The gonads of Aegla platensis Schmitt (Decapoda, Anomura, Aeglidae): a macroscopic and histological perspective

The aim of this study is to characterize the gonads of Aegla platensis, relating aspects of colour and size of ovaries, testes and vasa deferentia (VD) to histological observations. The ovaries are H‐shaped, extending from behind the stomach and ending at the 1st or 2nd abdominal somite. The male has a pair of testes from which the VD issue and extend over the pereon. For males and females, macroscopic categories of gonad development are defined. Stages of the male gonad are defined as types 1, 2 and 3. Type 1 includes the less developed gonads, and type 3 includes extremely developed testes and completely differentiated VD. The ovaries are classified into four stages according to their colour: I (white), II (yellow), III (orange) and IV (red), beginning with the least developed gonads. The number and size of oogonia and oocytes depend on the stage of the ovary and coincide with the different degrees of development as indicated by ovary colour. In males, the presence or absence of spermatozoa in the testes and VD is determined only for the more developed gonads. Neither spermathecae (female) nor spermatophores (male) were found. The lack of spermatophore in the present species is a rare characteristic among the anomurans.     

Sex determination and sexual differentiation in the avian model

The sex of birds is determined by the inheritance of sex chromosomes (ZZ male and ZW female). Genes carried on one or both of these sex chromosomes control sexual differentiation during embryonic life, producing testes in males (ZZ) and ovaries in females (ZW). This minireview summarizes our current understanding of avian sex determination and gonadal development. Most recently, it has been shown that sex is cell autonomous in birds. Evidence from gynandromorphic chickens (male on one side, female on the other) points to the likelihood that sex is determined directly in each cell of the body, independently of, or in addition to, hormonal signalling. Hence, sex-determining genes may operate not only in the gonads, to produce testes or ovaries, but also throughout cells of the body. In the chicken, as in other birds, the gonads develop into ovaries or testes during embryonic life, a process that must be triggered by sex-determining genes. This process involves the Z-linked DMRT1 gene. If DMRT1 gene activity is experimentally reduced, the gonads of male embryos (ZZ) are feminized, with ovarian-type structure, downregulation of male markers and activation of female markers. DMRT1 is currently the best candidate gene thought to regulate gonadal sex differentiation. However, if sex is cell autonomous, DMRT1 cannot be the master regulator, as its expression is confined to the urogenital system. Female development in the avian model appears to be shared with mammals; both the FOXL2 and RSPO1/WNT4 pathways are implicated in ovarian differentiation.     

Gonadal development and non-functional protogyny in a coral-reef damselfish, Dascyllus albisella Gill

All gonads of the Hawaiian dascyllus Dascyllus albisella , irrespective of the final sex of individuals, developed an ovarian lumen and primary-growth-stage oocytes after an initially undifferentiated state. From this ovarian state or from more differentiated ovaries, some gonads redifferentiated into testes. None of 117 individuals examined had a gonad containing degenerating vitellogenic oocytes and proliferating spermatogenic tissue. Eleven individuals had gonads containing degenerating cortical-alveolus-stage oocytes and developing spermatogenic tissue. The size of these individuals overlapped with the female size range in which the majority of the females were still in the middle of the maturation process. They were absent from the larger size range where the majority of females had vitellogenic oocytes. This indicated that the transition toward maleness is likely to have occurred after the onset of cortical-alveolus stage, but before final oocyte maturation and spawning as females. Therefore the protogynous pattern of gonadal development was non-functional. There was no dimorphism in the sperm duct configuration, and all the testes were secondary testes reported for diandric, protogynous species with undelimited gonads. Very early development of an ovarian lumen appeared to have resulted in a secondary-male configuration in all testes, although redifferentiation into males appeared to have occurred before sexual maturity and spawning as females.     

Morphological and histological features of the gonad structure in hermaphroditic walleye pollock <Emphasis Type="Italic">Theragra chalcogramma</Emphasis> (Gadidae)

Morphology of hermaphroditic gonads is studied in the individuals of walleye pollock Theragra chalcogramma collected in different regions of the seas of the North Pacific from 1987 to 2014. Based on the external morphological characteristics of sexual glands of 17 fishes, the most frequent types of the structure of bisexual gonads are described. Histological analysis shows the absence of differences in the composition and condition of oocytes in the left and right-paired ovaries, and the testes and ovaries of each individual are at the same maturity stage. In the ovigerous lamellae of ovaries in the areas adjacent to testes the zones of oocyte resorption are observed. These zones are located exclusively near the joining of the female and male parts of the gonads. The development of ovaries and testes of bisexual gonads is similar to that in the majority of normally maturing males and females collected during the same period. The occurrence of hermaphrodites is 0.0003–0.0016% from the total number of investigated exemplars.     

