Aging-related changes in the skulls of Japanese macaques (<i>Macaca fuscata</i>)

Abstract

We investigated aging-related changes in the skulls of Japanese macaques (Macaca fuscata). A total of 145 (70 males, 75 females) skulls from macaques aged 7.0-26.9 years (males) and 7.0-30.7 years (females) were measured for 22 craniometric items. Some skull dimensions increased from young adulthood (7.0 years) to the peak at 13.3-19.0 years in males and at 19.7-22.6 years in females. Some dimensions remained at their peak value right through into very old age whereas others continued increasing during this stage of life. Continued increase of cranial size in adulthood has been also observed in humans, but the magnitude of change was greater in macaques. Facial and mandibular dimensions showed larger and more significant increases than neurocranial dimensions in macaques, as in humans, including facial height, bizygomatic breadth, mandibular body height, and ramus breadth in both sexes. Intertemporal distance and biorbital breadths after 16.0 years of age decreased significantly in males, and cranial and posterior basicranial lengths increased only in males. We suggest that these craniometric changes are associated with the development of the insertion area onto which muscles attach (by accumulation of physical stress). The face and mandible are greatly influenced by tooth loss and/or dental disorders, both of which are evident in humans. In the present study large changes were also found in skulls that had lost several teeth.

Age-Related Changes in the Cranial Thickness of Japanese Macaques ( Macaca fuscata )

“…The peak cranial thickness at many sites in the neurocranium occurred later in females than in males, corresponding to the finding that craniometric age changes were attained later in female than in male macaques (Wang et al;Van Minh et al, 2015). Similarly, the maximal stages of trunk length and epiphyseal unions in the postcranial skeletons of Japanese macaques were reported to occur later in females than in males (Kimura;Hamada, 2008).…”

“…Various factors including environment, genetics, and physiological conditions affect bone dimensions, making it difficult to define age-related changes in bone (Syed & Ng, 2010;Pomchote;Van Minh et al, 2015). In the present study, we controlled the origin of the subjects, rearing conditions (corral cages), and foods (monkey chow and potato supplements) throughout the lifetime of the experimental macaques.…”

“…The aim of the present study was to investigate agerelated changes in the craniofacial thickness of Japanese macaques (Macaca fuscata) of known age and origin, reared in the same condition. Craniometric measurement of agerelated changes have shown that several sizes of the cranium developed in response to muscular force, reproductive cessation, and whole-body aging in macaques (Van Minh et al, 2015). We therefore examined whether age-related changes in cranial thickness are associated with these factors.…”

“…We therefore examined whether age-related changes in cranial thickness are associated with these factors. Because changes in cranial size after dental maturity differ between sexes (Wang et al;Van Minh et al, 2015), we expected to find similar patterns in age-related changes in the cranial thickness of Japanese macaques. Based on the results of the present study, we discussed the implications of age-related changes in human cranial thickness.…”

“…The cranial dimension has been demonstrated to increase after dental maturity in macaques and other nonhuman primates (Jones et al, 2000;Wang et al, 2007;Balolia et al, 2013;Van Minh et al, 2015), as manifested by a slight expansion of the cranial vault. Endocranial volume has also been shown to increase from mid-adulthood to older age in macaques (Van Minh & Hamada, 2017).…”