Examination of the ability of gonadal sex change in primary males of the diandric wrasses Halichoeres poecilopterus and Halichoeres tenuispinis: estrogen implantation experiments

Primary males that function as males throughout their lives are often found among protogynous fishes such as wrasses and parrotfishes. However, the issue of whether the sexuality of primary males involves gonochorism or hermaphroditism remains uncertain. To clarify this, we implanted estradiol-17beta (E2) into the body cavities of primary males of two protogynous wrasses, Halichoeres poecilopterus and Halichoeres tenuispinis. At 51-63 days after implantation, primary males with E2 treatment in both wrasses were observed to develop ovarian tissues. These results suggest that primary males of Halichoeres wrasses potentially have the ability to change sex and that estradiol-17beta is related to gonadal transitions in primary males.     

Early gonadal development and primary males in the protogynous epinepheline, Cephalopholis boenak

Early gonadal development of the protogynous epinepheline, Cephalopholis boenak, was examined histologically in 289 specimens with standard length (L_S) of 42–130 mm, collected from May 2000 to April 2002 in Hong Kong waters, to determine male developmental pathways and establish its sexual pattern. All juvenile gonads developed an ovarian lumen with primary‐growth stage oocytes and scattered spermatogenic tissue prior to sexual differentiation and first sexual maturation. From this bisexual phase containing both female and male tissues, some gonads differentiated as ovaries with further oocyte growth to cortical‐alveolus and vitellogenic stages, the rest differentiated as testes with the proliferation of spermatogenic tissue and the formation of a sperm sinus. All testes retained the lumen and primary‐growth stage oocytes, and sperm sinuses ran within the gonad wall. Unlike most protogynous species, among functional males it was impossible to distinguish those resulting from juveniles through sexual differentiation (i.e. primary male) from those resulting from functional females through sex change (i.e. secondary male) based solely on testicular morphology. A proportion‐spermatogenic‐tissue index (I_ST) was, therefore, developed and determined to be a reliable quantitative indicator for distinguishing differentiating, primary males before a sperm sinus was evident, from differentiating females during sexual differentiation. Since sexually transitional specimens with the concominant appearance of degenerating vitellogenic, or later, stage oocytes and spermatogenic tissue in the gonads were previously noted from Hong Kong, diandric, protogynous hermaphroditism is confirmed in C. boenak. For species, such as this and other epinephelines, in which all males have the same testicular morphology, a complete analysis of a wide range of body sizes from juveniles to adults is necessary for understanding male developmental pathways, and determining sexual pattern.     

Morphological ontogeny of the gonad of three plectropomid species through sex differentiation and transition

The gonadal ontogeny through sex differentiation and transition of three protogynous coral trout species, Plectropomus leopardus , P. maculatus and P. laevis was described, based on anatomical and germinal differences along the length of the reproductive tract. Gonads of immature and mature females, sex changing individuals (transitionals) and males were examined. Specific anatomical features that were compared between sexual phases included the presence and structure of sperm sinuses, gonadal musculature and germinal cell types. All three coral trout species first differentiated as an immature female. The sexual pattern of P. leopardus and P. maculatus was concluded to be diandric protogynous hermaphroditism (males were derived from the juvenile phase as well as through sex change of mature females). Plectropomus laevis was found to be monandric as males were only derived through sex change in mature females. Structural changes did not occur concomitantly with the germinal changes associated with sex change in these Plectropomus species, which is atypical for protogynous species described to date. Precursory sperm sinuses in the dorso-medial region of the gonad were present, although non-functional, in a proportion of immature and mature females of all three species. These proportions, however, varied between species depending on the sexual pattern. The structural and germinal changes observed were hypothesized as anatomical adaptations that aid in minimizing time spent in the (non-reproductive) sexual transition phase and maximizing flexibility in male development in the diandric species.     

