An ontogenetic approach to facial variation in three Native American populations.

Various explanations have been formulated regarding high levels of craniofacial variation among Native American populations but the contribution of developmental processes to the establishment of these patterns of variation remains unknown. In this study, we compare facial morphology in ontogenetic series of three Native South American populations, one hunter-gatherer group and two farmer groups, in order to test the null hypothesis that indicates that the pattern of facial differentiation between populations does not change during ontogeny. If diet-related factors contribute to outline facial morphology, it is likely to find greater differences between hunter-gatherer and both farmer groups than between two groups of farmers and this differentiation is expected to increase with age, especially in those structures that are influenced by the mechanical load of mastication. According to our results, hunter-gatherers clearly differ from the two groups of farmers. Non-heritable factors linked to diet, such as nutritional content of food, may increase differentiation across ontogeny in some cases. However, as hunter-gatherers were clearly separated from farmer populations during entire postnatal ontogeny, an important proportion of size variation may not necessarily reflect eco-sensitive changes. Consequently, the hypothesis cannot be completely rejected.

Craniometric variation and the settlement of the Americas: testing hypotheses by means of R-matrix and matrix correlation analyses.

New archaeological findings and the incorporation of new South American skull samples have raised fundamental questions for the classical theories of the Americas' settlement. The aim of this study was to estimate craniometric variability among several Asian and Native American populations in order to test goodness of fit of the data to different models of ancient population entries and dispersions into the New World. Our data set includes Howells' variables recorded on East Asian, North American, and South American natives (except for Na-Dene speakers). Five Fuego-Patagonian samples and one Paleoamerican sample were also included. A multivariate extension of the R-matrix method for quantitative traits was used to obtain Fst values, which were considered estimations of intergroup variation. Three main models for the peopling of the New World were represented in hypothetical design matrices. Matrix permutation tests were performed to quantify the fit of the observed data with 1) geographical separation of the samples and 2) three ways of settlement, which were the Three Migration Model (TMM), the Single Wave Migration model (SWM), and the Two Components Settlement Model (TCS). R-matrix results showed high levels of heterogeneity among Native Americans. Matrix permutation analyses suggested that the model involving high Amerindian heterogeneity and two different morphological patterns or components (derived "Mongoloid" vs. generalized "non-Mongoloid") explains better the variation observed, even when the effects of geographical separation are removed. Whether these patterns arose as a result of two separate migration events or by local evolution from Paleoamericans to Amerindians remains unresolved.

Effect of undernutrition on cranial components and somatotroph-lactotroph pituitary populations in the squirrel monkey (Saimiri sciureus boliviensis).

The aim of the present study was to investigate in monkeys the effects of undernutrition on neurocranial and facial components, correlated with a histometric and ultrastructural analysis of somatotroph (growth hormone, GH) and lactotroph (prolactin, PRL) pituitary populations. Twenty Saimiri sciureus boliviensis (Cebidae) of both sexes were employed. The monkeys were born in captivity and when they reached 1 year of age, they were separated into two groups: control and undernourished animals. They were fed ad libitum a 20% and 10% protein diet, respectively. The monkeys were radiographed when they were 3 years old in order to measure the length, width and height of the anterior, middle and posterior components of the neurocranium, as well as those of the masticatory, respiratory and optic components of the face. The volumetric and morphometric indices were then calculated. After the sacrifice, pituitary glands were processed for light and electron microscopy. The quantitative immunohistochemistry revealed a decrease in the volume density and cell density of both GH and PRL cells from malnourished animals when compared to control ones. The ultrastructural study showed changes suggestive of cellular hyperfunction for both types of cells in the former experimental group. Under nutrition also affected the size of the cranial components, with males being more affected than females; brain weight was, however, nonmodified by stress, with the brain/body ratio difference being the same for both sexes. We conclude that in monkeys, experimental undernutrition produces a decrease in the pituitary GH and PRL cell populations, in some way related to changes in the cranio-facial morphometric patterns.

Growth of skeletal components in the young squirrel monkey (Saimiri sciureus boliviensis): a longitudinal experiment.

