Expression Of Sexual Dimorphism Research Articles

Diversity of sexual dimorphism in electrocommunication signals and its androgen regulation in a genus of electric fish, Apteronotus.

Gymnotiform electric fish emit an electric organ discharge that, in several species, is sexually dimorphic and functions in gender recognition. In addition, some species produce frequency modulations of the electric organ discharge, known as chirps, that are displayed during aggression and courtship. We report that two congeneric species (Apteronotus leptorhynchus and A. albifrons) differ in the expression of sexual dimorphism in these signals. In A. leptorhynchus, males chirp more than females, but in A. albifrons chirping is monomorphic. The gonadosomatic index and plasma levels of 11-ketotestosterone were equivalent in both species, suggesting that they were in similar reproductive condition. Corresponding to this difference in dimorphism, A. leptorhynchus increases chirping in response to androgens, but chirping in A. albifrons is insensitive to implants of testosterone, dihydrotestosterone or 11-ketotestosterone. Species also differ in the sexual dimorphism and androgen sensitivity of electric organ discharge frequency. In A. leptorhynchus, male discharge at higher frequencies than females, and androgens increase electric organ discharge frequency. In A. albifrons, males discharge at lower frequencies than females, and androgens decrease electronic organ discharge frequency. Thus, in both chirping and electric organ discharge frequency, evolutionary changes in the presence or direction of sexual dimorphism have been accompanied and perhaps caused by changes in the androgen regulation of the electric organ discharge.

Isolation and chronobiological analysis of a neuropeptide pigment-dispersing factor gene in Drosophila melanogaster.

In this article, the authors isolate a gene encoding a neuropeptide in Drosophila melanogaster. The substance is called pigment-dispersing factor (PDF), based on one of the roles it plays in crustaceans (the arthropods in which this factor was initially discovered). The PDF-encoding Drosophila gene (pdf) is intronless and present in a single copy per haploid genome. The cytological location of pdf is 97B on the third chromosome. The putative 102-amino-acid precursor (prepro-PDF) consists of a signal peptide and a PDF-associated peptide, followed by the mature PDF. The PDF-associated peptide region of the precursor is highly diverged from those of the crustacean precursors, whereas the primary structure of the mature PDF is conserved in other members of the pigment-dispersing hormone family. A single pdf transcript (ca. 0.8 kb) is expressed predominantly in the head; the expression levels of pdf mRNA are consistently higher in males than in females. Putative pdf homologous transcripts are present in other Drosophila species, which exhibit similar sexual dimorphic expression patterns. Cyclic expression of pdf over the course of the day and night was assessed, but the mRNA exhibited at best very gentle cycling. The pdf expression in two behaviorally arrhythmic mutants were examined; the expression was intact in a period0 mutant but absent in the disconnected mutant.

Sex chromosomes and human growth. A dental approach.

Studies on tooth crown size and structure of individuals with various sex chromosome anomalies and their normal male and female relatives have demonstrated differential direct effects on growth of genes on the human X and Y chromosomes. The Y chromosome promotes growth of both tooth enamel and dentin, whereas the effect of the X chromosome on tooth growth seems to be restricted to enamel formation. Enamel growth is decisively influenced by cell secretory function and dentin growth by cell proliferation. It is suggested that these differential effects of the X and Y chromosomes on growth explain the expression of sexual dimorphism in various somatic features, such as the size, shape and number of teeth, and, under the assumption of genetic pleiotropy, torus mandibularis, statural growth, and sex ratio. Future questions concern, among other topics, the Y chromosome and the mineralization process, concentric control of enamel and dentin growth, and gene expression.

Ontogeny and sexual dimorphic expression of mouse type 2 11 β-hydroxysteroid dehydrogenase