Gonadal development in T16H/XSxr hermaphrodite mice

Sexual development was studied in 25 hermaphrodite mice with the genotype T16H/XSxr. The majority of the animals had a male phenotype similar to that seen in XXSxr males. A few, however, had feminized external genitalia and were classified as females. Examination of the gonads and reproductive tracts of the male hermaphrodites revealed a strong tendency for the left gonad to be more masculine than the right. Most of the gonads in male and female hermaphrodites appeared to be ovaries or testes rather than ovotestes.     

Juvenile bisexuality in the red sea bream,Pagrus major

The histology of the gonad of the red sea bream,Pagrus major, was examined in order to study the early gonadal development, sexual maturation and sex ratio in a natural population. A total of 1,117 fish between the ages of 4 months and 8 years were examined. Gonads of 4-month-old fish were either sexually undifferentiated with a central cavity, or ovarian in form. Gonads of 12- and 18-month-old fish were ovaries or bisexual gonads, while those of 2-year-old fish were ovaries, bisexual gonads or testes. Fish aged between 3 and 8 years had ovaries or testes, except for a few bisexual gonads found in 3- and 4-year-old fish. The chronological appearance of females, hermaphrodites and males in that order, and histological evidence, suggested that the testis originates from the ovary via a bisexual gonad in the juvenile stage. The sex ratio of females to males at the age of 2 years and over was about 1:1, suggesting that hermaphroditic red sea bream appear in about 50% of the juvenile population. The sexual pattern in this species, therefore, is concluded to be gonochorism with a bisexual juvenile stage.     

The development of carp gonads in warm water aquaria

The development of carp gonads in warm water (23°C) aquaria under controlled conditions is described. In this environment males mature at 6 months of age. Females ripen at 14 months, and by 15 months 25% of these have started to spawn, whereas under natural conditions female European carp do not ripen until they are 4 years old. Fishes do not lay all their eggs at once, as evinced by the finding of partly-spent ovaries. Sexual maturation of the ovaries has been described in six stages, based on histological changes, and associated with changes in the female gonado-somatic index and the maximum ova diameter. The maturation of testes occurs in four stages. The percentage incidence of each stage of ovarian maturation has been calculated for the 6th to the 15th month. Larger fishes become sexually mature before smaller fishes.     

Observations on mass atresia and skipped spawning in northern Atlantic cod, from Smith Sound, Newfoundland

Atlantic cod Gadus morhua were collected from Smith Sound, Newfoundland in January 1999. Visual examination of females (n=150) and males (n=126) revealed that some large fish (42–79 cm) had underdeveloped gonads. Histological examination of underdeveloped ovaries indicated that the majority of these females were undergoing mass resorption of oocytes and would not have spawned in 1999. Fish in this condition included females that were aborting their first attempt at maturation and females that had spawned the previous year but were failing to re-ripen. Somatic and liver condition were significantly lower (P<0·05) for fish undergoing mass oocyte resorption than ripening females, suggesting that the interruption in the maturation cycle may have been related to insufficient nutrient storage. In males, testes of some adult fish were considered to be non-reproductive as they showed no signs of ripening and probably would not have spawned in 1999. Liver condition was significantly higher (P<0·05) for non-reproductive males than those that were ripening. Disruptions in male and female reproductive cycles may also have been related to water temperatures that were too cold (0–0·5° C) for successful gamete development. Immature gametes (perinucleolar oocytes in females; spermatogonia in males) showed no signs of breakdown in non-reproductive individuals, suggesting that they retained the potential to develop and spawn gametes in 2000.     

Characteristics of gonads and oviducts in hatchlings and young of Chelydra serpentina resulting from three incubation temperatures

Eggs of Chelydra serpentina were incubated at 30°C and 26°C. In addition, incubation was done at 20°C during the temperature-sensitive period for sex determination. Incubation at 20°C and 30°C resulted in females; incubation at 26°C resulted in males in 99% of the cases. The average gonadal length was less in the males. The average length of the 20°C ovaries did not vary significantly from that of the 30°C ovaries. The condition of the oviducts was correlated with histology of the gonads in hatchlings and in 3-month-old animals. When at least one of the oviducts was obvious and intact, ovaries were present. If the oviducts were absent or interrupted, testes were present. Histological characteristics of the gonads resulting from the three incubation temperatures are described. In the 26°C testes, cellular infiltrations occurred frequently. The ovaries of 20°C hatchlings tended to have a less developed germinal epithelium than that of the 30°C animals. Also, epithelial cysts occurred frequently in the 20°C ovaries. The incidence of follicles at 3 months was not differential.     

