Ultrastructural events in horse gonadal morphogenesis.

The establishment and sexual differentiation of the gonads of horse embryos were studied using high-resolution techniques. The most dramatic observation is the early cytodifferentiation of the somatic cells into steroidogenic cells which takes place before sexual differentiation of the gonads. A unique morphogenetic pattern is established during this process: the seminiferous cords of the testis are completely segregated from the steroidogenic tissue by a basal lamina, while in the medulla of the ovary, steroidogenic cells differentiate inside the epithelial cords which contain germ cells. This early difference in the topographical distribution of steroidogenic cells favours the hypothesis that the interactions between somatic and germ cells vary with the genetic sex. The possibility of finding qualitative differences in steroidogenesis before and during sexual differentiation of the gonad suggests the horse gonad as a good model for the study of the role of the steroid hormones in the sexual differentiation of the mammalian gonad.     

P450 aromatase expression in the temperature-sensitive sexual differentiation of salamander (Hynobius retardatus) gonads

Sex differentiation of gonads in amphibians is believed to be controlled genetically, but altered epigenetically or environmentally. When larvae of the salamander Hynobius retardatus were reared at defined temperatures from hatching to metamorphic stages, a high temperature (28 degrees C) induced exclusively female gonads (ovaries), whereas intermediate (20 and 23 degrees C) or lower (16 degrees C) temperatures produced a 1:1 sex ratio of the morphological gonads. The thermosensitive period was determined to be restricted from 15 to 30 days after hatching, just before or when sexual differentiation occurred. Hynobius P450 aromatase (P450arom) cDNA was isolated from adult gonads and the partial nucleotide or deduced amino acid sequences were determined, showing a high level of identity with various vertebrate species. The P450arom gene was expressed predominantly in the adult ovary and brain, weakly in testis, but not in other somatic organs. A typical sexual dimorphism in P450arom expression was detected in normally developing larvae by a quantitative competitive RT-PCR; strong expression in the female gonads but very weak in male gonads. The dimorphism was detected much earlier than the morphological sexual differentiation of the gonads. When larvae were reared at the female-producing temperature (28 degrees C), strong expression was detected in all the temperature-treated larvae, suggesting that P450arom was up-regulated, even in genetic males. Our results confirm the importance of the P450arom regulation in the sexual differentiation of gonads and demonstrate that an up-regulation of P450arom is involved in the process of temperature-sensitive sex reversal in this species.     

Pattern and rate of ovary differentiation with reference to somatic development in anuran amphibians

The rate of somatic development of anuran amphibians is only roughly correlated with the rate of gonad differentiation and varies among species. The somatic stage of a tadpole often does not reflect its age, which seems to be crucial for gonad differentiation rate. We compared the morphology and differentiation of developing ovaries at the light and electron microscopy level, with reference to somatic growth and age of a female. Our observations were performed on 12 species of six families (Rana lessonae, R. ridibunda, R. temporaria, R. arvalis, R. pipiens, R. catesbeiana, Bombina bombina, Hyla arborea, Bufo bufo. B. viridis, Xenopus laevis, Pelobates fuscus) and compared with the results obtained by other authors. This allowed us to describe the unified pattern of anuran female gonad differentiation. Ovary differentiation was divided into 10 stages: I-III, undifferentiated gonad; IV, sexual differentiation; V, first nests of meiocytes; VI, first diplotene oocytes; VII-IX, increasing number of diplotene oocytes and decreasing number of oogonia and nests; X, fully developed ovary composed of diplotene oocytes with rudimental patches of oogonia. We distinguished three types of ovary differentiation rate: basic (most species), retarded (genus Bufo), and accelerated (green frogs of the subgenus Pelophylax genus Rana).     

QUANTITATIVE GENETICS OF SEXUAL DIMORPHISM IN HUMAN BODY SIZE

A classical data set is used to predict the effect of selection on sexual dimorphism and on the population means of three characters—stature, span, and cubit—in humans. Given selection of equal intensity, the population means of stature and of cubit should respond more than 60 times as fast as dimorphism in these characters. The population mean of span should also respond far more rapidly than dimorphism, but no numerical estimate of the ratio of these rates was possible. These results imply that sexual dimorphism in these characters can evolve only very slowly. Consequently, hypotheses about the causes of sexual dimorphism cannot be tested by comparing the dimorphism of different human societies. It has been suggested that primate sexual dimorphism may be an allometric response to selection for larger body size. We show that such selection can indeed generate sexual dimorphism, but that this effect is too weak to account for the observed relationship between dimorphism and body size in primates.     