11 β-hydroxysteroid dehydrogenase (11 β-HSD) catalyzes the interconversion of cortisol to hormonally inactive cortisone (corticosterone (B) to 11-dehydrocorticosterone (A) in rodents), and as such is established as a pre-receptor signalling pathway for corticosteroid hormone action. To further evaluate the role of this enzyme in adult and fetal life we have characterized two isoforms of 11 β-HSD in mouse tissues. Mouse `liver' or type 1 11 β-HSD is a bi-directional dehydrogenase/oxo-reductase ( K m for B 1.9 μM, K m for A 0.73 μM). Oxo-reductase activity utilized only NADPH as a co-factor, whilst dehydrogenase activity increased with both NAD or NADP. Mouse `kidney' or 11 β-HS3D2 activity was NAD-dependent with a K m for B of 0.11 μM. Dexamethasone was not a substrate. Using an in-house mouse 11 β-HSD2 cDNA and NAD-dependent activity studies, 11 β-HSD2 was expressed in epithelial cells of colon, renal collecting ducts, ovary, and adrenal, but was absent in liver, spleen, testis and heart. With the exception of gonadal tissues, activity and mRNA levels were consistently higher in adult male versus female tissues. In fetal kidney and colon there was absent/low levels of 11 β-HSD2 expression from fetal day 15 to term (day 19/20). Placental 11 β-HSD2 mRNA and activity were highest on fetal day 13/14 and fell progressively to undetectable levels by term. Two isoforms of 11 β-HSD are present in mouse tissues in accordance with other mammalian species. The sexual-dimorphic expression 11 β-HSD2 in kidney and colon may reflect male-female differences in sodium homeostasis, and the absent expression of 11 β-HSD2 in late gestation may facilitate glucocorticoid-dependent maturation of mouse fetal tissues.

Phylogenies and Physiological Processes—The Evolution of Sexual Dimorphism in Southeast Asian Frogs

There are a number of species of Southeast Asian Rana that are characterized by an unusual suite of sexually dimorphic features and derived reproductive modes. These frogs lack the usual secondary sexual characteristics of ranid frogs: nuptial pads, vocal sacs, and enlarged flexor muscles. Secondary sexual characteristics in frogs are under androgenic control. Phyloge- netic analyses using morphological and molecular data indicate that a drop in androgen level and/or a shift in androgen sensitivity may have been involved in the evolution of male parental care and the loss of the common suite of secondary sexual characteristics in these Asian frogs. Phylogenetic analyses also provide important information on experimental design by indicating the most appropriate taxa to use in the exploration of physiological processes controlling the expression of sexual dimorphism. This work is an example of how emergent properties from phylogenetic analyses can be used to formulate and test hypotheses of process and pattern of evolutionary change. (Frog; Rana; hormone; sexual dimorphism; parental care.)

Sex- and tissue-specific expression of a cytochrome P450 2C2-luciferase transgene

To study the transcriptional regulation of the rabbit cytochrome P450 2C2 gene (CYP2C2), transgenic mice were generated using a DNA fragment containing the CYP2C2 5′-flanking region fused to a luciferase reporter gene. In one of three transgenic lines, this transgene was expressed in the liver and at a lower level in the kidney, similar to the tissue-specific pattern of this gene in rabbits. Unlike expression in rabbits, the transgene was expressed in a male-specific pattern in liver and kidney, and in the brain of both sexes. Expression of the transgene in male mice was repressed after castration, while expression in females was stimulated after testosterone treatment and periodic injection of rat growth hormone (GH). The expression of this transgene was also regulated developmentally in the liver. These results suggest that this 3500 bp of CYP2C2 5′-flanking region contains the basal transcriptional regulation elements for tissue-specific and developmental expression. Although a position effect can not be ruled out, this transgene may also include the cis-regulatory element for sexual dimorphic expression.

Estrogen Reduces Myointimal Proliferation After Balloon Injury of Rat Carotid Artery

