Evidence Of Sexual Dimorphism Research Articles

Semiquantification of Hypothalamic GH-Releasing Hormone Output in Women: Evidence for Sexual Dimorphism in the Mechanism of the Somatopause

Semiquantification of Hypothalamic GH-Releasing Hormone Output in Women: Evidence for Sexual Dimorphism in the Mechanism of the Somatopause

Mental barbel and meristic variation in the Antarctic notothenioid fish Dolloidraco longedorsalis (Perciformes: Artedidraconidae) from the Ross Sea

A collection of 58 specimens of Dolloidraco longedorsalis from the southwestern Ross Sea was studied for intraspecific variation in the number of second dorsal and anal rays, number of vertebrae, and length and shape of the mental barbel – a key diagnostic and taxonomic character in this family. Ranges for meristics are compact and extend documented values to 13 for anal rays and 37 for vertebrae. There is a nearly twofold difference in the relative length of the mental barbel. There are no significant differences between the sexes in any meristic or morphometric feature. The terminal expansion of the barbel exhibits four types, documented with illustrations and histology: typical expanded form (43%), not expanded or tapered (33%), slightly expanded (22%), and large expansion (2%). There is no relationship between absolute and relative barbel length and sex or barbel type and sex. There is no relationship between barbel type and size of the specimen. Twenty-five percent of specimens have the epidermis of the terminal expansion arranged as broad ridges or mounds. The mental barbel of D. longedorsalis is therefore individually variable with no evidence of sexual dimorphism, and the type of barbel does not vary ontogenetically. Histological analysis of the barbel reveals that the terminal expansion consists of a thick epidermis and that dermal papillae are responsible for the pattern of surface projections sometimes present. The epidermis near the tip of the barbel is twofold thicker in specimens with a terminal expansion. The distal morphology of the barbel, whether straight or expanded, probably has little functional significance. The barbel is richly supplied with nerves and blood vessels and the core consists of pseudocartilage. The barbel is probably a somatosensory organ.

Coordinating the segregation of sister chromatids during the first meiotic division: evidence for sexual dimorphism.

Errors during the first meiotic division are common in our species, but virtually all occur during female meiosis. The reason why oogenesis is more error prone than spermatogenesis remains unknown. Normal segregation of homologous chromosomes at the first meiotic division (MI) requires coordinated behavior of the sister chromatids of each homolog. Failure of sister kinetochores to act cooperatively at MI, or precocious sister chromatid segregation (PSCS), has been postulated to be a major contributor to human nondisjunction. To investigate the factors that influence PSCS we utilized the XO mouse, since the chromatids of the single X chromosome frequently segregate at MI, and the propensity for PSCS is influenced by genetic background. Our studies demonstrate that the strain-specific differences in PSCS are due to the actions of an autosomal trans-acting factor or factors. Since components of the synaptonemal complex are thought to play a role in centromere cohesion and kinetochore orientation, we evaluated the behavior of the X chromosome at prophase to determine if this factor influenced the propensity of the chromosome for self-synapsis. We were unable to directly correlate synaptic differences with subsequent segregation behavior. However, unexpectedly, we uncovered a sexual dimorphism that may partially explain sex-specific differences in the fidelity of meiotic chromosome segregation. Specifically, in the male remnants of the synaptonemal complex remain associated with the centromeres until anaphase of the second meiotic division (MII), whereas in the female, all traces of synaptonemal complex (SC) protein components are lost from the chromosomes before the onset of the first meiotic division. This finding suggests a sex-specific difference in the components used to correctly segregate chromosomes during meiosis, and may provide a reason for the high error frequency during female meiosis.

The biology of banded (Lagostrophus fasciatus) and rufous (Lagorchestes hirsutus) hare-wallabies (Diprotodontia : Macropodidae) on Dorre and Bernier Islands, Western Australia

