based on morphology and confirmed using Scanning Electron Microscopy (SEM) of Gonopod structure. Two sets of linear measurements were made from the SEM micrographs: (1) prominence of the stemite, and (2) length of the spines present on the distal knob (which were counted). Copulation duration and male width were recorded. Sternite prominence and spine length were positively related (Kendall's τ=1, Z score=2.32, n=3, p=0.01). Sternite prominence and spine number were inversely related (Kendall's τ=-1, Z score=-2.32, n=3, p=0.01). Spine length and spine number were inversely correlated (Kendall's τ=-1, Z score=-2.32, n=3, p=0.01). There was a significant correlation between sternite prominence and copulation duration in the four species (Pearson's r=0.97, Z score=2.14, n=4, p=0.02). Sternite prominence was positively related to male width (r=0.96, Z score=1.90, n=4, p=0.03). This supports the function of the sternite as (hypoallometric) devices adapted toward sperm competition.