Growth of functional cranial components in Saimiri sciureus boliviensis (Cebidae): a longitudinal study

Ten male Saimiri sciureus boliviensis (Cebidae) born at the Centro Argentino de Primates (CAPRIM) were divided into a control group (five animals fed ad libitum on a 20% protein diet) and an undernourished group (five animals fed ad libitum on a 5% protein diet) at weaning (seven months old). Each animal was radiographed monthly from both later-lateral and dorsal-ventral views, from the first to the third year of age. The length, width and height of the optic, respiratory, and masticatory components of the face and anterior neural, middle neural, and posterior neural components were measured in the radiographs. Volumetric (VI) and morphometric (MI) indices were calculated for each component. Correlations and simple linear regressions with respect to age were performed. In the face, two components -respiratory and masticatory- showed the greatest growth rate. In the neurocranium, the middle neural component grew most, approaching the rate observed for the component of the lowest growth in the face (optic). The anterior neural and posterior neural components showed the lowest -although significant- growth rates of the skull. The determination coefficients showed that linearity explained from 12% (posterior neural component) to 74% (masticatory component) of the variation, the remainder being attributed to shape changes and noise effects. The neurofacial rate showed a high level (80%) of nonlinearity since the neurocranium grew almost 1/3 with respect to the face. The morphometric indices showed that only the masticatory component was linear to the face. While the respiratory component grew more, the optic one grew less than the whole face. Only the anterior neural component kept linearity with the neurocranium. While the middle neural component grew more, the posterior neural one grew less than the whole neurocranium. Significant alterations due to undernutrition were seen in both major components. While the three facial and the anterior neural components showed correlation coefficients lower -but significant- than in controls, in the remaining indices -morphometrics included- the correlation values were abruptly broken. The slopes of the regressions which remained significant showed that undernutrition affected mainly the components with greater growth rates (respiratory, masticatory, and middle neural). Secondarily affected were those with lower growth rates (optic, anterior neural and posterior neural), despite their function and according to the histology of the organs they support and protect.