Vascular disease progresses more slowly in females with functional ovaries than in males. The mechanisms of this vasoprotective effect of female sex are incompletely understood. This study tested (1) whether there is a sex difference in the development of myointimal proliferation after balloon injury of the rat carotid artery in vivo, (2) whether this response is estrogen or androgen dependent, and (3) whether there is a sexual dimorphism in expression of the c-myc proto-oncogene in intact and/or damaged rat carotid arteries. Ten-week-old male and female Sprague-Dawley rats were either gonadectomized or studied intact. Gonadectomized rats of both sexes were implanted with estradiol, testosterone, or nothing (control) 3 days before vascular injury. Two weeks later, the rats were killed by overdose of pentobarbital, and the injured right and uninjured control left carotid arteries were fixed and subjected to morphometric analysis for evaluation of the degree of myointimal thickening. Separate groups of intact male and female rats were killed at 1 and 2 hours after vascular injury, and total RNA from injured and uninjured vessels was subjected to Northern blot analysis for assessment of steady state c-myc mRNA levels. Neointimal area and the ratio of neointimal to medial area were significantly less in intact female rats than in intact male rats (P < .05). Gonadectomy of female rats was associated with a greater increase in neointima formation after balloon injury than that observed in intact females (P < .05), but testosterone replacement did not further enhance this response. Estradiol treatment significantly inhibited myointimal proliferation after vascular injury in gonadectomized rats of both sexes (P < .05). Neither gonadectomy nor gonadectomy plus testosterone replacement altered the myointimal proliferative response to balloon injury in male rats. Steady state c-myc mRNA levels were detectable in undamaged carotid arteries in intact rats of both sexes and were significantly greater in males than in females; c-myc mRNA levels were increased in both sexes after carotid injury, but the response was significantly larger in magnitude and more rapid in males than in females. These data indicate that the sex difference in myointimal proliferation after vascular injury is estrogen dependent. C-myc gene expression is greater in the undamaged carotid artery of the male than in that of the female, and the responsiveness of this gene to balloon injury of the artery is more rapid and more robust in the male than in the female rat. These findings have direct implications for the prevention and treatment of vascular disease in humans.

Secondary Sexual Dimorphism and Phylogenetic Constraints in Bats: A Multivariate Approach

We develop a method to evaluate the degree to which particular morphological characteristics contribute to multivariate group differences in general and to secondary sexual dimorphism for size and shape in particular. In addition, we recommend a correlative approach to assess the degree to which the contribution of characters to group differences is consistent in different taxa. We apply both methods to a suite of 12 cranial characters obtained from populations of 18 species of bats in five families (Emballonuridae, Noctilionidae, Phyllostomidae, Vespertilionidae, and Molossidae) from Caatinga and edaphic Cerrado biomes of northeastern Brazil. As expected, a correlation usually does not exist between profiles of the importance of characters to sexual dimorphism from the two biomes if the taxa are monomorphic with regard to sex (e.g., Vampyrops lineatus, Artibeus lituratus , and Myotis riparia ); any differences between the sexes within a biome are a result of chance. In contrast, significant correlations between profiles of importance of characters to intersexual variation in the two biomes usually exist when species are dimorphic (e.g., Anoura geoffroyi, Carollia perspicillata, Glossophaga soricina, Phyllostomus discolor, Molossus molossus , and Artibeus planirostris ). Significant constraints on the expression of sexual dimorphism exist between populations of the same species; similar suites of characters are involved in intersexual variation if dimorphism exists. Such constraints appear inoperative at higher taxonomic levels. We hypothesize that once differentiation occurs at the specific level, coadapted gene complexes and genetic dynamics associated with epistasis, pleiomorphism, and linkage disequilibrium no longer constrain dimorphism in the same fashion as in the ancestral condition.

The differential expression of dental sexual dimorphism in subspecies ofColobus guereza

Data on dental sex differences in seven of the eight currently recognized subspecies of Colobus guerezareveals a range of expression of sexual dimorphism. Males of most subspecies are larger than females throughout the dentition and this is especially pronounced for the canines and P 3 For C. g. guerezaand C. g. gallarum,however, sex differences in the canines and P 3 are less pronounced and females are often slightly larger than males in noncanine dental measurements. C. guerezasspp. occupying comparable habitats express similarities in the degree of maxillary canine dimorphism. In addition, for those subspecies distributed above the equator, there is also a cline of decreasing maxillary canine dimorphism from west to east in a progressively more northern direction. This cline corresponds to the occupation of increasingly more arid habitats, and reduced dimorphism is the result of larger maxillary canine size in females. We propose that this pattern of sexual dimorphism is related to differences in the relative intensity of predation pressure, guereza social organization, and energetic considerations. That the mandibular canine does not exhibit a similar trend of sexual dimorphism suggests that larger maxillary canines in females may function as weapons.

Involvement of pituitary hormone in the sex-related regulation of hepatic epoxide hydrolase activity in mice.

