Sex-Related Shape Variation and Right-Left Asymmetry in the Stylopodium and Zeugopodium of Guinea Pigs

Abstract

The aim of this study was to identify the presence and magnitude of right-left asymmetry in the fore- and hindlimb long bones of adult guinea pigs (Cavia porcellus), and, in parallel, to evaluate sex-related differences in shape and size in the same bones. For this purpose, the stylopodium and zeugopodium bones were analyzed together. Computed tomography data were obtained from all animals under a standard protocol, three-dimensional bone models were generated from these datasets, and these models formed the basis for the geometric morphometric analyses. The analyses showed that sex accounted for a small but consistent proportion of shape variation (approximately 5-7%) in the antebrachium, femur and crus, whereas this effect was more limited in the humerus. Asymmetry analysis based on paired right-left data revealed that directional asymmetry was generally low, whereas fluctuating asymmetry varied across bones. The highest asymmetry was detected in the antebrachium, the crus showed an intermediate level, and the stylopodial elements, humerus and femur, were comparatively more symmetrical. This pattern is consistent with the biomechanical expectation that small right-left deviations tend to accumulate in distal and functionally more active forelimb segments that are positioned farther from the trunk. In conclusion, the findings indicate that asymmetry arises gradually as a function of bone position and functional use rather than from a single growth error, and that distal forelimb elements should therefore be given particular attention in asymmetry studies.