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PubMed1990

Calcitonin gene-related peptide and somatostatin immunoreactivities in the rat lumbar spinal cord: sexually dimorphic aspects.

The immunohistochemical distribution of calcitonin gene-related peptide and somatostatin in rat lumbar spinal laminae VII-X was investigated using the peroxidase-antiperoxidase technique. Within L1,2 laminae VII and X, calcitonin gene-related peptide and somatostatin fibers demarcate the location of preganglionic sympathetic neurons in a similar fashion in either sex but somatostatin is distributed in a sexually dimorphic manner in the lumbosacral (L5-S2) spinal cord with the male rat containing more somatostatin fibers and neurons than females. Within the ventral horn (lamina IX), calcitonin gene-related peptide has a sexually dimorphic distribution. Calcitonin gene-related peptide varicose fibers are found within the sexually dimorphic male cremaster nucleus but are virtually absent in the female cremaster nucleus. Calcitonin gene-related peptide varicose fibers are nearly absent in the remainder of the male and female lamina IX: this area includes the other two known sexually dimorphic spinal motonuclei: the dorsomedial and dorsolateral nuclei. Virtually all motoneurons in the lumbosacral spinal cord which are not sexually dimorphic contain calcitonin gene-related peptide. However, calcitonin gene-related peptide containing motoneurons have a heterogeneous distribution within sexually dimorphic nuclei. Calcitonin gene-related peptide containing motoneurons within the male and female cremaster nucleus are extremely rare. Some motoneurons within the male and female dorsomedial and dorsolateral nuclei contain calcitonin gene-related peptide with the female dorsomedial and dorsolateral nuclei containing a greater percentage of calcitonin gene-related peptide-containing motoneurons (c. 50%) than males (c. 20%). Somatostatin fibers are preferentially located in sexually dimorphic nuclei of either sex and are distributed in a sexually dimorphic manner within these nuclei with males containing a greater amount of somatostatin fibers than females. The amount of somatostatin immunoreactivity is most dense in the medial aspect of the dorsolateral nucleus, dense in the dorsomedial nucleus, moderate in the cremaster nucleus, and sparse in the lateral portion of the dorsolateral nucleus. In addition, a small column of motoneurons, between the dorsomedial and dorsolateral nuclei at the L5 level, is outlined by somatostatin fibers in females but is absent in males. Somatostatin containing motoneurons were not observed within the lumbar sexually dimorphic nuclei of either sex.

Animals↗
PubMed2000

Sexual dimorphism in relation to current selection in the house finch.

Sexual dimorphism is thought to have evolved in response to selection pressures that differ between males and females. Our aim in this study was to determine the role of current net selection in shaping and maintaining contemporary sexual dimorphism in a recently established population of the house finch (Carpodacus mexicanus) in Montana. We found strong differences between sexes in direction of selection on sexually dimorphic traits, significant heritabilities of these traits, and a close congruence between current selection and observed sexual dimorphism in Montana house finches. Strong directional selection on sexually dimorphic traits and similar intensities of selection in each sex suggested that sexual dimorphism arises from adaptive responses in males and females, with both sexes being far from their local fitness optimum. This pattern is expected when a recently established population experiences continuous immigration from ecologically distinct areas of a species range or as a result of widely fluctuating selection pressures, as found in our study. Strong and sexually dimorphic selection pressures on heritable morphological traits, in combination with low phenotypic and genetic covariation among these traits during growth, may have accounted for close congruence between current selection and observed sexual dimorphism in the house finch. This conclusion is consistent with the profound adaptive population divergence in sexual dimorphism that accompanied very successful colonization of most of the North America by the house finch over the last 50 years.

Adaptation, Physiological↗
PubMed2003

Sexual dimorphism and adaptive speciation: two sides of the same ecological coin.