A functional skeletal criterion, as an extension of the van der Klaauw's cranial theory, was adopted in the present study. The null hypothesis tested was: "The major skeletal components of the platyrrhine body grow linearly, regardless of their functional dependence to different demands." The acceptance of the hypothesis will imply that all Saimiri skeletal growth may be satisfactorily explained by independent variables in a single equation. The rejection will suggest that such skeletal growth patterns have to be explained by variables in several different equations, and perhaps these equations may vary with the effect of sex and undernutrition. Control and undernourished squirrel monkeys were radiographed monthly for 2 years; they were also measured; and their volumetric and morphometric neurocranial, facial, and pelvic indices were calculated. The curves that best described each of the 24-point sequences were obtained. Three main growth patterns were observed: 1) Simple linear (femur length for all groups, and pelvic index for control and undernourished females), for which the simple regression equation explained more than 95% of the variation; 2) Complex linear (pelvic index for control and undernourished males, and neurocranial and facial indices for all of the groups), for which more than 95% of the variation was explained by one of the four four-function type equations; and 3) Noncorrelated with age (neurofacial index for undernourished males, and pelviofemoral index for control females and undernourished males and females), which showed nonsignificant correlations with respect to age. The food intake and the oscillations of the environmental temperature might help to explain the undulating growth trajectory observed in the complex linear components.

Body growth and food intake in moderately and severely malnourished rats.

A longitudinal study with eighty-six rats (Rattus norvegicus albinus var. Wistar) of both sexes was made. The aim was to express adaptability to malnutrition in terms of Age-of-Fitness Point (AFP) and Trend-to-Fitness Stage (TFS). The AFP means the age in which both control and malnourished animals show the same Relative Food Intake (RFI) value, expressed in mg of food intake per g of body weight. The TFS means the percent of RFI reached by the malnourished animals at a given age stage. A TFS=70 for example, means that the animals have to gain 30% of RFI to reach its AFP. Growing animals were submitted to one of the following treatments: control (fed on a stock diet ad libitum), moderate malnutrition (fed on 1/2 of the daily stock diet of a control of the same age and sex) and severe malnutrition (fed on 1/3 of the mentioned diet). Body weight and food intake of all of the animals were registered every ten days, when they were from 20 to 80 days old. Relative Food Intake (RFI) was calculated dividing the food intake (mg) of each animal/day by its respective body weight (g). The RFI data series belonging to each sex and treatment was obtained. The significance of the three independent variables (age, sex, and nutrition) was tested by multiple regressions. Covariation and degree of linearity between RFI and age were tested by simple correlation and simple regression tests. The intercepts of the regressions were all significant. For both sexes they were greater in controls than in the moderately malnourished group, in the latter being greater than in the severely malnourished group. The slopes were significant and negative in all of the groups. While, in males and females, control and moderately malnourished rats showed little differences, the severely malnourished slopes were, respectively, 3.2 and 2.4 times lower than in controls. In controls there were sexual differences for RFI correlated with age which were not present in the malnourished groups. The AFP was calculated by extrapolation: 80-90 days of age in males, with RFI of 80 mg/g, and 100-110 days of age in females, with RFI of 70 mg/g. In males TFS was 29.5% and 88.6 % in moderate and severe malnutrition, respectively. In females these values were 9.1% and 63.2%, respectively. Sexual dimorphism in TFS was significant in the moderately malnourished animals and nonsignificant in the severely malnourished ones.

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.

[Effect of gonadal hormones on sexual dimorphism in malnutrition substrates]. / Efecto de las hormonas gonadales sobre el dimorfismo sexual en substrato de desnutrición.

The environmental effect on growth and sexual dimorphism is mediated by endocrinological dysfunctions. It was shown that malnutrition acts on the hypotalamus-pituitary-glandular axis. An experiment was made in Wistar rats to determine the effect of some gonadic hormones on the functional components of the skull to which sex dimorphism was alterated by a postnatal undernutrition. The effects of these hormones in restoring sexual cranial dimorphism was tested. Four treatments were applied: control, with food intake ad-libitum; undernutrition (50% of the control food intake); undernutrition plus periodic injections of testosterone and estradiol to males and females, respectively and sham-operated animals, which were injected with oil vehicle only. A radiological longitudinal study was performed between 20 and 80 days of postnatal age. The length width and height of the neural and facial components were measured on each radiograph. Data were processed by ANOVA and Mann-Whitney statistical tests were performed by means of the SYSTAT 7.0 statistical package. Results showed that gonadic hormones restored the sexual cranial dimorphism by stimulating (testosterone) or suppressing (estradiol) the growth of the cranial components.