Testicular differentiation and development in South American catfish,surubim, Pseudoplatystoma fasciatum

In the species Pseudoplatystoma fasciatum the males are smaller than females. Thus, the objective of this study was to describe the process of testicular differentiation and provide tools for sex manipulation techniques aimed at improving the productivity of farming of sexually‐reversed females. Correlation between the length, age, sex rate and the stage of gonadal development were analyzed in this species from samples collected between 0 and 240 days post‐hatching. Testicular differentiation was divided into eight stages, based on the cellular and morphological characteristics of the gonad. The results showed that sexual differentiation has a greater correlation to the size than the age in this species. This study provides knowledge on the proliferation and distinctive arrangement of somatic cells, which enabled the early identification of the testis due to the presence of future fringes in the specimens. Testicular differentiation in P. fasciatum was histologically different from other species due to the proliferation and distribution of somatic cells in the regions that would originate the testicular tubules and sperm ducts. Meiosis began at a later stage in comparison with other species, therefore, it was not considered a criterion for early sexual characterization. It can be concluded that testicular differentiation in P. fasciatum occurs relatively early and this data can be used to improve sex inversion protocols and increase productivity in this species.     

The influence of social factors on juvenile sexual differentiation in a diandric,protogynous grouper <Emphasis Type="Italic">Epinephelus coioides</Emphasis>

The influence of social factors on juvenile sexual differentiation was explored in a diandric, protogynous grouper Epinephelus coioides. Experimental social units were established as singles, pairs and quartets using sexually undifferentiated juveniles at an age of 22 weeks post-hatching (WPH); all gonads were examined histologically at 130 WPH, the age of first sexual maturation. The percentage of primary males was about 39% at the end of the experiment, higher than the <5% obtained under mariculture conditions or from wild stocks for similar age or body size. This study demonstrated for the first time that social factors can significantly influence juvenile sexual differentiation in E. coioides.     

Sex-specific somatic–otolith growth relationship in two Gadidae

Otolith and somatic mass of two Gadidae ( Merlangius merlangus and Trisopterus minutus ) were compared in order to analyse the sex-specific relationship between otolith and somatic growth at age. In the present study, otolith mass appeared a reliable indicator of age in both species. Otolith growth reflected somatic growth, but the relationship between these characters varied and differed between species and sexes.     

Chick gonad differentiation following excision of primordial germ cells

The differentiation of embryonic chick gonads lacking germ cells was compared to that of normal chick gonads to determine whether the somatic elements of sterile avian gonads will undergo normal sexual differentiation. Primordial germ cells were removed by surgical excision of anterior germinal crescent from early embryos, Hamburger and Hamilton stages 6–11. Surgically treated and control embryos were sacrificed at 6, 15, and 20 days of incubation, and their gonads were studied histologically. Analysis of differentiation was based on morphological criteria at the cellular, tissue, and organ levels. In both male and female embryos, the somatic elements of the gonads differentiated normally in the absence of germ cells. The significance of these results for understanding the controls of differentiation of both the somatic gonad and the germ cells in birds is discussed and correlated with similar results in mammals.     

Contrôle de la détermination et de la différenciation des caractères sexuels somatiques de Néréidiens (Annélides polychètes)

Résumé Les modalités de la détermination et de la différenciation du dimorphisme sexuel de Néréidiens (Annélides Polychètes) ont été recherchées chezNereis pelagica L. etPerinereis cultrifera G. par des expériences de décérébration, de castration (par irradiation X), de greffes et d'injection de produits génitaux.Les caractères sexuels somatiques des cirres parapodiaux (renflement et crénelures) se développent toujours conformément au sexe génétique quel que soit l'état génital de laNereis et la nature de l'intervention. La détermination des caractères sexuels somatiques des cirres parapodiaux apparaît donc comme étant très précoce (3 mois au moins avant la différenciation génitale) et stable.Par contre, les papilles pygidiales, caractère sexuel mâle dans les conditions normales, peuvent se différencier chez les très jeunes femelles dont l'épitoquie est déclenchée prématurément par décérébration et chez les femelles de tout âge dont les transformations hétéronéréidiennes sont réalisées en présence d'un milieu mâle (injection de produits génitaux, greffe sur un mâle). Les papilles pygidiales semblent donc déterminées précocement chez les deux sexes; leur différenciation est cependant inhibée chez les femelles au cours de la maturation génitale.

