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.     

Gonadal development and an indication of functional protogyny in the Indian damselfish (Dascyllus carneus)

The objective of this study was to determine the sexual pattern of the Indian dascyllus Dascyllus carneus . After an initially undifferentiated state, gonads of D. carneus developed an ovarian lumen and primary growth stage oocytes, and subsequently cortical-alveolus stage oocytes. From ovaries with cortical-alveolus stage oocytes and from more developed ovaries, some gonads redifferentiated into testes. From a sample of 163 individuals, two had a gonad containing degenerating vitellogenic oocytes and proliferating spermatogenic tissue, nine had a gonad containing degenerating cortical-alveolus stage oocytes and spermatogenic tissue, and five had a gonad with degenerating primary growth stage oocytes and spermatogenic tissue. The size of these individuals overlapped greatly with the size range of mature females, suggesting that at least in some individuals, redifferentiation toward a testis occurred after spawning as females. This indicates that D. carneus is a functional, diandric protogynous hermaphrodite. Removal of a dominant male(s) did not induce a sex change in any of the ranking females in the laboratory and field groups. There was no difference in the number of chases and signal jumps performed by the ranking female between control and experimental field groups, or before and after removal of the male. However, the sizes of the ranking females were at or beyond the size range of individuals with a mixed-stage gonad, suggesting that the developmental window for female-to-male sex change may not be open ended. In 41 of 43 field groups, in which sex of fish was determined histologically or by the shape of the urogenital papilla, one to several highest size ranks were occupied by males, followed by one to several females. Mature males, however, were not limited to the highest ranks and occurred at various lower size ranks within groups. Individuals with a mixed-stage gonad also occupied various size ranks within groups.     

Gonad development and evidence of protogyny in the red-throat emperor on the Great Barrier Reef

The gonad development in the red-throat emperor Lethrinus miniatus is described and the first detailed evidence for protogyny in this species provided. The identification of transitional individuals, bimodal sex-specific size-frequency distributions and female biased sex ratios suggest that L. miniatus is most likely a protogynous hermaphrodite. Transitional L. miniatus gonads were characterized by the concurrent degeneration of all oocytes and the proliferation of spermatocysts near the edge of the lamellae, an increase in blood vessels along strands of stromal tissue within the lamellae and the formation of multiple sperm sinuses. The sites of oocyte degeneration and proliferation of spermatocysts were spatially segregated. An increase in blood vessels along strands of stromal tissue within the lamellae of transitional phase gonads is likely to assist in the breakdown of oocytes and the proliferation of spermatocysts. Most mature resting females containing spermatocysts occurred within the transitional size-frequency distribution, suggesting that the presence of spermatocysts in these females may be an early sign of sex change. Oocytes within female gonads were interrupted by filamentous strands of stromal tissue within the lamellae. The testis contained a remanent ovarian lumen but no residual oocytes. Three characteristics of transitional L. miniatus gonads were found to be unusual and described for few other species of coral reef fishes. These included the absence of oocytes within testes, increased numbers of blood vessels, and the presence of strands of stromal tissue within the lamellae.     

棉铃虫温度依赖的生长发育及雌性先熟现象

在昆虫中,雄虫先于雌虫羽化,称为雄虫先熟现象,而雌虫先于雄虫羽化,称为雌虫先熟现象。前者最为普遍,后者报道较少。本试验在20、22和25℃下对棉铃虫Helicoverpa armigera（Hilbner）的生长发育进行了详细的研究。结果显示发育历期随温度的升高而缩短,雌雄间发育历期有着显著的差异,各个温度下雌虫均比雄虫先羽化,表明棉铃虫属于雌性先熟种类,而这种差异主要是由于雌虫的蛹期较短所致。幼虫发育历期与蛹重呈显著的正相关性。     

Isolation and characterization of 16 microsatellite loci in the humbug damselfish, Dascyllus aruanus (family Pomacentridae)

Here we report on 16 microsatellite loci designed for the damselfish Dascyllus aruanus. All loci were tested on 98 individuals and were polymorphic (seven to 35 alleles). Expected heterozygosity ranged from 0.705 to 0.942. Six loci showed Hardy-Weinberg disequilibrium due to the occurrence of null alleles. Cross-species amplifications conducted within the genus Dascyllus (D. carneus, D. strasburgi, D. trimaculatus) lead to polymorphic fragments in 32 out of 48 tests. These 16 loci will enable future research into the behavioural ecology and population ecology of Dascyllus aruanus throughout the Indo-Pacific.     