The involvement of the pituitary gland in the expression of sex-related differences in the activities of epoxide hydrolase (EH) in liver was examined in hypophysectomized and neonatally monosodium L-glutamate (MSG)-treated male and female mice. In hypophysectomized mice, the hepatic microsomal EH activity of males and females increased considerably above those of the respective sham-operated controls, and the female activity exceeded that of the sham-operated males. The hypophysectomy caused a decrease in soluble EH activity in males, while the operation led to an elevation of the activity in females. Neonatal treatment with MSG resulted in marked increases of microsomal EH activity in males and females at adulthood and the activity was about 2 times that of the male control mice. Treatment of hypophysectomized males and females with growth hormone (GH) resulted in a significant decrease in microsomal EH activity below those of the corresponding hypophysectomized controls, while the hormone treatment had no effect on the soluble enzyme activities. These results suggest that murine hepatic microsomal EH activity is principally under the suppressive control of the pituitary and GH is a causal hormone involved in the expression of sexual dimorphism in the enzyme activity.

Sexual dimorphism in cordylid lizards: a case study of the Drakensberg crag lizard, Pseudocordylus melanotus

In a high-altitude population of the Drakensberg crag lizard, Pseudocordylus melanotus, most adult males, unlike adult females, are brightly coloured, and they are larger in body size and have relatively larger heads than females. Three basic colour phases can be distinguished among the brightly coloured adult males. No apparent differences in reproductive activity, number and differentiation state of the generation glands and femoral pores, or scar frequency were noted among the three colour phases. In males the development of bright colours and the differentiation of the epidermal glands coincide with the onset of sexual maturity. Sexual dimorphism in head size of adults is due to a decrease in female head size relative to juvenile head size as well as an increase in relative head size of males. Preliminary data indicate a social structure of territorial polygyny in P. melanotus and suggest that the dimorphism can partly be ascribed to sexual selection. There are also, however, indications of altitudinal variation in the expression of sexual dimorphism, which may be explained in terms of differential energy allocation by females at different altitudes.

Early postnatal estrogen organizes sex differences in the extinction of a CRF running response

In the present study the organizational effects of sex steroids on the sexually dimorphic extinction of a continuously food-rewarded running response were investigated. Gonadally intact female rats neonatally treated from day 1 to day 8 of the postnatal life with estradiol benzoate (EB), dihydrotestosterone (DHT) or vehicle, and males treated in the same period with the antiandrogen ciproterone acetate (AC), the estrogen antagonist tamoxifen (TX) or vehicle were studied in adulthood during the acquisition and extinction phases of the response in a short and narrow runway. No difference in performance between groups was obtained in the response acquisition. However, during extinction control males extinguished faster than control females. DHT treatment to females and neonatal CA administration to males had no effect on the expression of sexual dimorphism. Conversely, TX administration to the males increased male's resistance to extinction at the levels shown by control or DHT females, whereas the females treated with EB exhibited similar extinction rates to those observed in nonhormonal treated or CA males. This finding suggests that the organizational effect of testosterone on the sexually dimorphic behavior studied in the present report are mediated by testosterone conversion to estradiol throughout the aromatization pathway in the brain.

Vertebral body diameters and sex prediction.

As a direct consequence of the generally larger body size of the male, it is reasonable to expect the adult human vertebral column to display sexual dimorphism. However, there is a distinct paucity of literature concerning sex-related variation in vertebral dimensions. This study examines the accuracy with which sex may be predicted from vertebral body diameters. In a sample selected from a documental skeletal series, sex could be correctly assigned with an accuracy approaching 90%. This degree of sexual differentiation is of value for both the forensic and archeological identification of human skeletal remains. An interesting relationship was noted between the degree of expression of sexual dimorphism and the role of each area of the vertebral body in body weight transfer. The posterior aspect of the vertebral body is involved in the transmission of body weight both vertically and laterally from the transverse processes. This area was consistently less dimorphic than the anterior region of the vertebral body, which is more concerned with the transfer of body weight from the vertebra above.