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Control of determination and the differentiation of the sexual somatic characters of Nereids (Annelida Polychaeta)

Summary The modalities of determination and differentiation of sexual dimorphism of Nereids (Annelida Polychaeta) were investigated inNereis pelagica L. andPerinereis cultrifera G. with experiments involving decerebration, castration (by X irradiation), grafts or injection of genital products.The sexual somatic characters of the parapodial cirri (swelling and crenellations) always develop according to the genetic sex, whatever the genital state of the Nereis and the nature of the intervention. Therefore the determination of the sexual somatic characters of the parapodial cirri appear to be determined in a very precocious and stable way (at least 3 months before the genital differentiation).The pygidial papillae, a male sexual character in normal conditions, can be formed by very young females in which heteronereidation is realized prematurely by decerebration, and by females of any age in which heteronereid transformations are realized in a male environment (e.g. by injection of genital products, or grafting onto a male). Therefore the pygidial papillae may be determined precociously in either sex; however their differentiation is normally inhibited in females in the course of genital maturation.

     

Genes specifically expressed in sexually differentiated female spheroids of Volvox carteri

Volvox carteri is a multicellular green alga with only two cell types, somatic cells and reproductive cells. Phylogenetic analysis suggests that this organism has evolved from a Chlamydomonas-like unicellular ancestor along with multicellularity, cellular differentiation, and a change in the mode of sexual reproduction from isogamy to oogamy. To examine the mechanism of sexual differentiation and the evolution of oogamy, we isolated 6 different cDNA sequences specifically expressed in sexually differentiated female spheroids. The genes for the cDNAs were designated SEF1 to SEF6. The time course of accumulation of each mRNA was shown to be distinct. The expression of some of these genes was not significantly affected when the sexual inducer was removed after the induction of sexual development. Sequence analysis indicates that SEF5 and SEF6 encode pherophorin-related proteins. Of these, SEF5 has the unique structural feature of a polyproline stretch in the C-terminal domain in addition to the one found in the central region.     

Dynamics and histological characteristics of gonadal sex differentiation in pejerrey (Odontesthes bonariensis) at feminizing and masculinizing temperatures

This study evaluated the effects of different temperatures on the histological process of sex differentiation in the pejerrey Odontesthes bonariensis, a fish with marked temperature-dependent sex determination (TSD), at feminizing, neutral, and masculinizing temperatures. Fish reared at three temperatures (17 degrees C, 24 degrees C, and 29 degrees C) from hatching were sampled weekly until 11 weeks and their gonads were examined by histology. The percentages of females at 17 degrees C, 24 degrees C, and 29 degrees C were 100%, 73%, and 0%, respectively. Sex differentiation occurred earlier and at a smaller body size at higher temperatures in both sexes. The first signs of ovarian differentiation were observed at 4 and 7 weeks at 24 degrees C and 17 degrees C, respectively, and those of testicular differentiation at 4 and 7 weeks at 29 degrees C and 24 degrees C, respectively. Body or gonadal growth rates before sex differentiation were not proportional to temperature and showed no sexual dimorphism at 24 degrees C, where both sexes were present. Thus, differential growth rate is probably not a factor in TSD or histological sex differentiation in pejerrey. Blood vessels were formed before sex differentiation in both sexes and at all temperatures, and may be important for sex differentiation. No signs of intersexuality were found in any of the groups, and this characterizes pejerrey as the differentiated type of gonochorist even at feminizing and masculinizing temperatures. Ovaries were formed by the same histological processes at feminizing (17 degrees C) and neutral (24 degrees C) temperatures and without any pathological features such as germ cell degeneration. The process of testicular formation was generally similar at 24 degrees C and 29 degrees C, but some fish at 29 degrees C had widespread germ cell degeneration before sex differentiation. This suggests that pathological processes leading to germ cell death, such as heat-induced dysfunction of the supporting somatic cells, could be involved in masculinization of the genetic females at high temperatures.     

Prenatal environmental influences on the production of sex-specific traits in mammals

The determination of offspring sex represents a delicate balancing act during which offspring must pass through several developmental levels in the presence of influential environmental factors. Successful expression of sex-specific traits requires genetic and hormone-based effects on several organizational and activational levels. Environmental factors can exert controls and disruptions at each of these levels. This review addresses the developmental stages at which environmental factors may influence the processes of sex determination, with an in depth focus on the prenatal stages, including the production of the primary and secondary sex ratios and the differentiation of functional secondary sexual characters.     

Gonadal sex differentiation in Alligator mississippiensis,a species with temperature-dependent sex determination

Temperature of egg incubation determines sex in Alligator mississippiensis hatchlings. To define the timing and morphology of sexual differentiation, alligator gonads were examined histologically and ultrastructurally throughout embryogenesis. At the male-producing temperature (33° C), the onset of testis differentiation occurred in most embryos during developmental stages 21–22, when a number of somatic cells in the medulla of the gonad became enlarged, forming presumptive Sertoli cells. Some enlarged somatic cells were also observed at the female-producing temperature (30° C) during gonadogenesis, but they were less widespread than at 33° C. Ovarian differentiation at 30° C began slighlty later, during stage 22–23, and was characterised by proliferation of germs cells in the cortex of the gonad. Testis formation in alligators may depend upon presumptive Sertoli cells differentiating prior to a critical event in embryogenesis, such as germ cell proliferation and meiosis. If follows that ovary formation occurs if this requirement is not met, as at lower incubation temperatures.     