Gonadal development and sex steroids in a female Arctic charr broodstock

Gonadal development and plasma levels of sex steroids were investigated in female Arctic charr at 3-week intervals over a 12-month period. Circulating levels of oestradiol-17β (E₂), testosterone (T) and 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) were measured by radioimmunoassay, and gonadal status assessed through histological examination and measurement of gonadosomatic index (GSI) and frequency distribution of oocyte size-classes. Gonadal recrudescence during March-July was characterized by modest but insignificant increases in plasma levels of E₂ (2–4 ng ml^?1) and T (2–5 ng ml^?1) and recruitment of oocytes into yolk accumulation. Only a small and insignificant rise in GSI and no apparent increase in oocyte diameter occurred during this period, indicating that the rate of yolk formation and oocyte growth was low. Following transformation from stage V (peripheral yolk granule stage) to stage VI (yolk granule migration stage) in late July, the vitellogenic oocytes entered a phase of rapid growth which resulted in a marked rise in GSI until ovulation commenced in late September. Gonadal growth during this period was accompanied by increases in plasma levels of E₂ and T which peaked at 11 ± 1 (mid-August) and 71 ± 5ng ml^?1 (late September), respectively. The levels of both steroids dropped rapidly during final maturation and ovulation, followed by a surge in plasma levels of 17,20β-P which peaked at an average of 74 ± 17 ng ml^?1 in early October. All three steroids returned to basal levels within a month after ovulation, and all steroids, except E₂, remained low until March of the following year. A slight increase in E₂ detected in February and March during the second season may have been associated with recruitment into vitellogenesis of a new generation of oocytes. It is suggested that the abrupt increase in vitellogenesis in late July may reflect a condition-dependent decision to proceed with maturation, once the energy reserves have been repleted during spring-early summer.     

Gonadal development and sex differentiation in the cichlid fish Cichlasoma dimerus (Teleostei, Perciformes): a light- and electron-microscopic study

Although the overall pattern and timing of gonadal sex differentiation have been established in a considerable number of teleosts, the ultrastructure of early stages of gonadal development is not well documented. In this study, gonads from larval and juvenile stages of laboratory-reared Cichlasoma dimerus were examined at the light-microscopic and ultrastructural levels. This freshwater species adapts easily to captivity and spawns with high frequency during 8 months of the year, providing an appropriate model for developmental studies. Larvae and juveniles were kept at a water temperature of 26.5 +/- 1 degrees C and a 12:12 hour photoperiod. Gonadal development was documented from 14-100 days postfertilization, covering the period of histologically discernible sex differentiation. Gonadal tissue was processed according to standard techniques for light and electron microscopy. C. dimerus, a perciform teleost, is classified as a differentiated gonochorist, in which an indifferent gonad develops directly into a testis or ovary. On day 14, the gonadal primordium consists of a few germ cells surrounded by enveloping somatic cells. Ovarian differentiation precedes testicular differentiation, as usual in teleost fishes. The earliest signs of differentiation, detected from day 42 onward, include the onset of meiotic activity in newly formed oocytes, which is soon accompanied by increased oogonial mitotic proliferation and the somatic reorganization of the presumptive ovary. The ovarian cavity is completely formed by day 65. Numerous follicles containing perinucleolar oocytes are observed by day 100. In contrast, signs of morphological differentiation in the presumptive testis are not observed until day 72. By day 100, the unrestricted lobular organization of the testis is evident. The latest stage of spermatogenesis observed by this time of testicular development is spermatocyte II.     