Evidence that the androgen receptor mediates sexual differentiation of mouse renal cytochrome P450 expression

We have previously shown that sexual dimorphism in the expression of mouse renal cytochrome P450s is mediated by androgens, probably at a transcriptional level [Henderson, Scott, Yang & Wolf (1990), Biochem. J. 266, 675-681]. In the present study we show that this effect is already observed for most isoenzymes at only 2-3 weeks of age, as is the ability to induce or suppress expression with exogenous testosterone. The testosterone responsiveness did, however, exhibit age- as well as dose-dependency. Intriguingly, the effects of androgen took up to 8 days to become maximized, and the dose of testosterone needed to convert the female into the male phenotype was much higher than the circulating levels normally found in males. Studies using testicular feminized (Tfm) male mice, which carry an androgen receptor defect, showed them to have the female kidney cytochrome P450 phenotype, and these animals were not responsive to testosterone treatment. These data demonstrate the involvement of the androgen receptor in the regulation process. Taken together, our results indicate that the androgen receptor does not interact directly with the P450 genes, but initiates a cascade of events leading to the changes in cytochrome P450 gene expression. Significant differences were observed in the degree of sexual dimorphism in kidney P450 expression in other mammalian species. The significance of these findings in relation to the observed sexual dimorphism in other species is discussed.

STRUCTURE AND SEXUAL DIMORPHIC EXPRESSION OF A LIVER-SPECIFIC RAT 3β-HYDROXYSTEROID DEHYDROGENASE/ISOMERASE

The enzyme 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase (3 beta-HSD) catalyzes the obligatory oxidation and isomerization of delta 5-3 beta-hydroxysteroid precursors into delta 4-3-ketosteroids which lead to the formation of all classes of steroid hormones. We report the molecular cloning of a third type of cDNA clone encoding rat 3 beta- HSD isolated from a rat liver lambda gt11 cDNA library. The nucleotide sequence of 1955 bp determined from overlapping cDNA clones predicts a protein of 372 amino acids which displays 80% similarity with that of rat type I and type II 3 beta-HSD proteins. RNA blot analysis reveals the presence of mRNA transcripts of 2.1 kb in male liver in contrast to the 1.7 kb mRNA species detected in adrenal and gonad poly(A)+ RNA. Ribonuclease protection assays using type I, type II and type III specific cRNA probes demonstrate the liver-specific expression of type III mRNA while the two others are expressed in adrenals and gonads. The type III mRNA species was below the detection limit in intact female liver while in hypophysectomized females, its accumulation was restored to 55% of the levels measured in intact or hypophysectomized male rats. The present data describe the presence of a third type of 3 beta-HSD mRNA species and its marked sexual dimorphic gene expression in the liver which apparently results from pituitary hormone-induced gene repression in female rat liver tissue.

Sexualhormonspiegel und Körperform bei den !Kung San. Ein Beitrag zur Erklärung der Pädomorphie sanider Populationen

In order to test the hypothesis that oestrogens as well as androgens modify the body shape resp. the paedomorphous habitus of !Kung San circulating levels of sex hormones (testosterone, 5 alpha-dihydrotestosterone, and oestradiol in the serum as well as free testosterone in the saliva) of 114 healthy !Kung San men from the Northern Kalahari of Namibia were quantitatively determined by means of the radioimmunoassay method. The probands were described by 50 body measurements and morphological characters like gynaecomastia. The results show that sex hormone concentrations and body shape are significantly correlated in !Kung San men as it has been previously demonstrated for non-African samples. This does not only refer to the expression of sexual dimorphism but also to the special aspect of paedomorphism. The hypothesis of Marrett, Davies and Tobias, however, that the paedomorphous type of the San is due to "over-oestrogenization" could not be confirmed. Rather, the comparatively low testosterone level of the !Kung San men seems to be of significance.

The evolution of sexual size dimorphism in prosimian primates.