Models of adaptive speciation are typically concerned with demonstrating that it is possible for ecologically driven disruptive selection to lead to the evolution of assortative mating and hence speciation. However, disruptive selection could also lead to other forms of evolutionary diversification, including ecological sexual dimorphisms. Using a model of frequency-dependent intraspecific competition, we show analytically that adaptive speciation and dimorphism require identical ecological conditions. Numerical simulations of individual-based models show that a single ecological model can produce either evolutionary outcome, depending on the genetic independence of male and female traits and the potential strength of assortative mating. Speciation is inhibited when the genetic basis of male and female ecological traits allows the sexes to diverge substantially. This is because sexual dimorphism, which can evolve quickly, can eliminate the frequency-dependent disruptive selection that would have provided the impetus for speciation. Conversely, populations with strong assortative mating based on ecological traits are less likely to evolve a sexual dimorphism because females cannot simultaneously prefer males more similar to themselves while still allowing the males to diverge. This conflict between speciation and dimorphism can be circumvented in two ways. First, we find a novel form of speciation via negative assortative mating, leading to two dimorphic daughter species. Second, if assortative mating is based on a neutral marker trait, trophic dimorphism and speciation by positive assortative mating can occur simultaneously. We conclude that while adaptive speciation and ecological sexual dimorphism may occur simultaneously, allowing for sexual dimorphism restricts the likelihood of adaptive speciation. Thus, it is important to recognize that disruptive selection due to frequency-dependent interactions can lead to more than one form of adaptive splitting.

Adaptation, Biological↗
PubMed1992

Sexual dimorphism in newborns and adults.

A total of 1034 newborns were used to analyze sexual dimorphism with respect to 37 somatic traits and ratios between them, describing body shape. Arithmetic means and standard deviations were calculated for both sexes. Similarly, sexual dimorphism of adults was analyzed. Sexual differences in newborns were statistically significant for most measurements but only for some body proportions (relative chest size, foot shape, relative lower extremity length, and the ratio of head to chest circumference). The highest degree of sexual dimorphism in newborns was shown by the index standardized on the mean (dsex/mean) of such traits as the thickness of subcutaneous fat tissue on the thigh, subscapular fat tissue and fat tissue on the 10th rib, body weight, hand breadth, and relative chest size (Marty index). A moderate dimorphism was found for the length of upper extremities, forearm with the hand, head with the neck, hand and trunk, the size of the nose and foot, the breadth of hips and mandible, and the upper-face height. A low dimorphism was found for body length, circumference and breadth of head, face diameter, chest circumference, foot shape, relative length of lower extremities, and proportion between head and chest circumferences. Sexual differences (dsex/mean) for all the somatic traits examined in adults were statistically significant. The dimorphism of all the traits (except hip breadth) was higher in adults than in newborns. The highest increase in sexual dimorphism was noted for chest breadth (ca 55 times), then for chest depth (ca 17 times), thickness of subcutaneous fat tissue on arm (ca. 17 times), and the length of lower extremities (ca 15 times). Sexual differences in proportions (shape) of the body were also better pronounced in adults than in newborns. Sexual dimorphism standardized for dispersion (dsex/SD) in newborns differed from that in adults with respect to the degree of its expression and the sequence of the traits showing the highest and the lowest levels of dimorphism. This results from intra-group variation of different traits.

Adipose Tissue↗
PubMed1994

Experimental perturbation of the development of sexual size dimorphism in the mouse skeleton.