Influence of intrauterine blood supply on cranial growth and sexual dimorphism at birth.

Many experimental studies of the effects of placental blood flow on growth exist. Nevertheless, few of them deal with the relationship between impaired uterine blood supply, and cranial growth and sex differentiation. The object of the present study was to investigate the impact of intrauterine growth retardation (IUGR) on sexual cranial dimorphism in the newborn rat. Three experimental groups were employed: (a) control; (b) operated (IUGR), in which both uterine vessels were partially bent in the 15th day of gestation; and (c) sham-operated, identical to (b) but without vessel bending. At birth, pups were weighed, and their bodies and craniums, measured. In the cases of asymmetric distributions, data were logarithmically transformed. A multi-way analysis of variance (ANOVA) and LSD post-hoc tests were used to find out differences between experimental groups and sex. Controls had significant sex differences in body and cranial variables. The prenatal growth of IUGR pups was significantly inhibited. Body and facial variables were more affected than the neurocranial ones. Undernutrition produced body and cranial size changes. Since IUGR affected male more than female growth, sex dimorphism was clearly reduced in all variables which were dimorphic in controls.

Cranial growth in Saimiri sciureus (Cebidae) and its alteration by nutritional factors: a longitudinal study.

Ten male Saimiri sciureus boliviensis (Cebidae), born at the Centro Argentino de Primates (CAPRIM), were grown in captivity. At weaning (6 months old), five individuals were fed ad libitum on a 20% protein diet (controls). The other five animals were fed ad libitum on a 5% protein diet (malnourished). Animals were radiographed monthly. The length, width, and height of the anterior, middle, and posterior components of the neurocranium, and those of the masticatory, respiratory, and optic components of the face were measured. A pattern of high growth rate was observed in both the three facial and the middle neural components. The anterior and posterior neural components showed a pattern of low rate of growth. The growth behavior of each variable was also different. Lengths grew more than widths and heights in the facial components, whereas widths grew more than heights and lengths in the neurocranium. Malnutrition delayed growth in size and altered the normal shape changes. High-patterned variables, such as masticatory and respiratory lengths, and the anterior and middle neural widths were particularly affected. The masticatory and the middle neural components underwent the greatest growth arrest. The optic and the respiratory components suffered a mild effect. The anterior and the posterior neural components were affected to a lesser degree.

Orthocephalization in the postweaning squirrel monkey.

Twenty male squirrel monkeys (Saimiri sciureus boliviensis) raised in captivity were allotted to one of the following groups: weanling control (C6) sampled at 6 months of age; young control (C24) fed ad libitum on a control diet and killed at 24 months of age; and malnourished (M24) fed ad libitum on a low-protein diet and sampled at 24 months of age. Cranial points and the lateral semicircular canals were marked. On each skull, a strict lateral teleradiograph was taken, and the lengths of the midsagittal chords and their angles with respect to the vestibular line were measured. Age changed the lengths in about 70% of the chords and more than 50% of the angles. Malnutrition arrested about 50% of the lengths, but the angles were practically not affected. It is concluded that the postweaning Saimiri sciureus undergoes orthocephalization according to a general pattern already observed in rodents and suggested for pongids. Postweaning malnutrition affected growth in size but not shape changes related to the orthocephalization of the Saimiri skull.

Sexual dimorphism in schoolchildren of the Villa IAPI neighborhood (Quilmes, Buenos Aires, Argentina).

