PubMed Health⌕ Search

Biomedical subjects

W Leutenegger

Publications and source records attributed to W Leutenegger.

At least 19 recordsLinked to original sources
PubMed1989

The ontogeny of sexual dimorphism in the cranium of Bornean orang-utans (Pongo pygmaeus pygmaeus): I. Univariate analyses.

Based on a homogeneous sample of 212 individuals spanning all postnatal age periods, we examine the ontogeny of cranial sexual dimorphism in Bornean orang-utans (Pongo pygmaeus pygmaeus) by means of univariate statistics. A distinct pattern emerges at the early juvenile stage and continues at all subsequent stages with males tending to exceed females in all cranial dimensions. In conjunction, starting at mid-juvenile stage, there is a strong tendency for an increase in number and strength of significant cranial sex differences, all of them in favor of males. Significant sex differences in the viscerocranium, reflecting stronger prognathism in males, emerge prior to those in the neurocranium. The total ontogenetic pattern of cranial sexual dimorphism in orang-utans is remarkably similar to that of gorillas, except that there is no evidence of a sex difference in timing of the adolescent growth spurt in the orang-utan. As for other catarrhine species (Wood 1976), male variance of cranial dimensions tends to be greater than that of females, thus lending support to Leutenegger & Cheverud's (1982, 1985) model on the evolution of character dimorphism by means of variance dimorphism.

Analysis of Variance↗
PubMed1989

The ontogeny of sexual dimorphism in the cranium of Bornean orang-utans (Pongo pygmaeus pygmaeus): II. Allometry and heterochrony.

Based on a homogeneous sample of 212 individuals spanning all postnatal periods, we examine the ontogeny of cranial sexual dimorphism in Bornean orang-utans (Pongo pygmaeus pygmaeus) by means of allometric analysis and in terms of heterochrony. The bivariate growth allometries of 20 cranial dimensions against basicranial length yield two major patterns. Confirming the null hypothesis, strong ontogenetic scaling, where growth regressions of both sexes fall along a single ontogenetic continuum, and where shape differences between adult males and females result from the extension of relative growth in the smaller females to larger size in males, is found in 10 cases. Ontogenetic scaling is particularly strong in proportions of (1) the neurocranium directly associated with brain size, (2) the orbital region, and (3) the dental arcade. In terms of heterochrony such a pattern most likely is the result of a process termed "time hypermorphosis", i.e. an extension of the growth period in time in males. The second major pattern seen in the remaining 10 cases shows a departure from ontogenetic scaling, with males exhibiting a significantly steeper slope than females. Departures from ontogenetic scaling, where size and shape are dissociated with adult males being disproportionately larger than adult females, are found in proportions of cranial regions directly associated with secondary sexual character development: prognathism, canine size, and cheek pad area. In terms of heterochrony such a pattern most likely is the result of a process termed "acceleration", i.e. the rate of shape change is increased in males.

Animals↗
PubMed1985

Sexual dimorphism in the postcranial skeleton of New World primates.

This study examines sexual dimorphism in 24 dimensions of the postcranial skeleton of four platyrrhine species: Callithrix jacchus, Saguinus nigricollis, Saimiri sciureus, and Cebus albifrons. The two callitrichid species show a relatively small amount of variation in the degree of sexual dimorphism among the different dimensions. Variation is considerably higher in the two cebid species as reflected by a mosaic pattern of sexual dimorphisms with males being significantly larger than females in some dimensions, and females significantly larger than males in others. In dimensions of the pectoral girdle and limb bones, males and females in each of the two cebid species are essentially scaled versions of each other, with males being peramorphic compared to females. This pattern is primarily the result of time hypermorphosis, i.e. an extension of the growth period in time in males. Rate hypermorphosis, i.e. an increase in the rate of growth in time in males, appears to play an additional role, however, in S. sciureus. By contrast, in dimensions of the true pelvis, sex differences in shape are dissociated from those in size. They are interpreted as the result of acceleration, i.e. increase in rate of shape change in females, as an adaptation to obstetrical functions. Interspecific analyses indicate positive allometry of mean degree of postcranial dimorphism with respect to body size. This coincides with previous findings by Leutenegger and Cheverud [1982, 1985] on the scaling of sexual dimorphism in body weight and canine size, and thus supports their model which posits selection on body size as the prime mover for the evolution of sexual dimorphism.

Aging↗
PubMed1982

Scaling of sexual dimorphism in body weight and canine size in primates.

Among primates sexual dimorphism in both body weight and canine size increases exponentially with increasing body size. This suggests that a full explanation of the variance in sexual dimorphism can only be attained if, in addition to sexual selection, parental investment, and various ecological factors, the influence of body size is taken into account. Positive allometry in both body weight dimorphism and canine size dimorphism is demonstrated to be associated with polygyny. In monogamous species the two dimorphisms not only remain constant throughout the size range but actually are minimal or lacking at any given body size.

Animals↗
PubMed1977

Neonatal-maternal weight relationship in macaques: an example of intrageneric scaling.

In the genus Macaca, represented by seven species, neonatal weight scales at a power of maternal weight of a = 0.49. This value is lower than those for subordinal and ordinal scaling of neonatal weight in primates (a = 0.63-0.78), but it is higher than the value for intrageneric scaling of brain weight in Macaca (a = 0.18). A causal interpretation is attempted for differing values of a at different taxonomic levels and between different organ systems.

Animals↗
PubMed1976

Metric variability in the anterior dentition of African colobines.

The anterior dentition of three species of African colobines (Colobus polykomos, C. badius, and C. verus) was investigated metrically and the results analyzed for three characters: (1)intraspecific tooth size relations, (2)sexual dimorphism, and (3)interspecific relations. Based on incisor size sequences C. polykomos and C. badius appear to be more closely related to each other than either is to C. verus. However, incorporating the results of a previous study on postcanine dentition the three species appear to be equally closely related. The magnitude of sexual dimorphism in canine size decreases from C. badius to C. verus to C. polykomos. Interspecific differences in the degree of canine size dimorphism may be attributed to differential intensities of male intrasexual selection; however, the interspecific differences in canine size dimorphism do not correspond to the interspecific differences in body size dimorphism.

Africa↗