BALB/c mice were raised for 30 days under nine treatment regimens to determine their effects on sexual dimorphism for size of the femur and of the body. Treatment groups were divided into three experiments: 1) burrowing in a high litter cage; eight times normal gravity for a total of one hour per day; a voluntary exercise control. 2) Unilateral femoral and sciatic nerve ablation; the opposite unoperated leg. 3) Swimming exercise; anabolic steroid; swimming and anabolic steroid; normal exercise control. Traits measured were body weight gain and thirteen femoral characters: moment at failure, length, cross-sectional area, anteroposterior and lateromedial diameters of the cross section, wall thickness for all four quadrants of the shaft, moments of inertia of the cross section in the anteroposterior and lateromedial directions, deflection of the shaft before failure, and total mineral content. Sexual dimorphism of the traits studied varied significantly with treatment. The greatest dimorphism was seen in the controls and the burrowing group. The least dimorphism was seen in the eight times gravity, the steroid, and the exercise and anabolic steroid groups. Reduction in the extent of sexual dimorphism was not correlated with a reduction in the loading regimen but rather seemed mediated by systemic changes in physiology brought on by several factors. Change in the amount of sexual dimorphism for size from the control reflects change in growth rates for males and females in response to different treatments. Change in growth rates of juvenile males and females will likely result in changes in the size of femoral characters and body weight in the adult. Change in the size of femoral characters affects the strength of the femur. In natural populations, a change in the body size of adult males and females could adversely affect reproductive success in groups that normally exhibit strong dimorphism, and hence, select against any conditions that reduce sexual dimorphism. Ordinarily, a significant change in sexual dimorphism--of the magnitude seen here--through natural selection, would take several generations.

Animals↗
PubMed1992

Sexual dimorphism in the human bony pelvis, with a consideration of the Neandertal pelvis from Kebara Cave, Israel.

Sexual dimorphism of the human pelvis is inferentially related to obstetrics. However, researchers disagree in the identification and obstetric significance of pelvic dimorphisms. This study addresses three issues. First, common patterns in dimorphism are identified by analysis of pelvimetrics from six independent samples (Whites and Blacks of known sex and four Amerindian samples of unknown sex). Second, an hypothesis is tested that the index of pelvic dimorphism (female mean x 100/male mean) is inversely related to pelvic variability. Third, the pelvic dimensions of the Neandertal male from Kebara cave, Israel are compared with those of the males in this study. The results show that the pelvic inlet is the plane of least dimorphism in humans. The reason that reports often differ in the identification of dimorphisms for this pelvic plane is that both the length of the pubis and the shape of the inlet are related to nutrition. The dimensions of the pelvis that are most dimorphic (that is, female larger than male) are the measures of posterior space, angulation of sacrum, biischial breadth, and subpubic angle. Interestingly, these dimensions are also the most variable. The hypothesis that variability and dimorphism are inversely related fails to be supported. The factors that influence pelvic variability are discussed. The Kebara 2 pelvis has a spacious inlet and a confined outlet relative to modern males, though the circumferences of both planes in the Neandertal are within the range of variation of modern males. The inference is that outlet circumference in Neandertal females is also small in size, but within the range of variation of modern females. Arguments that Neandertal newborns were larger in size than those of modern humans necessarily imply that birth was more difficult in Neandertals.

Animals↗
PubMed2005

Ontogenetic bases of canine dimorphism in anthropoid primates.

This study tests hypotheses regarding the ontogeny of canine tooth size dimorphism in five anthropoid primate species (Saguinus fuscicollis, Macaca mulatta, Cercocebus atys, Papio hamadryas, and Mandrillus sphinx). Canine measurements and chronological age data are analyzed to determine if bimaturism, a sex difference in the age at which eruption ceases, accounts for canine tooth sexual dimorphism. Canine height measurements are evaluated through a variety of regression techniques. Results show a lack of sexual dimorphism in Saguinus. While size dimorphism is absent in the deciduous teeth of all species analyzed, the adult teeth in cercopithecines become increasingly dimorphic through ontogeny. Female adult tooth eruption regularly precedes male tooth eruption, and regression-based eruption trajectories for both sexes intersect at about the age at which the female tooth reaches adult size. Males erupt the tooth later and more rapidly than females. Males also reach a larger adult size than females by erupting the tooth for much longer periods of time. Bimaturism is primary in the production of dimorphism, but rates of eruption show modest variation. These results point to the scheduling of sexual selection through intermale competition as a primary factor determining male eruption timing, rates of eruption, and adult size. Life history factors may play a role in determining the relations between the scheduling of intrasexual competition and canine eruption. Female contributions to sexual dimorphism are apparent in these species, suggesting that similar levels of dimorphism can be attained through diverse ontogenetic pathways.