Presence of primary and secondary males in a population of the protogynous Synbranchus marmoratus

Synbranchus marmoratus , the 'swamp eel', is a protogynous diandric fish. The primary and secondary males can be distinguished from each other easily by differences in gonadal morphology. Primary males have lobular, unrestricted testes with central efferent ducts. The secondary male has a 'lamellar' testis, efferent ducts are present in the ventral region (new formation), lateral supports and it is covered by the former ovarian capsule. The length of primary male varies from 13 to 88 cm while secondary males range from 56 to 91 cm. Transitional individuals vary between 45 and 60 cm in length. The swamp eel population studied is composed of 80% primary males and 20% secondary males. Although gonadosomatic indices are always higher in primary males, they increase in secondary ones as the newly acquired stage progresses. The lamellar organization of the gonad of secondary males, the absence of this kind of testis in individuals smaller than 56 cm, and the presence of hermaphroditic fish, is evidence for protogyny in this species.     

Molecular analysis in true hermaphroditism: demonstration of low-level hidden mosaicism for Y-derived sequences in 46,XX cases

True hermaphroditism (TH) is an unusual form of sex reversal, characterized by the development of testicular and ovarian tissue in the same subject. Approximately 60% of the patients have a 46,XX karyotype, 33% are mosaics with a second cell line containing a Y chromosome, while the remaining 7% are 46,XY. Molecular analyses have demonstrated that SRY is present in only 10% of TH with a 46,XX karyotype; therefore, in the remaining 90%, mutations at unknown X-linked or autosomal sex determining loci have been proposed as factors responsible for testicular development. True hermaphroditism presents considerable genetic heterogeneity with several molecular anomalies leading to the dual gonadal development as SRY point mutations or SRY hidden gonadal mosaicism. In order to identify genetic defects associated with subjects with the disease, we performed molecular analyses of the SRY gene in DNA from blood leukocytes and gonadal tissue in 12 true hermaphrodites with different karyotypes. Our results using PCR and FISH analyses reveal the presence of hidden mosaicism for SRY or other Y sequences in some patients with XX true hermaphroditism and confirms that mosaicism for SRY limited to the gonads is an alternative mechanism for testicular development in 46,XX true hermaphrodites.     

Sex differences in the energetic content of reproductive tissues in the Blackeye Goby,Rhinogobiops nicholsii

Differential energetic investment in reproduction between the sexes has been a driving a force of life history theory and sexual selection. However, reproductive costs between the sexes have often been based on morphology, such as gonad mass and gonadosomatic indices (GSI), and few have directly measured the energy content of gonadal tissues in relation to GSI. Using the blackeye goby, Rhinogobiops nicholsii, we measured the energetic content of whole gonadal tissues, specifically testes, ovaries and associated reproductive tissues using oxygen bomb calorimetry. The energy content per gram unit of gonadal tissues was generally predictive of GSI, indicating that GSI is a reasonable measure of energetic costs. Interestingly, although females had greater gonadal mass, GSI and energy content per gram than males, the sex difference in energy content per mass unit was only 13 %, suggesting that gross indices such as gonadal mass or GSI may overestimate energetic costs where instead the cost difference in a unit gram of gonadal tissues between the sexes is smaller than often predicted. This study also demonstrates that although the cost of ovaries is greater than testes, males’ investment in reproductive tissue can be considerable, which is consistent with the often inflated reproductive success for males in haremic mating systems.     

Investigation of the ZFY gene in XX true hermaphroditism and Swyer syndrome

Summary Four patients with 46,XX true hermaphroditism and one patient with 46,XY pure gonadal dysgenesis (Swyer syndrome) were analyzed with a Y chromosome-derived probe that detects a specific fragment on the short arm of the Y chromosome in the putative testicle-determining region and also a fragment on the short arm of the X chromosome. Normal males and females, an individual with Turner syndrome, and patients with various causes of anomalous gonadal differentiation accompanied by cytogenetically present Y chromosome were used as controls. The Y-specific fragment was not detected in any of the persons with 46,XX true hermaphroditism. However, this fragment was positive in the 46,XY female and in all Y-bearing patients. Cytogenetic and molecular absence of the ZFY sequence in 46,XX true hermaphrodites calls for explanations other than the classic embryogenie theory. The absence of testicular differentiation in the ZFY-positive XY female evidences functionally altered sex determination or, alternatively, defective gonadal receptors.     