Gonadal Growth in Embryos of Sex reversed Mice

Gonadal volumes were measured in litters of mouse embryos, aged 15 and 16 days, which were segregating for the Sex reversed factor. The testes of XY embryos were much larger than the ovaries of female embryos and the testes of XX Sex reversed males were almost, but not quite, as large as those of XY males. One of the 13 Sex reversed embryos had ovotestes.
It is concluded that the Sex reversed factor causes an increase in the growth rate of XX gonadal rudiments and that this is a necessary prerequisite for testicular differentiation. It is further postulated that the failure of spermatogenesis seen in adult Sex reversed , XX males is a result of the suboptimal growth rate of the gonads, compared to that of normal testes seen in the embryos. The formation of ovotestes may result from a growth rate which is at a lower limit of that necessary for testicular differentiation.     

Steroid metabolism in gonads of turtle embryos as a function of the incubation temperature of eggs

In embryos of many reptiles, the sexual differentiation of gonads is temperature-dependent. In the turtle Emys orbicularis, all individuals become phenotypic males at 25 degrees C, whereas 100% phenotypic females are obtained at 30 degrees C. Steroid metabolism in embryonic gonads was studied at both temperatures, during and after the thermosensitive period for sexual differentiation. Pools of gonads were incubated for various times, with 3 beta-hydroxy-5-pregnen-20-one (pregnenolone), progesterone, dehydroepiandrosterone or 4-androstene-3,17- dione as substrates. The analysis of metabolites combined two successive chromatographies (HPLC and TLC) and autoradiography. Conversion of pregnenolone to progesterone and of dehydroepiandrosterone to 4-androstene-3,17-dione was more important in testes at 25 degrees C than in ovaries at 30 degrees C. In ovaries, a large amount of 5-pregnene- 3 beta,20 beta-diol was formed from pregnenolone, and 5-androstene-3 beta,17 beta-diol was produced from dehydroepiandrosterone. In both testes and ovaries, 5 alpha-pregnane and 5 alpha-androstane derivatives were the main metabolites obtained from progesterone and 4-androstene-3,17-dione, respectively. Progesterone was also converted to 20 beta-hydroxy-4-pregnen-3-one. Dehydroepiandrosterone and 4-androstene-3,17-dione were also metabolized into 11 beta-hydroxy-4-androstene-3,17-dione (only in testes), testosterone, 11 beta,17 beta-dihydroxy-4-androstene-3-one, 17 beta-hydroxy-4-androstene-3,11-dione (low amounts in testes, traces in ovaries), 17 alpha-hydroxy-4-androstene-3-one, estrone and estradiol-17 beta (traces).     

Reproductive biology of Astyanax fasciatus (Pisces: Characiformes) in a reservoir in southeastern Brazil

To study the reproductive biology of Astyanax fasciatus (Cuvier, 1819) in Furnas Reservoir, Minas Gerais, Brazil, a total of 1307 specimens were captured in bimonthly sampling from August 1993 to July 1994. The sex ratio showed a predominance of females, representing 65.2% of the total sample. The stages of gonadal maturation and spawning type were determined through macro- and microscopic analysis of the gonads as well as by variation in the gonadosomatic indices. A . fasciatus showed fractionated spawning and reproduction throughout the year, with spawning peaks influenced by water temperature and rainfall. Males and females initiated gonadal maturation at a mean standard length of 6.4 and 6.5 cm, respectively. During gonadal maturation, females showed a reduction in hepatosomatic index (from 1.06 to 0.83), suggesting that hepatic substances are transferred from the liver to the ovaries. In the reproductive period, A. fasciatus had lower stomach repletion and coelomic fat indices, indicating that this species ate less and consumed more fat reserves when reproduction had the maximum GSI (11.3 for females and 2.7 for males). Weight of the ovaries had a positive influence on the condition factor (K1), as the lowest K2 value (weight without gonads) were obtained during maturation, confirming the influence of the ovaries upon the physiological condition of the females. In weight–length relationship, parameter b was 3.02 for females and 2.23 for males, and the correlation coefficient ( r ²) was 0.84 and 0.66, respectively.     

Histological study of the development and sex differentiation of the gonad in the European eel

The histological structure of the gonads was studied in yellow eels sampled from a coastal lagoon and from stocks reared in an aquaculture plant showing different sex ratios. Gonad development related to body size rather than to age and underwent an intermediate stage characterized by a structure of an early testis but containing oogonia and oocytes. This gonad was called the Syrski organ and the stage juvenile ambisexual. Ovaries were found in eels from 22–30 cm in length, possibly derived from undifferentiated gonads or from Syrski organs. Fully differentiated testes were found in eels >35 cm, derived from Syrski organs. These observations support the results of previous research. From elvers and in eels up to 15–16 cm in length, growth of the gonadal primordium is due to primordial germ cell migration. In eels > 15 cm multiplication of primordial cells begins. Oogonial clones were found in eels > 18 cm in length, whilespermatogonium B clones were observed in eels >30 cm in length. The dynamics of sex differentiation was different among stocks with different ultimate sex ratios: ovaries were found in shorter eels in stocks with a prevalence of females, in longer eels in stocks with a prevalence of males. This result supports the hypothesis of a metagametic (environmental) sex determination. The somatic cells in contact with germ cells and those in the interstitium appeared early during gonad development and preceded germ cell differentiation. This suggests that somatic cells are the targets of the environmental factors influencing sex differentiation.     

