Ovarian development and serum sex steroid and vitellogenin profiles in the female cultured sturgeon hybrid, the bester

Changes in serum levels of estradiol-17/J (E₂), testosterone (T), 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) and vitellogenin (VTG), in cultured adult female bester were examined in relation to ovarian development during a 1-year sampling period. Considerable variations in oocyte development were found among fish. Oocytes at previtellogenic stage (≥0–6mm in diameter) generally started to develop concomitantly with the degeneration of the first batch of oocytes. In vitellogenic individuals, ovaries were comprised of more advanced oocytes with diameter ranging from 0–6 to 2–6 mm and in the post-vitellogenic class, oocytes attained their largest size (>2–6mm) while the germinal vesicle was migrating towards the animal pole. Oocytes with a migrating nucleus were maintained during the winter period and massive degeneration started in April–May without germinal vesicle breakdown (GVBD) or ovulation occurring. Seasonal changes in E₂, T and VTG levels were well correlated with the advancement of oogenesis. Their levels increased during vitellogenesis, whereas in the post-vitellogenic (migratory nucleus) stage the levels of E₂ declined from 2–4 ng ml ^?1± to 1–2 ng ml ^?1 and VTG from 4–10 mg ml ^?1 to 0.–0.5 mg ml ^?1 while T levels remained high (50–60 ng ml ^?1). In contrast, serum levels of 17,20?-P were constantly low (less than 0.2 ng ml^?L) throughout the reproductive cycle. These results indicate that the time appropriate for induction of artificial reproduction would be from October–November to April–May when the oocytes are in the late Stages of the development.     

Early sex identification of 18‐month cultured beluga sturgeon (Huso huso) using ultrasonography,small surgery and plasma steroid hormones

Since sturgeons do not show clear sexual dimorphism particularly when are small in size, attempts were made to determine the best methods to identify early sex in farmed beluga sturgeon (Huso huso). The present study describes the ultrasonography, small surgery and plasma steroid hormone methods to determine gender at 18‐month fish, which no research has been conducted yet into the fish at such small ages. Twenty one cultured beluga sturgeon's gonad were imaged using an ultrasonograph unit with a 9–13 MHz linear transducer. Overall accuracy of sex determination using ultrasonography was 80.95%. Plasma testosterone (T) levels were significantly higher in males than in females whereas 17α,20βOH‐P levels were significantly higher in females than in males. Testosterone (T) and 17α,20βOH‐P were not correlated with morphometric parameters (TL, SL, W, CF) in 18‐month beluga sturgeon. Results of this study indicated that sex could be identified by each of ultrasonography, small surgery and analysis of blood plasma in such a small size (18‐month). Although direct observation was more efficient than the other methods, ultrasonography was the simplest and cost‐effective tool in sturgeon's sex determination compared to other methods, and the least invasive.     

Effects of constant short and long photoperiod regimes on the spawning performance and sex steroid levels of female and male sea bass

Under constant short photoperiod, the spawning time of 2-year-old sea bass Dicentrarchus labrax was advanced as compared to controls, whereas spawnings were delayed under constant long photoperiod. High plasma levels of 17β-oestradiol (E_2/) and testosterone (T) in females were coincident with the appearance of vitellogenic oocytes in the ovary, while high levels of 11-ketotestosterone (11-KT) and T in males were coincident with the presence of spermiating males. Although plasma levels of E₂ in females and 11-KT in males were low during the remainder of the cycle, levels of T were always >1 ng ml⁻¹ in both sexes, suggesting that T could play an important role during the initial stages of gonadal development. The profiles of E₂ and T in females and 11-KT and T in males exposed to constant short days were similar to those in the control group, but fish which were maintained under constant long photoperiods showed a bimodal pattern of these steroids. The results obtained from fish exposed to constant photoperiod regimes provide further evidence that an endogenous process could be operating to control the reproduction of sea bass.     