Sex ratio, reproduction, body condition and morphology of banded (Lagostrophus fasciatus) and rufous (Lagorchestes hirsutus) hare-wallabies were assessed on Dorre and Bernier Islands. Data are derived from 236 banded hare-wallabies and 161 rufous hare-wallabies captured between 1959 and 1999. The sex ratio of captured banded hare-wallabies tended to be female-biased (0.79: 1 male: female) but was not a significant departure from parity. In contrast, pouch young tended towards a male bias at 1.35: 1. Females produced 1–2 young per year. They were capable of producing young at 1000 g, but the incidence of females carrying pouch young or lactating increased from 39% for females of 1000–1400 g to 80% for females of 1401–1800 g, then decreased slightly to 76% for females >1800 g. Births occurred throughout the year but there was some indication of a decline in the latter half of the year. Captured banded hare-wallabies ranged in weight from 850 to 2300 g. Animals on Dorre Island were in significantly better body condition than those on Bernier Island, although this could be an artefact of their shorter pes length. There was no evidence of sexual dimorphism and no differences in morphological measurements taken, other than pes length, between the two island populations. The sex ratio of captured rufous hare-wallabies was close to parity at 0.99: 1 and for pouch young tended to be male-biased at 2: 1. The smallest female with young weighed 1215 g, but the incidence of females carrying pouch young or lactating increased from 43% for females of 1215–1660 g to 61% for females of 1661–2015 g and 100% for females >2015 g. Females carried pouch young in all months sampled (March–September) and one incidence of twinning was noted. Captured rufous hare-wallabies weighed 600–2550 g. Body condition was similar for males and females and between islands, but smaller females of reproductive age were in poorer body condition than larger females. There was no evidence of sexual dimorphism but pes lengths of animals on Dorre Island were significantly shorter, head lengths longer and tail lengths shorter, than those on Bernier Island. Rufous hare-wallabies appear to show regional variation in body size, being smaller in the wetter and warmer Tanami/Alice Springs region and larger on the drier and cooler Shark Bay islands.

Reproductive biology of the edible jellyfish Catostylus mosaicus (Rhizostomeae)

The reproductive biology of the jellyfish Catostylus mosaicus (Quoy and Gaimard 1824) (Scyphozoa: Rhizostomeae) was investigated in New South Wales, Australia. Medusae were gonochoristic. There was a 1:1 ratio of male and female medusae and there was no evidence of sexual dimorphism. Oocytes arose from the gastrodermis and maintained contact with the gastrodermis, via trophocytes, throughout gametogenesis. Spermatogenesis occurred within follicles that arose from invagination of the gastrodermis. Detailed sampling of gonads over a period of 3.25 yr in Botany Bay, and over 2.5 yr in Lake Illawarra, indicated that gametogenesis occurred almost continuously during the year. Oocytes were smaller, or were absent from the ovaries during 3 of the 4 winters sampled at Botany Bay and during all 3 winter periods sampled at Lake Illawarra. Comparisons were made with other locations, although these were sampled less frequently. When medusae were present at a location, similar trends were observed. The size at which medusae matured varied, but during non-winter periods and at two locations, all medusae exceeding 130 mm diam were considered mature.

Biology of the Sand Smelt, Atherina presbyter (Teleostei: Atherinidae), Off the Canary Islands (central-east Atlantic)

Atherina presbyter is a common fish off the Canary Islands. Age, growth, reproduction, and mortality of the species are studied based on sampling carried out from July 1995 to June 1996. The parameters of the total length–total weight relationship are: a=0.004521, and b=3.0771. Otoliths age readings indicate that the sampled population consists of four age groups (0–III years). The von Bertalanffy growth parameters for all individuals are: L∞=122 mm total length, k=0.79 year−1, and t0=−0.21 years. Individuals grow quickly in their immature first year, attaining approximately 60% of their maximum length. After the first year, the annual growth rate drops rapidly, because the energy is probably diverted to reproduction. It is a gonochoristic species with no evidence of sexual dimorphism. The gonad is present as a single diffuse testis in males and as a single discrete ovary in females. The overall ratio of males to females is not significantly different from 1:1. The reproductive period of the species is protacted (February to June). The peak of the reproductive effort occurs in April–May. The size at first maturity is 68 mm. The population is being heavily exploited.

A new specimen of Ankalagon (Mammalia, Mesonychia) and evidence of sexual dimorphism in mesonychians

ABSTRACT A new, relatively complete and well-preserved mandible and dentition of the mesonychian Ankalagon saurognathus from the early Paleocene (Torrejonian) of the San Juan Basin, New Mexico, provides evidence of sexual dimorphism in dentary depth and canine size in Mesonychidae. The new specimen has a particularly well-preserved postcanine dentition, and ml and m2 differ little in morphology or size from those in the holotype. The p3-p4 and m3 in the new specimen are smaller in length and width than in the holotype, but the size differences fall within the intraspecific range of variation exhibited in extant carnivorans. The holotype differs from the new specimen in having a canine that is approximately 1.5 times greater in length and width, as well as a dentary that is substantially deeper and larger. It has been suggested that two other mesonychians, Hapalodectes and Dissacus, also exhibit sexual dimorphism but evidence for this remains equivocal. We discuss the phylogenetic and behavioral implications of this character.