Ligula intestinalis infection as a potential source of bias in the bioindication of endocrine disruption in the European chub Leuciscus cephalus

European chub Leuciscus cephalus collected from five localities in the lowland and subalpine regions of Austria were analysed for oestrogenic effects of endocrine-disrupting chemicals and the presence of the plerocercoid of the tapeworm Ligula intestinalis. Of 1494 chub analysed, only seven (six males, one female) were found to be infected with single, but large plerocercoids up to 15 cm in length. Ligula-infected fish showed comparatively immature gonads, as demonstrated by the gonadosomatic index and gamete developmental stages. Plasma levels of the egg precursor protein vitellogenin also showed concentrations ranging below the detection limit. The present results indicate that chub infected with L. intestinalis and exposed to exogenous oestrogenic compounds can result in reduced gonadal maturation and produce false oestrogen-positive diagnoses in male fish. For plasma vitellogenin levels, L. intestinalis infections can result in false oestrogen-negative diagnoses in male and female fish.     

Gonadal development and diandric protogyny in two populations of Dascyllus reticulatus from Madang, Papua New Guinea

Two Dascyllus reticulatus populations from Madang, Papua New Guinea exhibited diandric protogyny. In both populations, gonads began as undifferentiated, and then developed oocytes in the primary growth stage and an ovarian lumen. From this ovarian state or from more developed ovaries containing oocytes beyond the primary‐growth stage, some gonads developed into testes. The first sign of testicular development was degeneration of oocytes, degeneration of oocytes in the primary growth stage in ovarian gonads and degeneration of oocytes of all growth stages present including the primary growth stage in ovaries, which was then followed by development of spermatogenic tissue. In both populations, most of the fish that had gonads with degenerating oocytes were smaller than the smallest mature females, indicating that development towards testes was mostly initiated in immature gonads containing only pre‐vitellogenic oocytes. On some occasions, however, females as large as other mature females also had gonads with degenerating oocytes, suggesting that development towards testes may have occurred in mature ovaries as well. This latter notion is further strengthened by the discovery of a fish having a gonad that contained both degenerating vitellogenic oocytes and developing spermatogenic tissue. Taken together, these results suggest that D. reticulatus can exhibit diandric protogyny, because testes in D. reticulatus developed from juvenile gonads as well as from mature ovaries.     

The state of gonads of resident sockeye salmon <Emphasis Type="Italic">Oncorhynchus nerka</Emphasis> from the Tolmachev Reservoir

Morphology of gonads and structure of sex cells in females and males of the resident sockeye salmon Oncorhynchus nerka—kokanee—from Tolmachevskoe Reservoir are investigated. Anomalies in structure of sex cells and structure of oocytes are found. Partial or mass resorpbion of cells in the ovaries of males and testes of males is found, leading to sterility of gonads. The relationship between anomalies found in structure of the sex system of kokanee, changes in biological parameters of fish and the increase of the population abundance is discussed.     

Testes of XX ↔ XY chimeric mice develop from fetal ovotestes

The majority of XX ? XY chimeric mice develop into fertile males. The sexual differentiation of the gonads in these animals has been examined on days 12–14 postcoitum to determine if their development parallels that of normal testes. It was found that 50% of chimeric fetuses, the proportion predicted to be XX ? XY, had neither normal testes nor ovaries. Instead, ovotestes were present, with varying proportions of presumptive ovarian and testicular tissue. On day 12 the ovotestes were organized with testicular tissue in the central region and ovarian tissue at the craniad and/or caudad poles. In the more advanced fetuses there was evidence of regression of the ovarian portion, which would account for the testes found in adults. These results are discussed in light of current theories of sex determination and differentiation and what was previously known about gonads of sex mosaics.     

Testes of XX in equilibrium with XY chimeric mice develop from fetal ovotestes

The majority of XX in equilibrium with XY chimeric mice develop into fertile males. The sexual differentiation of the gonads in these animals has been examined on days 12-14 postocoitum to determine if their development parallels that of normal testes. It was found that 50% of chimeric fetuses, the proportion predicted to be XX in equilibrium with XY, had neither normal testes nor ovaries. Instead, ovotestes were present, with varying proportions of presumptive ovarian and testicular tissue. On day 12 the ovotestes were organized with testicular tissue in the central region and ovarian tissue at the craniad and/or caudad poles. In the more advanced fetuses there was evidence of regression of the ovarian portion, which would account for the testes found in adults. These results are discussed in light of current theories of sex determination and differentiation and what was previously known about gonads of sex mosaics.