Reproductive cycle and sex inversion in razor fish, a protogynous labrid in the southern Mediterranean Sea

The reproductive biology of the Mediterranean razor fish Xyrichthys novacula was investigated by demographic data and histological analysis of the female, intersexual and male gonads. Specimens were collected by bottom trawl on a monthly basis between June 2000 and July 2001 in a sandy bay in southern Thyrrenian. Gonad histology confirmed that the Mediterranean razor fish is a monandric, protogynous hermaphrodite. Females reached first sexual maturity at 100 mm ( L _T) and the estimated mean L _T at first maturity ( L ₅₀) was 125 mm. Females exhibited asynchronous ovarian development and multiple ovulations occurred over the spawning period. Vitellogenesis started in early May and spawning occurred from late May until late September. Sexual transition involved a large‐scale atresia of all oocyte stages and a massive degeneration of ovarian tissue followed by primordial germ cells proliferation. Sex change began at spawning time (June) but transitional individuals tended to cluster at the end of the reproductive period (September). They accounted for 17·1% of the population sampled and were found in a broad size range (105–150 mm L _T).     

Male sterility, protogyny, and pollen-pistil interference in Plantago maritima (Plantaginaceae), a wind-pollinated, self-incompatible perennial

Evolution and maintenance of male sterility in seed plants can be explained by the maternal inheritance of mitochondria, which encode the trait, and by adaptive functions that enhance female fecundity in male-sterile compared to hermaphrodite individuals. Protogyny and male sterility can independently decrease the negative effect of pollen-pistil interference in self-incompatible species. In Plantago maritima, which possesses both traits, protogyny increases seed set in hermaphrodite individuals. This is shown both by a significantly positive association between seed set and retarded dehiscence of the anthers and by a more than 50% reduction in seed set following self-pollination. Male sterility does not seem to increase seed set further, as female and hermaphrodite plants do not differ significantly in mean seed set per capsule. Bagging experiments demonstrate strong self-incompatibility in the study populations. Hence, in P. maritima male sterility seems neither to prevent selfing nor to reduce the effect of pollen-pistil interference. Females had significantly larger stigmas than hermaphrodites, but seed set varied negatively with stigma length among females, indicating that the evolution of unisexuality in P. maritima is not due to prefertilization sex allocation. I therefore conclude that the genetical system of nucleocytoplasmic determination of gender is the main cause for maintenance of male sterility in P. maritima.     

Gonadal morphogenesis and sex differentiation in the viviparous fish Chapalichthys encaustus (Teleostei, Cyprinodontiformes, Goodeidae)

This study describes the structural and ultrastructural characteristics of gonadal sex differentiation and expression of Vasa, a germline marker, in different developmental stages of embryos and newborn fry of the barred splitfin Chapalichthys encaustus, a viviparous freshwater teleost endemic to Mexico. In stage 2 embryos, the gonadal crest was established; gonadal primordia were located on the coelomic epithelium, formed by scarce germ and somatic cells. At stage 3, the undifferentiated gonad appeared suspended from the mesentery of the developing swimbladder and contained a larger number of germ and somatic cells. At stages 4 and 5, the gonads had groups of meiotic and non-meiotic germ cells surrounded by somatic cells; meiosis was evident from the presence of synaptonemal complexes. These stages constituted a transition towards differentiation. At stage 6 and at birth, the gonad was morphologically differentiated into an ovary or a testis. Ovarian differentiation was revealed by the presence of follicles containing meiotic oocytes, and testicular differentiation by the development of testicular lobules containing spermatogonia in mitotic arrest, surrounded by Sertoli cells. Nuage, electron-dense material associated with mitochondria, was observed in germ cells at all gonadal stages. The Vasa protein was detected in all of the previously described stages within the germ-cell cytoplasm. This is the first report on morphological characteristics and expression of the Vasa gene during sexual differentiation in viviparous species of the Goodeidae family. Chapalichthys encaustus may serve as a model to study processes of sexual differentiation in viviparous fishes and teleosts.     