Sex steroids, growth and condition of Arctic charr broodstock during an annual cycle

Changes in plasma concentrations of sex steroids, growth rate and condition of repeat spawning (3+) male and female Arctic charr were studied throughout an annual reproductive cycle. Individually marked fish (mean weight approx. 500 g) were held under conditions of liberal food supply, constant temperature (4° C) and simulated natural photoperiod (Tromsø, 70° N). Once each month fish were weighed, measured and blood samples taken for steroid analysis. Plasma concentrations of testosterone (T), 11-ketotestosterone (11-KT) and oestradiol-17β (E₂) were determined using radioimmunoassay (RIA). Both male and female fish displayed distinct seasonal changes in plasma concentrations of sex steroids, growth rate and condition. From February (minimal concentrations) to March all sex steroids increased slightly and these elevated concentrations were maintained until May. Thereafter, there was a second, and far more pronounced, increase in plasma steroid concentrations which culminated in peak steroid concentrations in September–October. There was then a rapid decline during the spawning period. In winter, growth rate and condition were generally low, then increased during the spring, reached a peak during the summer, and then declined with the onset of autumn. During spring (March–May), the frequency distributions of plasma testosterone concentrations in both male and female fish were bimodal. The fish of the upper modal group of the distribution had significantly higher growth rates and condition than those in the lower modal group. In summer and early autumn (June–September) the association between T and growth rate changed. Significant negative correlations between T and growth rates were observed in females. There was an increase in endocrine activity, indicated by elevated plasma sex steroid concentrations in March, 7–8 months prior to maturation. It is suggested that this may be one factor influencing the onset of spring growth and energy deposition among maturing charr.     

Testicular development and serum levels of gonadal steroids during the annual reproductive cycle of captive Japanese sardine

Gonad and blood samples were taken throughout the year from captive males of the Japanese sardine,Sardinops melanostictus, and changes in serum levels of gonadal steroids were examined in relation to the annual gonadal cycle. On the basis of testicular histology, the annual gonadal cycle was divisible into four periods: immature (July–September), spermatogenesis (October–December), spermiation (January–April), and post-spawning (May–June). The pattern of seasonal changes in the gonadosomatic index (GSI) was inversely correlated with that of water temperature, and reflected the degree of testicular maturity. The serum testosterone level was relatively low during spermatogenesis (2.2–2.5 ng/ml), rose markedly around the time of spermiation (7.7–24.6 ng/ml), and became low after spawning and during immature periods (0.6–0.7 ng/ml). The serum 17α,20β-dihydroxy-4-pregnen-3-one level was high in males with spermatogenic or spermiating testes (0.6–1.0 ng/ml), but became low (0.2 ng/ ml during the post-spawning period and was undetectable in immature fish. Although 11-ketotestosterone was detectable in some fish, the values obtained were thought to reflect cross-reactivity of the antiserum employed with testosterone. These findings are discussed in relation to male reproduction of the Japanese sardine and steroidal regulation of spermatogenesis and spermiation in other teleosts.     

Lunar synchronization of testicular development and plasma steroid hormone profiles in the golden rabbitfish

Weekly changes in the gonadosomatic index (I_G) of male golden rabbitfish Siganus guttatus showed two peaks corresponding with the new moons in June and July. The testes developed synchronously toward the first lunar quarter in June and July. After the second spawning, the sperm duct and the seminiferous tubules were occupied by residual spermatozoa and spermatogonia, respectively. Weekly changes of plasma testosterone, 11-ketotestosterone and 17,20β-dihydroxy-4-pregnen-3-one coincided with those of testicular activity. They reached their peaks 1 week before spawning coinciding with the peaks of I_G and testicular development. These cyclical changes in plasma steroid hormones suggest that lunar periodicity is a major factor that synchronizes testicular activity of S. guttatus .     

Measurement of urinary and fecal steroid metabolites during the ovarian cycle in captive and wild Japanese macaques, Macaca fuscata

We measured the concentration of steroid hormones from urine, feces, and blood samples of two captive Japanese macaques, Macaca fuscata, during nonconceptive ovarian cycles to compare the patterns of the excreted steroids with those of circulating steroids. Urine and feces were analyzed for estrone conjugates (E1C) and pregnanediol-3-glucronide (PdG) using enzyme immunoassays (EIAs), while plasma was analyzed for estradiol-17beta(E2), progesterone (P), and luteinizing hormone (LH) using radioimmunoassays (RIAs). Urinary and fecal E1C and PdG levels were approximately parallel to plasma E2 and P levels, respectively. The E1C profiles of daily urinary and fecal samples revealed a midcycle peak, followed by a sustained PdG increase lasting up to two weeks from the E1C peak. A fecal E1C peak was one day later than the urinary E1C peak. One of the captive females exhibited a discrete plasma LH peak, one indicator that ovulation has occurred, on the day following the urinary E1C peak, i.e., the same day of fecal E1C peak. We measured excreted steroids in nine wild females and determined the timing of ovulation by comparing fecal steroid profiles to those obtained in captive monkeys. Data from wild females indicated that eight of nine females conceived during their first ovulatory cycle of the sampling period, whereas the remaining female failed to conceive during the sampling period even though she ovulated. In the eight females that conceived, E1C increased again following the detected or estimated E1C peak, with levels comparable to the preovulatory peak levels, and sustained elevations of PdG for over 40 days. These data illustrate that the urinary and fecal profiles of ovarian steroid excretion obtained through the application of these noninvasive techniques provide an accurate approach for monitoring conceptive and nonconceptive ovarian cycle in captive and free-living Japanese macaques.     