Age Factors↗
PubMed1996

c-Fos immunoreactivity in the sexually dimorphic area of the hypothalamus and related brain regions of male gerbils after exposure to sex-related stimuli or performance of specific sexual behaviors.

The sexually dimorphic area of the gerbil hypothalamus is essential for male sex behavior. To determine which aspects of mating activate its cells, or cells near or connected to it, we visualized c-Fos in the brains of male gerbils that had been exposed to various types of sex-related stimuli or that had displayed various aspects of sex behavior. Five groups of males were placed in familiar arenas containing sex-related odors. All subjects had previously mated in these arenas. For four groups, a female was introduced and remained with the male until he ejaculated, intromitted, mounted or sniffed her. Males in the fifth group remained in the arena alone. Males in a sixth group were placed in a clean arena in another room. These males were also familiar with this arena but had never encountered a female there. The seventh group remained in their home cages. The posterodorsal preoptic nucleus, the lateral part of the posterodorsal medial amygdala, the medial part of the sexually dimorphic area and the parvicellular part of the subparafascicular nucleus of the thalamus expressed c-Fos after ejaculation. Whether these cells triggered ejaculation or responded to it is not clear. The latter two areas also expressed c-Fos whenever males were exposed to the sex arena, but the sexually dimorphic area pars compacta did not express c-Fos under any condition. The medial core of the nucleus accumbens, the ventrolateral septum, the caudomedial bed nucleus of the stria terminalis, the medial/central part of the posterodorsal medial amygdala and the lateral part of the sexually dimorphic area also expressed c-Fos when males entered the sex arena. The ventrolateral part of the ventromedial nucleus of the hypothalamus expressed c-Fos whenever males were with females. None of the 31 areas studied responded to mounting or intromission, but the zona incerta, the amygdalohippocampal area, the lateral part of the sexually dimorphic area and the area lateral to the medial part of the sexually dimorphic area showed progressive increases in c-Fos expression as mating progressed. The area dorsal to the medial part of the sexually dimorphic area, the paraventricular nucleus of the hypothalamus, the ventral premammillary nucleus and the retrorubral field showed the same level of c-Fos expression when males were exposed to the non-sexual context as when they were exposed to the sexual one. While a projection to the retrorubral field from the sexually dimorphic area is critical for male sex behavior, the retrorubral field did not show a sex-related c-Fos response. The data suggest that brain regions involved in male sex behavior are involved in different aspects of it and that this can also apply to different subsets of cells in each area. The data also indicate that cells involved in mating do not necessarily show mating-related patterns of c-Fos expression. Thus, while c-Fos is useful for identifying areas involved in mating, or other behaviors, its characteristics could cause relevant areas to be overlooked.

Amygdala↗
PubMed2004

Developmental processes and canine dimorphism in primate evolution.

Understanding the evolutionary history of canine sexual dimorphism is important for interpreting the developmental biology, socioecology and phylogenetic position of primates. All current evidence for extant primates indicates that canine dimorphism is achieved through bimaturism rather than via differences in rates of crown formation time. Using incremental growth lines, we charted the ontogeny of canine formation within species of Eocene Cantius, the earliest known canine-dimorphic primate, to test whether canine dimorphism via bimaturism was developmentally canalized early in primate evolution. Our results show that canine dimorphism in Cantius is achieved primarily through different rates of crown formation in males and females, not bimaturism. This is the first demonstration of rate differences resulting in canine dimorphism in any primate and therefore suggests that canine dimorphism is not developmentally homologous across Primates. The most likely interpretation is that canine dimorphism has been selected for at least twice during the course of primate evolution. The power of this approach is its ability to identify underlying developmental processes behind patterns of morphological similarity, even in long-extinct primate species.

Animals↗
PubMed2006

The evolution of condition-dependent sexual dimorphism.