Anatomy and systematics of the prosauropod dinosaur Thecodontosaurus antiquus from the upper Triassic of southwest England

ABSTRACT Re-examination of the surviving specimens of Thecodontosaurus antiquus indicates that this plesiomorphic sauropodomorph can be diagnosed on the basis of elongate basipterygoid processes, a relatively short dentary, and a squared posterior process of the ilium. Although much of the original topotype material found in the 1830s in Bristol, England, has now been lost, some 245 specimens remain. These indicate a small, gracile prosauropod, up to 2.5 m in length, distinguished primarily on the absence of derived characters seen in other prosauropods. Although attempts were formerly made to subdivide the Bristol specimens into several dinosaurian, and other, taxa, most appear to pertain to the prosauropod Thecodontosaurus antiquus. The specimens do indicate a clear separation into two morphs, a gracile and a robust form, presumably evidence of sexual dimorphism. A juvenile Thecodontosaurus sp. from South Wales may belong to the same species. A cladistic analysis indicates that Prosauropoda is probably a clade, rather than a series of outgroups to Sauropoda, but support for this conclusion is weak. Echoing other recent cladistic analyses, stronger support is found for the existence of a clade Sauropodomorpha, made up from Prosauropoda + Sauropoda, for the clade Sauropoda itself, and for the clade Eusauropoda within Sauropoda.

Mixed descending- and ascending-type thin limbs of Henle's loop in mammalian renal inner medulla.

Previous studies have generally indicated that the entire descending (DTL) and ascending thin limbs (ATL) of Henle's loops in the mammalian inner medulla exhibit structurally and functionally distinct properties. In the present study, we found that about 50% of Munich-Wistar rat inner medullary thin limbs, lying at positions distinctly above the bend, had segments exhibiting structural characteristics of DTL located immediately adjacent to segments exhibiting structural characteristics of ATL. Multiple DTL-type and ATL-type segments of variable length existed along a single straight portion of these mixed tubules. Inner medullary thin limbs with repeating, sequential expression of DTL-type and ATL-type regions were also numerous in Sprague-Dawley rats, mice, and rabbits with no evidence of sexual dimorphism. RT-PCR of microdissected segments showed that the water channel aquaporin-1 (AQP1) and the urea transporter UT-A2 were expressed in pure DTL, but not in pure ATL, and in DTL-type, but not in ATL-type, regions of mixed-type thin limbs. Immunocytochemistry revealed expression of AQP1 in cells of pure DTL, but not pure ATL, and in cells of DTL-type, but not ATL-type, regions of mixed-type thin limbs. In contrast, the chloride channel ClC-K1 was expressed in pure ATL, but not pure DTL, and in ATL-type, but not DTL-type, regions of mixed-type thin limbs. Discontinuous axial expression of AQP1, UT-A2, and ClC-K1 along the straight portion of single thin limbs indicates that these nephrons possess a more heterogeneous structure than previously recognized.

Sexual size and shape dimorphism in two species of newts, Triturus cristatus and T. vulgaris (Caudata: Salamandridae)

AbstractMorphometric data from Fennoscandian populations of the crested newt Triturus cristatus and the smooth newt Triturus vulgaris were analysed for the presence of sexual size and shape dimorphism. The data sets included nine body‐related and nine head‐related measurements and were examined with univariate, bivariate and multivariate methods. Sexual dimorphism was demonstrated in both species. The separation of specimens was highly related to sex. Although the expression of sexual dimorphism differed between the two species, some patterns were shared. These are discussed in terms of evolution of intersexual dimorphism according to models of ecology, fecundity and sexual selection. In multivariate analyses, sexual dimorphism was restricted to body‐related variables such as standard length and distance of extremities (with high values for females), contrasting against cloaca and limb‐related characters (with high values for males). In both species, the ‘distance of extremities’ measure (i.e. trunk length) was one of the strongest sexually dimorphic traits. No evidence of sexual dimorphism in head morphology was found. The results are interpreted as primarily concordant with theories on fecundity selection. For example, it has been suggested that females with larger trunk volumes increase their reproductive capacity. The fact that males had longer extremities, in relation to other characters measured, could be attributed to sexual selection. Long limbs in male newts may be beneficial for courtship performance. Since head‐related characters did not show any patterns of sexual dimorphism, no evidence was found to suggest that male and female crested and smooth newts have adapted to different feeding strategies.