Determination of sex and maturity stage of great sturgeon (Huso huso) using steroid sex hormones profiles,histology and laparoscopic images of gonads

We studied sex and maturity stage of great sturgeon with different reproductive stages using sex steroid hormones concentrations in blood plasma, gonad histology and laparoscopic technique. One hundred sixty farmed great sturgeons at ages between 1 and +12 years and weight ranged from 0.45 to 49.65 kg (80 males and 80 females, 20 fish of each maturity stage) were selected. Mean sex steroid levels showed that testosterone (T) and 11ketotestosterone (11KT) in plasma varied significantly by sex and maturity stage. But the mean concentrations of 17B‐estradiol (E2) varied significantly only between the maturity stages I and III. All fish were sex determined by laparoscopy and histology examinations confirmed it. Our results showed, however laparoscopy was effective method for sex determination at four maturity stages, but young fish at maturity stage I required gonadal histology examinations to confirm sex. The present study results showed that some steroid sex hormones (T and 11KT) can be used to determine sex and reproductive stage in great sturgeon, especially in later maturity stages. Although the laparoscopy may be stressful and cause small scars on the body of the fish, but it is a fast, effective, and cheap method for sex and maturity stage assessment (30 to 40 s for each fish), especially at later maturity stages. Histology of gonads is a very accurate, but it is an invasive method and not a suitable technique for commercial purposes. Histology is more suited for scientific studies than commercial application. The ability to use minimally invasive methods for sex determination will assist broodstock management and conservation in sturgeons.     

Operational sex ratio, sexual conflict and the intensity of sexual selection

Modern sexual selection theory indicates that reproductive costs rather than the operational sex ratio predict the intensity of sexual selection. We investigated sexual selection in the polygynandrous common lizard Lacerta vivipara . This species shows male aggression, causing high mating costs for females when adult sex ratios (ASR) are male-biased. We manipulated ASR in 12 experimental populations and quantified the intensity of sexual selection based on the relationship between reproductive success and body size. In sharp contrast to classical sexual selection theory predictions, positive directional sexual selection on male size was stronger and positive directional selection on female size weaker in female-biased populations than in male-biased populations. Thus, consistent with modern theory, directional sexual selection on male size was weaker in populations with higher female mating costs. This suggests that the costs of breeding, but not the operational sex ratio, correctly predicted the strength of sexual selection.     

Histochemical detection of steroid synthesizing cells in the testes of goldfish,Carassius auratus,during the annual reproductive cycle

We investigated the sites of Δ⁵-3β-hydroxysteroid dehydrogenase (3 β-HSD) and glucose-6-phosphate dehydrogenase (G-6-PD) synthesis in the testes of goldfish, Carassius auratus, during the annual reproductive cycle. The histochemistry of fish gonads has been investigated previously in many species other than goldfish. The reproductive cycle of goldfish, is divided into five stages and the steroid synthesizing cells of the testes were studied during these stages, using histochemical techniques. We found that interstitial cells and seminiferous tubules are the main steroid synthesizing sites in testes of goldfish, and that enzyme activity was more intense in the interstitial cells than in the seminiferous tubules. During the pre-spawning months, 3 β-HSD and G-6-PD activities were weak compared to the spawning months.     

Regulators of male and female sexual development are critical for the transmission of a malaria parasite

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Reproductive features and gonad development cycle of the soft bottom-gravel gorgonian Leptogorgia sarmentosa (Esper, 1791) in the NW Mediterranean Sea