Early gonadal differentiation in the Mexican snook Centropomus poeyi (Centropomidae,Perciformes, Teleostei) suggests protandric hermaphroditism

ABSTRACT

This study describes for the first time the early gonadal morphogenesis and raises the possibility of occurrence of protandric hermaphroditism in the Mexican snook (Centropomus poeyi). To achieve this, histological analysis of early gonadal differentiation was performed in 105 juvenile specimens ranging from 136 to 367 days post-hatching (dph). The early gonadal differentiation of the Mexican snook started at 178–213 dph and was completed at 355–367 dph. Active spermatogenesis was observed at 355–367 dph, once the compartmentalization of testis in germinal and interstitial compartments was accomplished. Our study demonstrates that in the Mexican snook, early gonadal differentiation is directed to produce 100% males, implying protandric hermaphroditism and showed the presence of a long-lasting period of gonadal differentiation, which makes this species highly sensitive to environmental cues.     

Patterns of gonad structure in hermaphroditic gobies (Teleostei Gobiidae)

Synopsis Hermaphroditism has been reported for a small number of gobiid fishes, but the extent of this sexual pattern within the family is not known. Gonad structure was examined in one or more species from twenty-one gobiid genera. No evidence of hermaphroditism was found in the species selected from 14 genera. Laboratory studies supported the conclusion of gonochorism for the examined species in four of them:Asterropteryx, Bathygobius, Gnatholepis, andPsilogobius. Currently, the absence of precursive testicular tissues associated with the ovary in females, in conjunction with no retained ovarian features in the testes of males, appear to be reliable indicators of a gonochoristic sexual pattern in gobiid fishes. Evidence for hermaphroditism was observed in seven genera:Eviota, Trimma, Fusigobius, Lophogobius, Priolepis, Gobiodon, andParagobiodon. Protogyny was experimentally confirmed inE. epiphanes, and the gonad structure in another nine of ten species ofEviota suggested either protogyny or protogynous tendencies. With the exception ofGobiodon andParagobiodon, which exhibited similar gonadal structure, ovarian and testicular structure varied considerably among the hermaphroditic genera examined, both with regard to the configuration and to the degree of development of ovarian and testicular tissues, or testicular tissue precursors. Findings of this study indicate that hermaphroditic gonad structure will prove to be a useful trait in determining evolutionary relationships within the Gobiidae.     

Effects of gonadal steroid hormones on hibernation in the Turkish hamster (Mesocricetus brandti)

Summary The Turkish hamster (Mesocricetus brandti) is a photoperiodic species in which exposure to a short day photoperiod induces gonadal atrophy. When hibernating male Turkish hamsters were administered testosterone via subcutaneous silastic capsules hibernation was abruptly terminated. The threshold serum testosterone level required to prevent hibernation was intermediate between the levels observed in males with fully-regressed and fully-functional testes. Dihydrotestosterone was as effective as testosterone in blocking hibernation. Estradiol had a partial inhibitory effect. Progesterone and corticosterone implants had no effect on hibernation. Similar results were obtained in female hamsters. The total period of hibernation for untreated males under laboratory conditions was usually 5–6 months. In most animals testicular growth began to occur toward the end of that period. As gonadal growth continued bouts of torpor decreased in frequency and duration, and hibernation was terminated when the testes approached reproductive size. Castrated males continued to hibernate much longer than intact animals. These observations suggest that in nature decreasing day length in the fall initiates gonadal regression which is followed by cold-induced hibernation. In the spring spontaneous recrudescence of the testes may lead to termination of the dormancy period. This mechanism may enable the species to prepare for the reproductive season with maximum efficiency.Supported by NIH Research Grant HD-10478 and by a grant from the Connecticut Research FoundationThe data in this paper were presented in part at the Annual Meeting of the American Society of Zoologists, Toronto, December 26–30, 1977     

Hypertrophy of gonadotropin releasing hormone-containing neurons after castration in the teleost, Haplochromis burtoni.