Gonadal sex differentiation and expression of Sox9a2, Dmrt1, and Foxl2 in Oryzias luzonensis

Oryzias luzonensis is closely related to the medaka, O. latipes. The sex of both species is determined by an XX‐XY system. However, the testis determining gene (DMY/Dmrt1bY) found in O. latipes does not exist in O. luzonensis. Instead, a different gene is thought to act as a testis determining gene. In this study, we focused the gonadal sex differentiation process in O. luzonensis under different testis determining gene. First, we observed the gonadal development of O. luzonensis histologically. We then analyzed the expression of Sox9a2/Sox9b, Dmrt1, and Foxl2 during early development. Our results suggest that the sexual differentiation of germ cells in O. luzonensis is initiated later than in O. latipes. However, the timing of the sexual differentiation of the supporting cell linage is similar between the species. genesis 47:289–299, 2009. © 2009 Wiley‐Liss, Inc.     

Gonadal maturation,fecundity, spawning,and timing of reproduction in the mud snail,Cerithidea cingulata,a pest in milkfish ponds in the Philippines

Summary

Gonadal maturation, spawning, fecundity and timing of reproduction of the snail Cerithidea cingulata in a brackish water pond in Molo, Iloilo, Philippines, are described. Snails 4–41 mm in shell length were sampled monthly from May 1997 to May 1998; 25% were <25 mm, 67% were 20–30 mm, and 8% were >30 mm. The sexes are separate and could first be distinguished at 15 mm. Males are aphallic, have narrower shells than females of the same length, and have bright yellow-orange testes overlying the digestive gland deep inside the shell. Females have more robust shells, an ovipositor at the right side of the foot, and yellow-green ovaries overlying the digestive gland. The sex ratio was one male to two females in the pond population studied. Gonadal maturation was monitored by means of gonadosomatic index (GSI, gonad weight as a percent of visceral weight); maturation stages were based on the gonad appearance (immature, developing, mature) and histology (immature, developing, mature, redeveloping). GSI increased with snail size, and reached 16% in a 33-mm female. The smallest mature males and females were 18–19 mm, and most snails >20 mm were mature, spawning, or redeveloping. Histological sections showed all stages of gametogenesis in mature male snails. The oocyte size-frequency distributions in mature females showed mostly mature oocytes and secondary oocytes, but also oogonia and primary oocytes. GSI and the frequency of snails at different maturation stages varied over the year. Both GSI and the frequency of mature snails were highest during the summer months, April to August. Nevertheless, mature snails occurred throughout the whole year, as did mating and egg-laying. Fecundity (= number of oocytes >70 pμ) increased with size in mature females 2041 mm; an average 25-mm female produced about 1,500 oocytes and larger females produced a maximum of about 2,500 oocytes. Eggs strings laid on the pond bottom were 45–75 mm long; an average 64-mm string contained 2,000 eggs 210+20 pm in diameter. The density of eggs strings was highest (80–120/m²) during March-September. Eggs hatched after 6–7 d into planktonic veligers, which in turn settle on the pond bottom 11–12 d later as juveniles. Juveniles 2–6-mm long were most abundant in the pond during August-October.     

Observation and establishment of gonad development stages in polyplacophorans (Mollusca): Chiton (Chiton) articulatus a case study

Gonad development stages (GDS) and, subsequently, the reproductive cycle are described by performing histology of some gonad portions. In polyplacophorans, gametogenesis is not enough to define GDS; further anatomical gonad features are relevant. In most adult polyplacophorans, the gonad is a simple anatomical structure that resembles and operates as one single gonadal acinus without glandular structure. These features have gone unnoticed causing inaccurate GDS assignment and, consequently, imprecise reproductive season in polyplacophorans. Here, dissection protocols that allow extracting a compact gonad are established. Emphasizing the anatomical structure of the whole gonad and the displacement of gametes, five GDS were assigned to both sexes of Chiton (Chiton) articulatus: I‐goniogenesis, II‐development, III‐ripe, IV‐spawning, V‐rest. Tissue platelets contribute importantly to GDS assignment and even help distinguishing between males and females. Neither a randomly selected portion of gonad nor a longitudinal section are recommended because it leads to misinterpretation higher than 50% in determining GDS and besides ignores displacement of gametes. A panoramic sweep across a complete transverse‐section of each gonad was validated as the best option for establishing GDS. This new methodology was tested on several polyplacophorans species, and seems generally applicable for histological assessment of reproductive cycle and reproductive season in polyplacophorans.     