Sexual size and shape dimorphism in two species of newts, Triturus cristatus and T. vulgaris (Caudata: Salamandridae)

Morphometric data from Fennoscandian populations of the crested newt Triturus cristatus and the smooth newt Triturus vulgaris were analysed for the presence of sexual size and shape dimorphism. The data sets included nine body-related and nine head-related measurements and were examined with univariate, bivariate and multivariate methods. Sexual dimorphism was demonstrated in both species. The separation of specimens was highly related to sex. Although the expression of sexual dimorphism differed between the two species, some patterns were shared. These are discussed in terms of evolution of intersexual dimorphism according to models of ecology, fecundity and sexual selection. In multivariate analyses, sexual dimorphism was restricted to body-related variables such as standard length and distance of extremities (with high values for females), contrasting against cloaca and limb-related characters (with high values for males). In both species, the ‘distance of extremities’ measure (i.e. trunk length) was one of the strongest sexually dimorphic traits. No evidence of sexual dimorphism in head morphology was found. The results are interpreted as primarily concordant with theories on fecundity selection. For example, it has been suggested that females with larger trunk volumes increase their reproductive capacity. The fact that males had longer extremities, in relation to other characters measured, could be attributed to sexual selection. Long limbs in male newts may be beneficial for courtship performance. Since head-related characters did not show any patterns of sexual dimorphism, no evidence was found to suggest that male and female crested and smooth newts have adapted to different feeding strategies.

Development of the Cerebral Cortex: XI. Sexual Dimorphism in the Brain

Do sexual differences in the organization of the brain exist, and if so, why? Are they caused by environment or genetics? In fact, the evidence for sexual dimorphism in the brain is compelling. In many animals, distinct differences between sexes in brain morphology have been found that are believed to be responsible for a number of the observed behavioral differences between the sexes. How do these differences arise and affect behavior? Many result from the differential expression of gonadal steroid hormones during early critical periods of brain development.

The medial preoptic and anterior hypothalamic regions of the rhesus monkey: cytoarchitectonic comparison with the human and evidence for sexual dimorphism

Examination of thionin-stained sections through the hypothalamus of the rhesus monkey revealed nuclei that resemble the first, second and third interstitial nuclei of the anterior hypothalamus (INAH1-3) of the human. Volumetric analysis of these nuclei in a small sample of monkeys suggests that the nucleus that resembles INAH3 is larger in males than in females. INAH1-3 have each been reported to be larger in men than in women and each has been considered as a potential candidate for homology with the much-studied sexually dimorphic nucleus of the preoptic area (SDN-POA) of the rat. Positional and cytoarchitectonic criteria suggest that of these nuclei, INAH3 and its potential counterpart in the rhesus monkey are the best candidates for homology with the SDN-POA. While the criteria employed in the present study may be used to suggest homologies, they are not adequate to confirm them. Confirmation of the homologies suggested here must rely on other considerations such as connectivity, neurotransmitter and peptide content, and function. It is hoped that the present report will stimulate interest in further examinations of the rhesus hypothalamus that will test both the suggested homologies and the evidence for sexual dimorphism.

Biphasic and Region-Specific MAO-B Response to Aging in Normal Human Brain

Variations of monoamine oxidases (MAO) A and B were studied during aging in 27 human subjects (age range 17–93 years) in 18 brain structures of temporal cortex, frontal gyrus, hippocampal formation, striatum, cerebellum, and brainstem. [ 3H]Ro41-1049 and [ 3H]lazabemide were used as selective radioligands to image and quantify MAO-A and MAO-B respectively by enzyme autoradiography. Postmortem delay or time of tissue storage did not affect MAO-A or MAO-B levels. There was, moreover, no evidence of sexual dimorphism. A marked age-related increase in MAO-B was observed in most structures. This increase started at the age of 50–60 years. Before this age, MAO-B levels were constant in all structures studied. MAO-B-rich senile plaques were observed in some cortical areas but they did not significantly influence the age-related MAO-B increase. Surprisingly, no age-related MAO-B changes were observed in the substantia nigra. In contrast to MAO-B, no clear age-related changes in MAO-A were observed, indicating an independent regulation of the two isoenzymes, also suggested by the cross-correlation analysis of these data.