Ontogeny of sexual dimorphism in the Long-tailed Manakin Chiroxiphia linearis: long maturation of display trait morphology

Males of dimorphic species often show ornaments that are thought to have evolved through female choice or/and male–male competition. The sexual differentiation of similar morphologies occurs during ontogeny, resulting in differential sex and age-specific selection. The Long-tailed Manakin is a dimorphic species with a highly skewed mating system, the males of which delay plumage maturation over 3 to 4 years. We describe ontogenetic changes in feather morphology in this species through sexual maturity. Males showed a significant increase in length of the central rectrices with age, hence their degree of sexual dimorphism increased from zero in 1-year-old males to 189.5% in adults. In contrast, male tail length decreased with age. Wing length did not vary significantly with age, but females had relatively longer wings than males. Wing loading was greater in females and decreased with age in males. In adults, rectrix length was positively correlated with testis volume, supporting the hypothesis that secondary sexual characters can signal the condition of primary sexual characters. Rectrix length showed positive allometry with body size in males less than 4 years old, whereas older males showed negative allometry and females showed isometry. Wing area and wing loading shifted from negative to positive allometry in males of 2 to 3 years of age. Changes in male morphology during ontogeny in the Long-tailed Manakin appeared to be associated with their specific display behaviours. Age-related changes in allometric growth of rectrices in the Long-tailed Manakin suggested that young males invest disproportionately more in the length of this trait relative to their body size. This investment could act as a signal of competitive ability to move status position in their orderly queue.     

Temperature sex-reversal in amphibians and reptiles

The sexual differentiation of gonads has been shown to be temperature-sensitive in many species of amphibians and reptiles. In two close species of salamanders, Pleurodeles poireti and P. waltl, both displaying a ZZ/ZW mechanism of genotypic sex determination (GSD), the rearing of larvae at high temperatures (30 degrees-32 degrees C) produces opposite effects: ZZ genotypic males of Pleurodeles poireti become phenotypic females whereas ZW genotypic females of P. waltl become phenotypic males. Sex-reversal of these individuals has been irrefutably demonstrated through genetic, cytogenetic, enzymatic and immunological studies. In many turtles, both sexes differentiate only within a critical range of temperature: above this range, all the individuals become phenotypic females, whereas below it, 100% become phenotypic males. The inverse occurs in some crocodiles and lizards. In many species of these three orders of reptiles, females are obtained at low and high temperatures, and males at intermediate ones. Preliminary studies in turtles (Emys orbicularis) indicate that within the critical range of temperature, sexual phenotype conforms with GSD, but that above and below this range, GSD is overriden. Temperature shifts during larval development in salamanders and during embryonic development in reptiles allowed the determination of thermosensitive stages for gonadal differentiation. Estrogens synthesized in the gonads at these stages appear to be involved in their sexual differentiation, higher levels being produced at feminizing temperatures than at masculinizing ones. The phenomenon of temperature sensitivity of gonadal differentiation occurs in species showing a very early stage in the evolution of sex chromosomes. Its adaptive value, chiefly in reptiles, remains an open question.     

Preliminary data on the influence of rearing temperature on the growth and reproductive status of fathead minnows Pimephales promelas

An investigation into the influence of temperature on the growth and reproductive status of the fathead minnow Pimephales promelas revealed that, while there was no clear effect of treatment on sex differentiation, ovarian tissue from female fish reared under the highest temperature regime contained large amounts of undefined tissue containing no germ cells. Furthermore, both male and female fish exhibited differences in length mass, condition and somatic indices, and in the expression of secondary sexual characteristics. The patterns observed are discussed in the context of climate change.     

Density-dependent growth and sexual maturity of silver hake in the north-west Atlantic

Stock abundance was the most important predictor of sexual maturation of age 2 and 3 silver hake in the north-west Atlantic between 1973–1990. Growth at ages 1 and 2 in the southern stock was significantly and negatively correlated with stock abundance (r²>0.56, P <0.01). Sexual maturity may be mediated through competition and growth during the first and second years of life. In the northern stock, growth and stock abundance was not significantly correlated ( P >0.05). Here, increased sexual maturity at ages 2 and 3 during 1973–1990 may have occurred without increased somatic growth, already near its maximum, due to the relatively cooler water temperatures of the Gulf of Maine. Logistic regression models indicated that maturation is dependent on age, stock density and an age-density interaction.