Theory suggests that the net benefit of allocating resources to a sexual trait depends both on the strength of sexual selection on that trait and on individual condition. This predicts a tight coevolution between sexual dimorphism and condition dependence and suggests that these patterns of within-sex and between-sex variation may share a common genetic and developmental basis. Although condition-dependent expression of sexual traits is widely documented, the extent of covariation between condition dependence and sexual dimorphism remains poorly known. I investigated the effects of condition (larval diet quality) on multivariate sexual dimorphism in the fly Telostylinus angusticollis (Neriidae). Condition determined the direction of sexual size dimorphism and modulated sexual shape dimorphism by affecting allometric slopes and/or intercepts of sexually homologous traits in both sexes. Although the greatest responses to condition manipulation were observed in male sexual traits, both sexual and nonsexual traits exhibited substantial variation in the nature and magnitude of condition effects. Nonetheless, condition dependence and sexual dimorphism were remarkably congruent: variation in the strength of condition effects on male traits explained more than 90% of the variation in the magnitude of sexual dimorphism, whether quantified in terms of trait size or allometric slope. The genetic mechanisms that give rise to multivariate sexual dimorphism in body shape thus function in a strongly condition-dependent manner in this species, suggesting a common genetic basis for body shape variation within and between sexes.

Animals↗
PubMed1991

Patterns of sexual dimorphism in body weight among prosimian primates.

Many primatologists believe that there is no sexual dimorphism in body size in prosimian primates. Because this belief is based upon data that came from only a few species and were largely flawed in some aspect of sample quality, I re-examined the extent of sexual dimorphism in body weight, using weights of 791 adult prosimians from 34 taxa recorded over the last 17 years at the Duke University Primate Center. There was no significant sex difference in body weight in 17 species, but males were significantly larger in Nycticebus pygmaeus, Tarsius syrichta, Galago moholi, Galagoides demidovii, Otolemur crassicaudatus and Otolemur garnettii. Moreover, females were significantly larger in Microcebus murinus. Thus, the general lack of sexual dimorphism could be confirmed, notably for lemurs, but prosimians as a group show more variability in sexual size dimorphism than was previously thought. After including previously published data obtained in the wild from 8 additional species, I found significant heterogeneity in the degree of sexual dimorphism at the family level, but only the Indridae and Galagidae were significantly different from each other. Among the prosimian infraorders, the Lorisiformes were significantly more dimorphic than the Lemuriformes. Differences in dimorphism between higher taxonomic groups are discussed in the context of prosimian evolution, concluding that phylogenetic inertia cannot provide a causal explanation for the evolution of sexual dimorphism. The relative monomorphism of most prosimians may be related to allometric constraints and, especially in the Lemuriformes, to selective forces affecting male and female behavioral strategies.

Analysis of Variance↗
PubMed2005

Sexually dimorphic synaptic organization of the medial amygdala.

The medial amygdala is important in social behaviors, many of which differ between males and females. The posterodorsal subnucleus of the medial amygdala (MeApd) is particularly sensitive to gonadal steroid hormones and is a likely site for gonadal hormone regulation of sexually dimorphic social behavior. Here we show that the synaptic organization of the MeApd in the rat is sexually dimorphic and lateralized before puberty. With the use of whole-cell voltage-clamp recording and quantitative electron microscopy, we found that, specifically in the left hemisphere, prepubertal males have approximately 80% more excitatory synapses per MeApd neuron than females. In the left but not the right MeApd, miniature EPSC (mEPSC) frequency was significantly greater in males than in females; mEPSC amplitude was not sexually dimorphic. Paired-pulse facilitation of EPSCs, an index of release probability, also was not sexually dimorphic, suggesting that greater mEPSC frequency is caused by a difference in excitatory synapse number. Electron microscopy confirmed that the asymmetric synapse-to-neuron ratio and the total asymmetric synapse number were significantly greater in the left MeApd of males than of females. In contrast to results for excitatory synapses, we found no evidence of sexual dimorphism or laterality in inhibitory synapses. Neither the frequency nor the amplitude of mIPSCs was sexually dimorphic or lateralized. Likewise, the number of symmetric synapses measured with electron microscopy was not sexually dimorphic. These findings show that the excitatory synaptic organization of the left MeApd is sexually differentiated before puberty, which could provide a sexually dimorphic neural substrate for the effects of hormones on adult social behavior.