Gonadal morphogenesis and sex differentiation in intraovarian embryos of the viviparous fish Zoarces viviparus (Teleostei, Perciformes, Zoarcidae): a histological and ultrastructural study

It is essential to know the timing and process of normal gonadal differentiation and development in the specific species being investigated in order to evaluate the effect of exposure to endocrine-disrupting chemicals on these processes. In the present study gonadal sex differentiation and development were investigated in embryos of a viviparous species of marine fish, the eelpout, Zoarces viviparus, during their intraovarian development (early September to January) using light and electron microscopy. In both sexes of the embryos at the time of hatching (September 20) the initially undifferentiated paired bilobed gonad contains primordial germ cells. In the female embryos, ovarian differentiation, initiated 14 days posthatch (dph), is characterized by the initial formation of the endoovarian cavity of the single ovary as well as by the presence of some early meiotic oocytes in a chromatin-nucleolus stage. By 30 dph, the endoovarian cavity has formed. By 44 dph and onward, the ovary and the oocytes grow in size and at 134 dph, just prior to birth, the majority of the oocytes are at the perinucleolar stage of primary growth and definitive follicles have formed. In the presumptive bilobed testis of the male embryos, the germ cells (spermatogonia), in contrast to the germ cells of the ovary, remain quiescent and do not enter meiosis during intraovarian development. However, other structural (somatic) changes, such as the initial formation of the sperm duct (30 dph), the presence of blood vessels in the stromal areas of the testis (30 dph), and the appearance of developing testicular lobules (102 dph), indicate testicular differentiation. Ultrastructually, the features of the primordial germ cells, oogonia, and spermatogonia are similar, including nuage, mitochondria, endoplasmic reticulum, and Golgi complexes.     

Habitat Patch Size,Facultative Monogamy and Sex Change in a Coral-dwelling Fish, <Emphasis Type="Italic">Caracanthus unipinna</Emphasis>

Synopsis We investigated the inter-relationships between coral colony size, social group size, mating system, and patterns of sex allocation in the pygmy coral croucher, Caracanthus unipinna (Caracanthidae), an obligate coral-dwelling fish. Histological examination of the gonads from all individuals in social groups revealed that the predominant mating system was harem polygyny. However, both group size and mating system co-varied with coral colony size, with pair forming and monogamy occurring on small corals and group forming and harem polygyny on large corals. This species therefore displays mating system plasticity in response to varying habitat patch size. Within-group sexual size dimorphism and individual gonad structure indicate that C. unipinna is also likely to be a protogynous hermaphrodite. These social and reproductive features of C. unipinna contrast with some other coral-dwelling fishes, which display a lack of social and mating system plasticity in response to habitat patch size, and either bi-directional or protandrous sex change. Possible reasons for this dichotomy include differences in spawning mode, parental care and levels of intrasexual aggression.     

Equivalent whole-body concentrations of 11-ketotestosterone in female and male coral goby Gobiodon erythrospilus, a bidirectional sex-changing fish

The relationship between whole-body concentrations of 11-ketotestosterone (11-KT) and sexual function was examined in the coral goby Gobiodon erythrospilus , a bi-directional sex-changing fish. 11-KT occurred in both female and male G. erythrospilus , but levels were not always higher in males than in females within heterosexual pairs, and were not related to the stage of gonadal development of individual fish. These results suggest that comparable 11-KT levels in both sexes may allow serial adult sex change to take place in bi-directional sex-changing species, such as Gobiodon spp.     