Villa IAPI is a poor neighborhood of about 5,000 inhabitants in the overpopulated conurbano bonaerense at the outskirts of the city of Buenos Aires. Most of the adult male residents are construction workers; the rest are temporary workers, underemployed, or unemployed. The inhabitants of Villa IAPI suffer the effects of many adverse socio-economic conditions, including poor nutrition, deficient sanitation, and inadequate medical care. Seven anthropometric variables were measured on 765 children from 6 to 14 years old to test for the presence of an altered pattern of sexual dimorphism. It was found that there were practically no sex differences in standing height and upper-arm muscle circumference. In some age groups, there was a weak but significant sexual dimorphism in body weight and sitting height. The greatest and most persistent dimorphism was found in head circumference, and in triceps and subscapular skinfolds. In all except two age groups, head circumference in males was significantly greater than in females. The other dimorphic variables (body weight, sitting height, and triceps and subscapular skinfolds) showed the opposite relationship. Essentially, females showed increments in subcutaneous fat, while reduced growth in muscle and bone was evident in males. The hypothesis of "better female canalization" can explain the altered dimorphic pattern found in the malnourished Villa IAPI population.

[Growth and sex dimorphism in school children according to their father's occupation]. / Crecimiento y dimorfismo sexual de escolares según la ocupación laboral paterna.

A cross-sectional morphometric study on 569 school children from the city of San Clemente del Tuyú (Buenos Aires, Argentina) has been performed. The sample was subdivided into 28 subgroups according to the age range (7-13 years old), sex, and occupational status -low or high- of the fathers. Body weight, height, sitting height, and head and arm circumferences were measured. Statistics of analysis of variance (ANOVA) and Tukey test for unequal sample sizes were performed at each stage of age. Both males and females belonging to the lower social status showed a general decrement in growth: shortening in leg length was evident. Since the girls from both occupational status showed -in general terms-hypothesis of "better canalization of the females" has been corroborated by the present work.

[Growth in school children of Villa IAPI (Quilmes, Buenos Aires, Argentina)]. / Crecimiento en escolares de Villa IAPI (Quilmes, Buenos Aires, Argentina).

Growth in schoolchildren of Villa IAPI--a poor neighborhood placed near Buenos Aires (Argentina)--were cross-sectionally studied. Six hundred and forty five--291 males and 354 females--children from six to twelve years old were weighed (W), and the standing (StH) and sitting (SiH) heights, the head (HC) and the arm (AC) circumferences, and the triceps (TS) an the subscapular (SS) skinfolds were measured. The muscular braquial circumference (MC), and the length of the inferior segment of the body (IS) were also calculated. All of the measurements were transformed to "z" scores. It was observed that in all cases--except for 11 year-old females--both W and StH were diminished. This trend was stronger in males than in females. Both SiH an HC did not show differences with respect to local growth standards. Skinfold values however, were always greater in Villa IAPI children--except SS in 9 to 12 year-old males, and in 12 year-old females--than those of normal standards, Such differential growth pattern suggests that two joined strategies--for protection and adaption to unbalanced environment--actually acted in the Villa IAPI population.

Sexual cranial dimorphism in malnourished rats treated with growth hormone.

One hundred and sixty two Holtzman rats of both sexes were malnourished during suckling and post-weaning periods. Some of them received periodic injections of growth hormone. After sampling, at 56 days of age, skulls were cleaned and measured. Differences within and between sexes were estimated by Mahalanobis D2 distances. Normal cranial differentiation between sexes (SCD) was decreased by malnutrition and restored by growth hormone treatment. The effect of the growth hormone on skull size was larger in malnourished males than females. This differential increment between sexes explains how growth hormone acted on the restoration of SCD.

The influence of gonadic hormones on skull differences in rats malnourished during lactation.

One hundred and twenty five Holtzman rats of both sexes were submitted to malnutrition during suckling with or without periodic injections of testosterone enantate in males and estradiol valerianate in females. Ten cranial measurements were made, and morphological differences within and between sexes were calculated by multivariate Mahalanobis D2-distances. Malnutrition delayed the cranial difference between sexes, which was restored by hormonal treatment. Testosterone arrested the skull size difference between sham and malnourished males. Estradiol stimulated the skull size difference between sham and malnourished females. This counteracting effect indicates that at early ages, both hormones stimulate sexual cranial dimorphism when a protein-calorie malnutrition acts on both sexes.

The influence of gonadic hormones on skull differences in rats malnourished during lactation.