Amygdala↗
PubMed1989

[Dimorphism in fungi--a gray zone for taxonomy?].

Dimorphic fungi can grow as mycelial phase and as yeast phase. The change of growth form is effected by an altered programme in gene expression, which is induced either in certain stages of ontogenesis or by environmental factors. Therefore it is necessary to distinguish ontogenetically conditioned (irreversible) and environment conditioned (reversible) dimorphism. The first is characteristic for dimorphic Ustomycetes, Basidiomycetes and related anamorphs as well as for Taphrinales; the second for the majority of dimorphic Ascomycetes, Endomycetes, and related anamorphs. The integration of dimorphic fungi in the systems of filamentous fungi and of yeasts--which originally have been elaborated rather independently--was difficult in many cases. In recent times, the study of certain ultrastructural and biochemical-physiological characters has much facilitated the taxonomic arrangement of dimorphic fungi and has allowed to demonstrate some phylogenetic relations among filamentous, dimorphic, and yeast fungi. The authors hold the concept that yeasts have evolved from filamentous resp. dimorphic fungi by neotenic simplification.

Fungi↗
PubMed1998

Salivary gland sexual dimorphism: a brief review.

The term "sexual dimorphism" refers to any differences in form, whether those differences be morphological, chemical, or physiological in nature. Sexual dimorphism may be manifested as differences in size, morphological appearance, metabolic activities, responses to hormones, drug sensitivity, rates of maturation, etc. The first report, in 1940, of a sexual dimorphism of salivary glands was that of morphological differences between the submandibular glands (SMG) of male and female mice. The sexual dimorphism of the mouse SMG is probably the most widely studied sexual dimorphism of salivary glands. The sexual dimorphism of the mouse SMG has been examined using nearly all methods of study--from neuroanatomical studies of the adrenergic stimulation of secretion by these glands to electrophoretic analysis yielding zymograms of enzymes present in mouse SMG extracts. In addition to a brief review of the sexual dimorphism of the mouse SMG, this report will examine some less well-known examples of salivary gland sexual dimorphism.

Animals↗
PubMed2005

Ontogeny of craniofacial sexual dimorphism in the orangutan (Pongo pygmaeus). I: face and palate.

The orangutan is widely recognized as a highly dimorphic species. An ontogenetic approach to the study of sexual dimorphism can assist researchers in understanding both where and when these differences develop. In this study, 357 orangutans from Borneo were divided into five developmental stages representing infancy to mature adulthood. Three-dimensional (3D) coordinate data from 16 landmarks representing the face and palate were analyzed by means of a Euclidean distance matrix analysis (EDMA), a quantitative method for the comparison of forms. Three separate analyses (an age-specific static comparison of forms, a sex-specific analysis of growth trajectories, and an intersex comparison of patterns of relative growth) were carried out with the intent to describe the rate, timing, magnitude, and pattern of growth in the orangutan face and palate. The results indicate that generally males and females share a similar, but not identical, pattern of growth or local form change, but differ in growth rate, timing, and magnitude of difference. Dimorphism in the face and palate can be localized in infancy and traced throughout all age intervals. Orangutan females grow slightly faster than males from infancy to adolescence, at which time male growth exceeds female growth. Female growth ceases with the advent of adulthood, while male growth continues (i.e., both the number and magnitude of the dimorphic dimensions increase). Males and females are similar in facial dimensions and growth related to the orbits, upper face, and palate width. They maintain these similarities throughout development. However, they differ in facial and nasal height, palate length, snout projection, depth of the nasopharynx, and hafting of the face onto the skull. The face broadens and the zygomatic bone flares dramatically in adult males, corresponding to the development of cheek pads. While growth patterns are similar between the two sexes, they differ in the lateral orbit, snout projection, and hafting of the face onto the cranium. Adult dimorphism is the result of growth patterns experienced throughout life, and it is not equally expressed across the cranium. An understanding of patterns of dimorphism, along with the magnitude of difference, may be helpful for interpreting dimorphism in the fossil record.

