Sexual dimorphism in the size and shape of the non-obstetric pelvis across anthropoids

New insights into patterns of integration in the femur and pelvis among catarrhines

OBJECTIVES

Integration reflects the level of coordinated variation of the phenotype. The integration of postcranial elements can be studied from a functional perspective, especially with regards to locomotion. This study investigates the link between locomotion, femoral structural properties, and femur-pelvis complex morphology.

MATERIALS AND METHODS

We measured (1) morphological integration between femoral and pelvic morphologies using geometric morphometrics, and (2) covariation between femoral/pelvic morphologies and femoral diaphyseal cross-sectional properties, which we defined as morpho-structural integration. Morphological and morpho-structural integration patterns were measured among humans (n = 19), chimpanzees and bonobos (n = 16), and baboons (n = 14), whose locomotion are distinct.

RESULTS

Baboons show the highest magnitude of morphological integration and the lowest of morpho-structural integration. Chimpanzees and bonobos show intermediate magnitude of morphological and morpho-structural integration. Yet, body size seems to have a considerable influence on both integration patterns, limiting the interpretations. Finally, humans present the lowest morphological integration and the highest morpho-structural integration between femoral morphology and structural properties but not between pelvic morphology and femur.

DISCUSSION

Morphological and morpho-structural integration depict distinct strategies among the samples. A strong morphological integration among baboon's femur-pelvis module might highlight evidence for long-term adaptation to quadrupedalism. In humans, it is likely that distinct selective pressures associated with the respective function of the pelvis and the femur tend to decrease morphological integration. Conversely, high mechanical loading on the hindlimbs during bipedal locomotion might result in specific combination of structural and morphological features within the femur.

Pelvic shape change in adult Japanese macaques and implications for childbirth at old age

Pelvic morphology exhibits a particular sexual dimorphism in humans, which reflects obstetrical constraints due to the tight fit between neonates and mothers. Huseynov et al. [Proc. Natl. Acad. Sci. U.S.A. 113, 5227-5232 (2016)] showed that in humans, pelvic sexual dimorphism is greatest around the age of highest fertility, and it becomes less marked in association with menopause in females. They proposed that this reflects changes of obstetrical versus locomotor functional demands in females. It remains unknown whether such developmental adjustment of the pelvic morphology is unique to humans. Macaques exhibit human-like cephalopelvic proportions, but they lack menopause and usually maintain fertility throughout adulthood. Here, we track pelvic development in Japanese macaques from neonate to advanced ages using computed tomography-based data. We show that female pelvic morphology changes throughout adult life, reaching the obstetrically most favorable shape at advanced ages rather than around primiparity. We hypothesize that pelvic morphology in Japanese macaques is developmentally adjusted to childbirth at advanced ages, where obstetrical risks are potentially higher than at younger ages. Our data contribute to the growing evidence that the female primate pelvis changes its morphology during the whole lifespan, possibly adjusting for changing functional demands during adulthood.

Morphometric analysis of the size-adjusted linear dimensions of the skull landmarks revealed craniofacial dysmorphology in Mid1-cKO mice

BACKGROUND

The early craniofacial development is a highly coordinated process involving neural crest cell migration, proliferation, epithelial apoptosis, and epithelial-mesenchymal transition (EMT). Both genetic defects and environmental factors can affect these processes and result in orofacial clefts. Mutations in MID1 gene cause X-linked Opitz Syndrome (OS), which is a congenital malformation characterized by craniofacial defects including cleft lip/palate (CLP). Previous studies demonstrated impaired neurological structure and function in Mid1 knockout mice, while no CLP was observed. However, given the highly variable severities of the facial manifestations observed in OS patients within the same family carrying identical genetic defects, subtle craniofacial malformations in Mid1 knockout mice could be overlooked in these studies. Therefore, we propose that a detailed morphometric analysis should be necessary to reveal mild craniofacial dysmorphologies that reflect the similar developmental defects seen in OS patients.

RESULTS

In this research, morphometric study of the P0 male Mid1-cKO mice were performed using Procrustes superimposition as well as EMDA analysis of the size-adjusted three-dimensional coordinates of 105 skull landmarks, which were collected on the bone surface reconstructed using microcomputed tomographic images. Our results revealed the craniofacial deformation such as the increased dimension of the frontal and nasal bone in Mid1-cKO mice, in line with the most prominent facial features such as hypertelorism, prominent forehead, broad and/or high nasal bridge seen in OS patients.

CONCLUSION

 While been extensively used in evolutionary biology and anthropology in the last decades, geometric morphometric analysis was much less used in developmental biology. Given the high interspecies variances in facial anatomy, the work presented in this research suggested the advantages of morphometric analysis in characterizing animal models of craniofacial developmental defects to reveal phenotypic variations and the underlining pathogenesis.