One hundred and twenty five Holtzman rats of both sexes were submitted to malnutrition during suckling with or without periodic injections of testosterone enantate in males and estradiol valerianate in females. Ten cranial measurements were made, and morphological differences within and between sexes were calculated by multivariate Mahalanobis D2-distances. Malnutrition delayed the cranial difference between sexes, which was restored by hormonal treatment. Testosterone arrested the skull size difference between sham and malnourished males. Estradiol stimulated the skull size difference between sham and malnourished females. This counteracting effect indicates that at early ages, both hormones stimulate sexual cranial dimorphism when a protein-calorie malnutrition acts on both sexes.

The influence of gonadic hormones on skull differences in rats malnourished during lactation.

One hundred and twenty five Holtzman rats of both sexes were submitted to malnutrition during suckling with or without periodic injections of testosterone enantate in males and estradiol valerianate in females. Ten cranial measurements were made, and morphological differences within and between sexes were calculated by multivariate Mahalanobis D2-distances. Malnutrition delayed the cranial difference between sexes, which was restored by hormonal treatment. Testosterone arrested the skull size difference between sham and malnourished males. Estradiol stimulated the skull size difference between sham and malnourished females. This counteracting effect indicates that at early ages, both hormones stimulate sexual cranial dimorphism when a protein-calorie malnutrition acts on both sexes.

Changes in skull components of the squirrel monkey evoked by growth and nutrition: an experimental study.

Twenty weanling 6-month-old male squirrel monkeys were allotted to the following treatments: 1) first control animals were killed at weaning; 2) second control animals were killed when 24 months old; and 3) malnourished animals were fed on a low-protein diet and killed at age 24 months. Lateral and vertical teleradiographies were taken. Growth of the neurocranial and splanchnocranial components were measured by volumetric (size estimators) and morphometric (shape estimators) indices. All facial components grew. The neurocranial components showed a heterogeneous behavior: The anteroneural component remained stable, and the increase of the midneural component was compensated by a decrease in the posteroneural component. Malnutrition affected the growths of 1) the craniofacial complex, 2) the splanchnocranium, and 3) the respiratory and midneural components. Growth influenced skull shape through 1) increases of the splanchnocranium and the midneural component relative to the neurocranium; 2) decreases of the masticatory and optic components relative to the splanchnocranium, and 3) decreases of the anteroneural and posteroneural components relative to the neurocranium. Malnutrition influenced skull shape through the relationship between the anteroneural component and the neurocranium. These results confirmed the existence of functional interrelationships among the cranial components. A new approach to craniological studies is suggested.

Effect of gonadal activity on the cranial dimorphism of the rat.

Weanling rats of both sexes were submitted to either castration, or castration together with periodic injections of testicular extract to males or of ovarian extract to females. Control and experimental animals were sampled at 63 days of age. Cranial differentiation between sexes was estimated by Mahalanobis D2 distances. The controls showed a significant sexual cranial difference. Orchidectomy decreased cranial differences and this effect was compensated by injections of testicular extract. On the other hand, oophorectomy increased cranial differences, which were diminished by injections of ovarian extract. Sexual cranial dimorphism in the normal rat seems to be the result of a counteracting effect between testicular and ovarian hormonal secretions.

Studies on orthocephalization: growth behavior of the rat skull in the period 13-49 days as described by the finite element method.

Rat cranial skeletal growth was studied, using a cross-sectional data set, for the period 13-49 days by the application of the concepts of continuum mechanics and the numerical techniques of the finite element method (FEM). In contrast to the methods of conventional craniometry (CM) and roentgenographic cephalometry (RCM) the FEM permits fine scale, reference frame invariant descriptions and analysis of growth behavior. This advantage was demonstrated by a numerical example of the use of FEM. The skull was discretized into a number of two-dimensional, triangular elements, whose enclosed areas corresponded closely to both specific skeletal structures and to related functional matrices. Since it was assumed presently that the growth behavior of all of the points enclosed within a given element was similar, the application of the functional matrix hypothesis permitted an integrated description of the growth of the skeletal structure and functional matrix related to each element. The principal locus of rotation of the facial skull, relative to the cranial base, is the inferior frontoethmoidal articulation, a motion that includes a rigid body rotation. Other active and passive skeletal and visceral growth events associated with orthocephalization were located and described. Finally it was shown that the morphogenetically important growth behavior of other portions of the rat head were not directly involved in orthocephalization.