Morphometric Analysis of Old World Talpidae (Mammalia, Insectivora) Using Partial-Warp Scores

We illustrate one approach to bridging the gap between the statistical methodology of multivariate morphometrics and the graphically oriented methods of geometric morphometrics for landmark data. Partial-warp scores (elements of the weight matrix from relative-warp analysis) are used as variables to describe nonaffine shape variation. The results of various multivariate analyses can then be visualized by reconstruction of images as weighted linear combinations of thin-plate splines. The method was applied to data on seven species of Old World moles of the family Talpidae. There was no evidence for sexual dimorphism or any interaction between sex differences and species differences. There were large statistically significant differences among species with respect to nonaffine shape differences (local deformations). Small but statistically significant differences were found among species with respect to the uniform component of shape variation. (Landmark data; geometric morphometrics; thin-plate spline; relative warps; Talpidae; Insectivora.)

Sexual dimorphism in Australian Echiniscus (Tardigrada, Echiniscidae) with descriptions of three new species

Abstract The presence of males in species of Echiniscus has been reported only as recently as 1987 and is still considered to be rare. However, males have been found to be common in a disproportionately large number of species of this genus found in Australia. Evidence of sexual dimorphism is presented for five species (three of which are new to science), females and males of which are differentiated on the basis of distinctive gonopores. In all five species males are shorter with longer clavae. Males of Echiniscus jamesi sp. nov., Echiniscus rodnae sp. nov. and Echiniscus curiosus sp. nov. have significantly longer claws. In E. rodnae sp. nov. and E. curiosus sp. nov. males have significantly longer lateral trunk appendages and the dorsal trunk appendage combinations of males of the latter are different from those of females. The widespread distribution of bisexual species of Echiniscus in xeric habitats in Australia does not support the current theory that parthenogenetic species are favoured in such environments.

Growth and nutrient digestibility by male and female Penaeus monodon: evidence of sexual dimorphism

Quadruplicate groups of 10 Penaeus monodon were grown in tanks in monosex and mixed-sex populations from 8.6 to 17.0 g (mean wet weight) over a period of 69 days. Measurements of feed intake and the apparent digestibility of dietary protein and energy were made in the second and tenth weeks of the experiment. Monosex female prawns grew significantly faster than monosex males and male prawns from mixed-sex tanks. The weight increment per moult of monosex females was greater ( P<0.05) than that of monosex males, but no difference in intermoult period was seen between any of the groups. Feed intake of monosex females tended to be greater than that of monosex males but not significantly so. No significant difference between the sexes was detected for either apparent digestibilities of dietary protein and energy or feed conversion.

Ultrastructural evidence of sexual dimorphism in supraoptic neurons: a morphometric study.

We have recently shown that in spite of the absence of receptors for gonadal steroids in the supraoptic nucleus (SON) of the rat hypothalamus, the volume of the nucleus and the size of its neurons are larger in males than in females, and that these differences between male and female rats are correlated with body weight and dependent on the vasopressinergic neurons. As supraoptic neurons and their organelles enlarge when they are engaged in active peptidergic secretion we have carried out a morphometric ultrastructural analysis to determine if cell structures involved in the synthesis and storage of neurosecretory material also display weight-dependent sex dimorphism. Groups of six male and six female rats aged 30, 60 and 180 days were used. Nucleoli, rough endoplasmic reticulum and neurosecretory granules were analysed and we estimated their volume or surface densities and the total volume of nucleoli and rough endoplasmic reticulum, and total surface area of rough endoplasmic reticulum. We found that, with the exception of neurosecretory granules, the densities of the organelles did not differ among the groups studied, but total values were higher in males. These differences were found to be weight-dependent. Since the organelles studied are regarded as reliable indicators of the neurosecretory activity of supraoptic neurons, our data fully support the view that the weight-dependent sexual dimorphism observed in this nucleus reflects greater synthetic activity of its vasopressinergic neurons associated with the need to maintain water balance in larger bodies.

Sex distribution in arrested precompacted human embryos

Evidence of sexual dimorphism before fetal gonadal differentiation in mammals has been accumulating, suggesting that male embryos develop faster than female ones. The current investigation was performed to evaluate whether the development rate of precompacted human embryos is controlled by sex chromosomes. Sex was determined by polymerase chain reaction and fluorescence in situ hybridisation in 172 arrested embryos derived from in vitro fertilisation. The sex ratio (1.02:0.98) did not differ significantly from 1:1. Although more males appeared to have greater fragmentation, the difference between the sex ratios of highly fragmented and normal embryos (1.08:0.92) was not significant. Arrested female embryos had a tendency to exhibit more than five nuclei and less than 10% fragmentation, but the trend was not statistically significant. The current results suggest that the first developmental block in human embryos occurs prior to and shortly after genomic activation and is not determined by the presence of the Y chromosome.

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.