In the African cichlid fish, Haplochromis burtoni, males are either territorial or nonterritorial. Territorial males suppress reproductive function in the nonterritorial males, and have larger gonads and larger gonadotropin-releasing hormone- (GnRH) containing neurons in the preoptic area (POA). We describe an experiment designed to establish the causal relationship between large GnRH neurons and large testes in these males by determining the feedback effects of gonadal sex steroids on the GnRH neurons. Territorial males were either castrated or sham-operated, 4 weeks after which they were sacrificed. Circulating steroid levels were measured, and the GnRH-containing neurons were visualized by staining sagittal sections of the brains with an antibody to salmon GnRH. The soma areas of antibody-stained neurons were measured with a computer-aided imaging system. Completely castrated males had markedly reduced levels of circulating sex steroids [11-ketotestosterone (11KT) and testosterone (T)], as well as 17 beta-estradiol (E2). POA GnRH neurons in castrates showed a significant increase in mean soma size relative to the intact territorial males. Hence, in mature animals, gonadal steroids act as a brake on the growth of GnRH-containing neurons, and gonadal products are not responsible for the large GnRH neurons characteristic of territorial males.     

Sex determination: the amphibian models

We review and discuss current knowledge about sex determination in amphibians. The astonishing wide variety of mechanisms of genotypic sex determination is presented and discussed in an evolutionary context. We recall the natural occurrence of transitory juvenile hermaphroditism in some species. Our present knowledge of the mechanisms of sex determination in amphibians is compared to that in mammals. The influence of epigenetic factors, and especially temperature is highlighted. In amphibians, the influence of temperature on sexual differentiation, that can prevail over genotypic sex determination, remains poorly considered in publications. We suggest that studies on genetic and epigenetic factors of gonadal sex differentiation in amphibians could provide substantial information on the evolutionary process of sex determination mechanisms in current living vertebrates.     

Parental care and testosterone in males of the bank vole (Myodes glareolus): Sensitization and androgenic stimulation of paternal behavior

The relationship between parental responsiveness of bank vole males and their body weight, testes mass, and plasma and gonadal testosterone levels were examined. Two groups of voles were studied: Group I consisted of 14 breeding pairs where females gave birth to young within a month after formation of pairs, and Group II represented 13 pairs without offspring and signs of pregnancy in females. Males in Group I, unlike those in Group II, had contact with pups before the tests on parental responsiveness. In Group I, males were found to have larger testes and to exhibit a higher level of care-giving activity (pup retrieval) as compared to males in Group II. Both the plasma and gonadal testosterone levels in males exhibiting pup retrieval were revealed to be significantly higher than those for males exhibiting infanticide. Thus, promiscuity, competition for receptive females, and a higher level of testosterone secretion, which are characteristic of bank vole males during the breeding season, are not out of the realm of possibility of the males to care of young. Our findings suggest that factors promoting parental responsiveness in bank vole males are sensitization due to contact with pups and an increase in testosterone secretion. Obviously, there is a need to reexamine the role that testoster-one plays in regulating rodent paternal behavior.     

