Sex differences in pelvic size and shape in the striped field mouse from Slovakia

Abstract

Morphometric analysis and evaluation of 260 striped field mice (Apodemus agrarius) were carried out to identify sexual size dimorphism in pelvic bones regarding the age of individuals and the reproductive history of females. Pelvic size was found to differ between subadult and adult individuals of both sexes. A comparison using the Mann-Whitney U test between the right and left parts of the pelvis showed statistically non-significant differences between the pelvis dimensions. In the inter-sexual comparison of both ages (subadult, adult), statistically significant differences were found for only four traits in adults: length of the coxal bone (LP1), width of the ischiopubis (WP1), length of the obturator foramen (LSF) and width of the obturator foramen (WSF). The two indices (WSF/LSF and WP1/LP2) evaluated clearly reflected changes in the pelvic shape, which were most pronounced in adult mice. For the group of subadult males and females, the differences in measured traits and indices were not as pronounced. Several analyses, such as the Mann-Whitney U test, principal component analysis (PCA) as well as discriminant analysis (DFA), showed sex differences in pelvic morphology and shape, although the two sexes overlapped. Similarly, one-way ANCOVA showed that there was a significant difference between the sexes for the adjusted means. Analyses showed that for a given body mass, it appears that females tend to have larger pelvises. Thus, the sexual dimorphism of females was related to pelvic size and shape in A. agrarius. The breeding history showed differences in pelvic dimensions in following direction: the nulliparous < primigravid < primiparous direction.