Gonadal morphology and difference in reproductive development of two isolated populations of Astyanax rivularis (Teleostei,Characidae)

Individuals of the same species may present different reproductive tactics depending on the environment in which they develop and mature. The present study aimed to define the gonadal development phases of males and females of Astyanax rivularis and to carry out a comparative analysis of the reproductive development of specimens captured in two isolated environments of the São Francisco River basin in Serra da Canastra, Brazil (Point 1: low vegetation and river showing calm and crystalline waters with small well formations; Point 2: current waters, and well-established areas of arboreal vegetation). Thus, the gonads of A. rivularis specimens were collected, fixed and processed with techniques for light microscopy. Five maturation phases of the females' reproductive cycle were established: immature, developing, spawning capable, regressing and regenerating. Three maturation phases of the males' reproductive cycle were observed: spawning capable, regressing, and regenerating. There are differences in the phases of gonadal development of A. rivularis between the two sampling points so that, possibly, animals upstream of the waterfall demonstrate a delay in the reproductive cycle in relation to animals downstream.     

Reproductive biology and larval development of the terapontid Amniataba caudavittata, including comparisons with the reproductive strategies of other estuarine teleosts in temperate Western Australia

Samples collected monthly from the Swan Estuary between March 1978 and May 1979, together with environmental data for 1977 to 1980, have been used to elucidate various aspects of the reproductive biology of Amniataba caudavittata in this estuary. The gonads of A. caudavittala started to develop rapidly in the spring, when day length, water temperatures and salinities were increasing markedly. Spawning, which occurred mainly towards the top end of the upper estuary, was initiated in November, when water temperatures and salinities in that region were c. 24° C and 9‰, and it peaked in December/January when they were c. IT C and 17%○, Maturity is attained by at least the majority offish at the end of the second and each subsequent year of life. Although some of the larger 1-year-old fish attained maturity, this occurred in only one of the two tributary rivers, possibly reflecting differences in the salinity regimes in these rivers. Fecundities ranged from 50 000 in a 150-mm fish to 705 000 in a 254-mm fish, with a mean of 310 000. The mature, unfertilized eggs are small and spherical and have a diameter of 560 μm. The larvae are pelagic and characterized by an elongate body, which becomes moderately deep and laterally compressed during development, a short to moderate, tightly-coiled gut, a distinct gap between the anus and the origin of the anal fin and 25 or 26 myomeres. The development of fins and settlement of A. caudavittata larvae occurs at a smaller size than in the larvae of other terapontid species previously described. The success of A. caudavittata in the Swan Estuary can be attributed in part to its production of very large numbers of eggs at a time when, due to low fresh water discharge and a smait tidal range, conditions in the estuary are relatively stable. Comparisons between the biology of A. caudavittata and that of other abundant teleosts that spawn in south-western Australian estuaries show that these species exhibit a wide range of reproductive strategies.     

Testing a new version of the size-advantage hypothesis for sex change: sperm competition and size-skew effects in the bucktooth parrotfish, Sparisoma radians

A variety of field studies suggest that sex change in animalsmay be more complicated than originally depicted by the size-advantagehypothesis. A modification of the size-advantage hypothesis,the expected reproductive success threshold model, proposesthat sperm competition and size-fecundity skew can stronglyaffect reproductive pay-offs. Size-fecundity skew occurs ifa large female's fecundity is markedly higher than the aggregateof the other members of her social group and, together withpaternity dilution from sperm competition, can produce situationsin which large females benefit by deferring sex change to smallerfemales. Deferral by large females can create sex-size distributionscharacterized by the presence of large females and small sex-changedmales, and it is precisely these distributions that the traditionalsize-advantage model cannot explain. We tested the predictionsof the new model with the bucktooth parrotfish, Sparisoma radians,on coral reefs in St. Croix, U.S. Virgin Islands. Collectionsand spawning observations determined that the local environmentalregime of S. radians is characterized by pervasive sperm competition(accompanying 30% of spawns) and factors that can produce substantialsize-fecundity skew in social groups. Dominant male removalexperiments demonstrate that the largest females in social groupsoften do not change sex when provided an opportunity. Instead,smaller, lower-ranking females change sex when a harem vacancyarises. This pattern of sex change is in contrast to virtuallyall previous studies of social control of sex change in fishes,but provides strong support for the general predictions of theexpected reproductive success threshold model.