The gonadal anatomy and sexual pattern of the protandrous sex-reversing fish, Rhabdosargus sarba (Teleostei: Sparidae)

The gonadal anatomy and sexual pattern of Rhabdosargus sarba (Teleostei: Sparidae) was studied to provide some basic structural information for the subsequent investigations on the endocrinology of protandrous hermaphroditism in this fish. Evidence derived from relating sex to differences in body size, from gonadal histology and from biopsy, revealed the occurrence of natural sex reversal from male to female in this species. The gonad of R. sarba possessed topographically distinct male and female zones that were well separated by connective tissue. Based on gross-anatomical and histological observations, four types of gonad were distinguished and were designated as Types I-IV in the present study. Active spermatogenetic tissue was present in the Type I, II and IV gonads. Dormant oogonia and perinucleolar oocytes were found in the Type I (male) and II (intersex) gonads, respectively. In the Type III (female) gonad, a functional ovarian zone was observed and the testicular tissue was vestigial. The existence of ovarian tissue as an oogonial band in the Type IV (male) gonad, which was found more commonly in large specimens, suggested that these functional males might not undergo sex reversal in their life cycle. The interrelationship of the different types of gonad is discussed with reference to protandrous hermaphroditism.     

Maturation costs affect maturation timing: sexual reproduction in a heterogonic hydra

If maturation is more costly for females, they may need more distinct environmental cues to induce sexual reproduction than males. We verified this hypothesis by comparing the indirect costs of maturation to males and females of the heterogonic Hydra oligactis, reproducing both asexually and sexually. The laboratory experiments revealed that males mature 2 weeks earlier than the first females at falling temperatures simulating the natural conditions that precede sexual reproduction. The difference between the energy costs of maturation for males versus females has been considered a likely factor responsible for the observed difference in maturation time. Available food supply positively affected the percentage of sexually mature females, indicating that females are more sensitive to food limitation than males. The number of gonads was correlated positively with the size of mature hydra for both males and females. However, males produced twice as many testes as ovaries produced by females. We postulate that females are induced later than males in order to prevent gonadal development after an unseasonable drop in temperature. As sexual reproduction in H. oligactis interferes with asexual budding, under favorable conditions for asexual proliferation unnecessary gonadal development decreases an individual’s fitness through reduction of the number of produced offspring.     

Hypertrophy of gonadotropin releasing hormone-containing neurons after castration in the teleost,Haplochromis burtoni

In the African cichlid fish, Haplochromis burtoni, males are either territorial or nonterritorial. Territorial males suppress reproductive function in the nonterritorial males, and have larger gonads and larger gonadotropin-releasing hormone- (GnRH) containing neurons in the preoptic area (POA). We describe an experiment designed to establish the causal relationship between large GnRH neurons and large testes in these males by determining the feedback effects of gonadal sex steroids on the GnRH neurons. Territorial males were either castrated or sham-operated, 4 weeks after which they were sacrificed. Circulating steroid levels were measured, and the GnRH-containing neurons were visualized by staining sagittal sections of the brains with an antibody to salmon GnRH. The soma areas of antibody-stained neurons were measured with a computer-aided imaging system. Completely castrated males had markedly reduced levels of circulating sex steroids [11-ketotestosterone (11 KT) and testosterone (T)], as well as 17β-estradiol (E₂). POA GnRH neurons in castrates showed a significant increase in mean soma size relative to the intact territorial males. Hence, in mature animals, gonadal steroids act as a brake on the growth of GnRH-containing neurons, and gonadal products are not responsible for the large GnRH neurons characteristic of territorial males. © 1992 John Wiley & Sons, Inc.     

Mitinokuidrilus excavatus n. g., n. sp., a Marine Tubificid (Oligochaeta) with a Unique Mode of Reproduction

Mitinokuidrilus excavatus n. g., n. sp. is described from shallow subtidal coarse sands in northern Japan (NW Pacific). The species is characterized by a unique mode of sexual reproduction. Each of the two types of mature worms represents the opposite sex: "male" worms have testes, seminal vesicles, male ducts and small spermathecae; "female" individuals possess clitellum, ovaries, ovisac, female ducts and fully developed spermathecae. No mature worms with intermediate sexual condition were collected. The taxonomic position and the possibility of consecutive hermaphroditism of the present species are discussed.