UC Riverside

The pelvis is the attachment site for vertebrate hindlimbs and is responsible for supporting the weight of the upper body and transferring it to the lower limbs, facilitating balance and mobility. The pelvis is composed of the sacrum, coccyx, and paired hip bones (ilium, ischium, pubis). Research comparing species with different locomotor behaviors indicates that pelvic morphology in terrestrial mammals may be shaped, in part, by evolutionary trade-offs between reproductive demands and locomotor performance. We used the artificially selected High Runner (HR) lines of mice to analyze pelvic morphology in relation to daily movement distance and sex. In this model, outbred house mice (Mus domesticus; Hsd:ICR strain) were bred for increased voluntary wheel-running behavior to create four HR lines and four non-selected Control (C) lines. These lines have been used to study correlated responses in exercise physiology, behavior, neurobiology, and genetics. Whole-body CT images were obtained from 190 mice at generation 93. Pelvic size and shape were analyzed with 3D geometric morphometrics, based on 44 landmarks.We expected divergence in pelvic morphology between the HR and C lines, and that this would be greater for males than for females because the latter are somewhat constrained by reproductive demands. We also tested for differences among the replicate HR lines to examine the possibility of multiple solutions.With body length as a covariate, HR lines did not significantly differ from C lines in pelvic centroid size, but the pelvis was larger in females than males, with no linetype-by-sex interaction. In contrast, pelvic shape (with or without body size or centroid size as a covariate), was affected by both linetype and sex, but with no linetype-by-sex interaction, therefore not supporting our differential constraint hypothesis.At the level of variation among replicate lines, pelvic shape was more dispersed in morphospace in HR lines as compared with C lines, for both sexes. This result suggests "many-to-one mapping" as a mechanism that has led to "multiple solutions" in response to a uniform selective regime imposed on the four replicate HR lines.