Sexual dimorphism in the right pelvic bone of the guinea pig (Cavia porcellus): Geometric morphometric analysis

Abstract

This study tested whether sexual dimorphism in the adult guinea pig right pelvic bone is expressed as differences in centroid size, landmark-based shape, and allometric pattern using computed tomography-derived threedimensional models. A total of 31 adult guinea pigs were initially available, but one female specimen was identified as a marked centroid-size outlier and excluded from inferential analyses; the final analytical sample therefore comprised 11 females and 19 males. Ten fixed landmarks were analyzed on Procrustes-aligned coordinates exported from the landmarking workflow. Centroid size was compared between sexes, raw shape variation was assessed with permutation-based Procrustes ANOVA and principal component analysis, allometry was tested by multivariate regression of shape on log centroid size, and size-corrected shape differences were examined from regression residuals. Males had significantly larger centroid sizes than females (Welch t-test, p = 0.0008). Raw shape differed significantly by sex (F = 14.50, R2 = 0.341, p = 0.0001). The first two principal components explained 40.09% and 15.16% of the total raw shape variance, respectively. Allometry was significant, but the size-by-sex interaction was not (F = 1.61, p = 0.0958), indicating a broadly shared allometric trend in both sexes. After removal of the allometric component, sex-related shape differences remained significant (F = 6.12, R2 = 0.179, p = 0.0001). These findings show that pelvic dimorphism in the guinea pig pelvic bone reflects both size-dependent and size-independent components of variation.