The four major hypotheses advanced to explain the evolution of sexually dimorphic characters invoke sexual selection, natural selection, allometry, and phylogenetic inertia. In this paper, each of these hypotheses is examined for its usefulness in explaining the inter-specific variation in sexual size dimorphism among prosimian primates. Data on body weight and the degree of sexual dimorphism were obtained for 32 prosimian and 95 simian species. Although prosimians exhibited significantly less sexual dimorphism than simians, there was nevertheless significant variation in dimorphism among them. The degree of sexual dimorphism in prosimians did not show significant variance at any taxonomic level, but the majority of variance occurred within genera. Thus, sexual dimorphism in size among prosimians is probably not constrained by phylogeny at the generic level and above. There was no significant correlation between body size and the degree of sexual dimorphism in prosimians, suggesting the absence of an allometric effect. Similarly there was no relationship between body size and sexual dimorphism among simians in this size range. This result suggested that the expression of sexual dimorphism may nevertheless be influenced by absolute size. In prosimians, inter-specific differences in sexual dimorphism were not correlated with variance in male reproductive success. It is suggested that speed and agility of males, rather than size and strength, might have been favored by intra-sexual selection in most prosimians. It seems also plausible that the relative monomorphism of most prosimians, especially in the Lemuriformes, might be a result of increased female size favored by natural selection. Consideration of all natural and sexual selective pressures that affect size in both sexes separately is required to understand the adaptive function and evolution of primate size dimorphism.

Aspects of the reproductive biology of Gonostoma bathyphilum (Gonostomatidae)

Protandrous hermaphroditism among deep‐sea fishes is known only within one family, Gonostomatidae, and therein restricted to a few species of two genera, Cyclothone (C. atraria, C. microdon) and Gonostoma (G. elongatum, G. gracile). Gonostoma bathyphilum, the deepest dwelling (700–2700 m depth) of Gonostoma spp., is also protandrous and shares with Cyclothone spp. an expression of sexual dimorphism manifested by the excessive development of olfactory structures, including the olfactory lobes, in ripe males. Sex‐reversal in ripe males, therefore, involves a regression of these structures. The relationships apparent between sex, maturity and olfactory development, and those between animal size, maturity and depth of occurrence, indicate that whilst protandry is an integral component of the species' reproductive strategy some individuals develop directly as females and that among males (max. size 150 mm S.L.) sex‐reversal is not obligatory. Primary females, together with those derived from prematurely reversing males, may form an early maturing female group, spawning for the first time at about 110–120 mm S.L. Most hermaphrodites were &lt; 100 mm S.L., and within the 70–99 mm S.L. size‐range a significant proportion had mature male characters. Since males of this size were all found to be immature, this suggests that these hermaphrodites are derived from a precocious element within the initial male population, and, by virtue of size‐stratification by depth, are responsible for mating with the early‐maturing females. The lack of a marked seasonality in the sexual cycle implies an ever presence of all sexual categories within the population. It is conjectured that sex‐reversal of ripe males is a response to critical population density levels of ripe females and that the smaller, precocious males would be more prone to sex‐reversal than the larger, later‐maturing ones. In some respects protandry in G. bathyphilum is similar to that in G. elongatum. In the latter, however, the reproductive cycle is seasonally linked and sex‐reversal in males is probably obligatory. Even so, critical density levels of ripe females can still be invoked as being causal to sex‐reversal.

Morphometric variability in larvae of the Antarctic fly, Belgica antarctica (Diptera: Chironomidae)

Morphometric variability is examined in the larval head capsule of the midge Belgica antarctica Jacobs (Diptera: Chironomidae). This species is the southernmost free-living holometabolous insect and occurs over about a 650-km range on the western side of the Antarctic Peninsula. Highly significant differences were found between samples and between sexes for nine larval head capsule characters. No morphometric effect was found due to chromosomal inversion heterozygosity. The expression of sexual dimorphism was found to vary greatly between samples. Some samples exhibited no sexual dimorphism whereas others exhibited highly complex patterns of sexual dimorphism. Attempts to relate morphometric variability to geographic and ecological parameters met with only limited success. No correspondence was noted between the classification of samples based on inversion heterozygosity and that based on larval morphology.

The craniology and relationships of four species of Bos, : 4. The Relationship between Bos primigenius Boj. and B. taurus L. and its implications for the Phylogeny of the Domestic Breeds

The three previous papers in this series (Grigson, 1974, 1975, 1976) were a study of the basic craniology of the genus Bos using B. taurus as an example. This paper deals with B. primigenius from Holocene deposits in northern Europe, studying the relationship of absolute size, cranial proportions, angles and non-measurable characters to age and sex. It concludes that the two size forms of B. primigenius are merely the expression of sexual dimorphism, that the two forms B. primigenius and B. taurus are so similar that they form a continuum and should be considered to be of the same taxon, and that where B. taurus does differ from B. primigenius the differences can usually be ascribed to breed and can be described as specializations.