Animals↗
PubMed2002

Population variation in second metacarpal sexual size dimorphism.

This paper contrasts levels of sexual size dimorphism in second metacarpal osteometric and geometric morphology in two bioculturally distinctive populations: 19th century Euro-Canadian settlers, and proto/historic central Canadian Inuit. Significant within-group sexual size dimorphism is found for all variables, though few show significant interpopulation differences. However, in every case the Euro-Canadian sample is more dimorphic than the Inuit sample. Notably, differences reside in geometric measures (total area, Imax) sensitive to variation in functional strain, and thus are interpretable in light of proximate causal models, i.e., activity profiles distinct from generalized mode of subsistence. Other proximate factors, such as nutritional stress acting to diminish Inuit sexual size dimorphism, may also play a role. However, models often cited to explain dimorphism, such as marriage practice (e.g., polygyny) or division of labor situated in mode of subsistence, do not. The higher sexual size dimorphism in the 19th century settler sample belies the notion that technological progress inevitably leads to reduced dimorphism.

Anthropology, Physical↗
PubMed1981

Sexual dimorphism and allometry in primate ossa coxae.

Five measurements were taken on the ossa coxae of 454 adult primates representing Ceboidea, Cercopithecoidea and Hominoidea. Sex differences in these variables and their relationships to overall body size and sexual dimorphism were tested by means of Student's T-test and regression analysis. The study attempts to clarify the nature of primate pelvic sexual dimorphism, including allometric effects, and more specifically, test the assertion made by Mobb and Wood (1977) that sexual dimorphism in body size in not an important determinant in pelvic sex differences. Variables that contribute to the size of the birth canal tend to be larger in females than males in all taxa studied except two. In these, Hylobates and Alouatta, there were no significant differences between the sexes for any of the five variables. In general, sexual dimorphism in variables contributing to the size of the birth canal was correlated (r approximately or equal to 0.8) with sexual dimorphism in body size. Furthermore, the coefficients of allometry underlying pelvic sex differences were shown to be moderately correlated (r approximately or equal to 0.5) with sexual dimorphism in size. The influence of other adaptive factors on primate pelvic sexual dimorphism are also briefly discussed.

Animals↗
PubMed1992

Corpus callosum in sexually dimorphic and nondimorphic primates.

The midsagittal area and other morphological measures were taken on the corpus callosum of four different species of primate: Macaca mulatta, M. fascicularis, Callithrix jacchus, and Saguinus oedipus. The first two species are strongly dimorphic, whereas the New World forms show little dimorphism with regard to overall body size, canines, and brain weight. Neither total corpus callosal area (TOTALCC), or other parts of the corpus callosum (CC) showed any significant sexual dimorphism in any of the primate species sampled. Only in M. mulatta did a sexual dimorphism appear to be significant. In males of this species, the dorsoventral width of the splenium was larger than in females. In addition, the anterior commissure (ANTCOMM) evinced no sexual dimorphism in the different species. Brain weight was significantly dimorphic in only M. mulatta, and when ratio data were used to correct for brain weight, no significant differences were found in the corpus callosum. This is in contrast to Homo sapiens, where the relative size of the CC has been reported to be larger in females, and particularly so in the posterior, or splenial portion of the CC. Correlation coefficients were calculated for the various variables within each species. In general, most of the callosal measures are significantly inter-correlated, although the exact pattern varies for each species. Thus, unlike Homo sapiens, or pongids such as Gorilla and Pan, neither New nor Old World monkeys show any striking evidence for sexual dimorphism in the corpus callosum.

Animals↗