Abstract

Leptogorgia sarmentosa (Cnidaria: Octocorallia) is a common soft bottom-gravel gorgonian in the northwestern Mediterranean Sea. This study examined the annual reproductive cycle of a L. sarmentosa. population at a depth of 30 m, and further determined the sex ratio, the intra-colonial gonadal output variability and the age at first reproduction. L. sarmentosa was gonochoric and the population studied was characterized by a sex ratio slightly biased towards female colonies (1 male:1.6 female). Secondary branches had higher polyp fertility (number of gonads per polyp) compared to primary branches, but because of the number of polyps on the former, most of the sexual effort was actually contributed by the primary branches, as in other gorgonian species. Male colonies became fertile above a height of 21 cm, but female colonies had gonads even in the 1–10 cm height class. Spawning occurred between late August and early September, although there was no direct observation of broadcast spawning or surface brooder strategy. The maximum gonad size was 550 μm in males and 500 μm in females, with a mean diameter of 270 μm for spermaries, and 190 μm for eggs. The number of gonads per polyp prior to spawning reached 4–5 spermaries polyp!1 in male colonies, and 3–4 eggs polyp!1 in female colonies. Spawning did not appear to be synchronized with the full moon. L. sarmentosa appeared to have a different reproductive strategy to other Mediterranean gorgonians (living on hard bottom substrata), probably because of its different habitat preferences and biological (morphology, diet, prey capture rates, growth, biochemical levels) features.     

Role of brain hormone in oogenesis of the Indian freshwater leech,Poecilobdella viridis (Blanchard) during the annual reproductive cycle

The possible role of a brain hormone in oogenesis of Poecilobdella viridis has been investigated by brain extirpation and brain extract injections during non-reproductive (November to January) and reproductive (March to May) periods. Brain extirpation during the non-reproductive period ceased maturation of the ovary. It is inferred that brain secretion bears possibly a gonadotropic principle which governs and regulates the oogenesis during the annual reproductive cycle.     

Inhibition of spawning and associated suppression of sex steroid levels during confinement in the substrate-spawning Tilapia zillii

Substrate-spawning Tilapia zillii failed to spawn in crowded holding tanks but exhibited a marked tendency to spawn soon after transfer to individually partitioned aquaria. Confined conditions suppressed the levels of serum 17 β -oestradiol (E₂) and testosterone (T) in females, which remained low throughout the period of confinement. Levels of both steroids rose significantly following transfer of fish to individual aquaria and were maintained at consistently higher levels than those of fish which remained confined. Proportions of stage 3 (late perinucleolar) oocytes were significantly lower ( P <0.001) in individual fish 21–30 days after transfer, coincident with significantly higher ( P <0.01) proportions of stage 6 or 7 oocytes (late vitellogenic or maturing oocytes). However, no significant differences ( P ≥0.05) were detected between individual or confined groups of fish in the relative proportions of stage 2 (early perinucleolar), stage 4 (cortical alveolar) or stage 5 (early vitellogenic) oocytes. Atresia increased as the period of confinement increased. Following return of individual fish to confined conditions, blood steroids fell rapidly to levels seen in fish that had remained confined throughout. It is suggested that the reduced sex steroid levels detected during confinement were insufficient to allow developing oocytes to complete oocyte growth and maturation. The detection of significantly lower proportions of stage 3 and significantly higher proportions of stage 6/7 oocytes soon after transfer suggest that fish were preparing one batch of oocytes for spawning (stage 6/7 oocytes) whilst recruiting from a pool of previtellogenic oocytes (stage 3) for the ensuing spawning cycle.     

Freemartin in the amphibian Pleurodeles waltl: parabiosis between individuals from opposite sex triggers both germ and somatic cells alterations during female gonad development

Wild type embryos of the newt Pleurodeles waltl were used to realize parabiosis, a useful model to study the effect of endogenous circulating hormones on gonad development. The genotypic sex of each parabiont (ZZ male or ZW female) was determined early from the analysis of the sex chromosome borne marker peptidase-1. In ZZ/ZZ and ZW/ZW associations, gonads develop according to genetic sex. In ZZ/ZW associations, the ZZ gonads differentiate as normal testes while ZW gonads development shows numerous alterations. At the beginning of sex differentiation, these ZW gonads possess a reduced number of germ cells and a reduced expression of steroidogenic factor 1 and P450-aromatase mRNAs when compared to gonads from ZW/ZW associations. During gonad differentiation, conversely to the control situation, these germ cells do not enter meiosis as corroborated by chromatin status and absence of the meiosis entry marker DMC1; the activity of the estradiol-producing enzyme P450-aromatase is as low as in ZZ gonads. At adulthood, no germ cells are observed on histological sections, consistently with the absence of VASA expression. At this stage, the testis-specific marker DMRT1 is expressed only in ZZ gonads, suggesting that the somatic compartment of the ZW gonad is not masculinized. So, when exposed to ZZ hormones, ZW gonads reach the undifferentiated status but the ovary differentiation does not occur. This gonad is inhibited by a process affecting both somatic and germ cells. Additionally, the ZW gonad inhibition does not occur in the case of an exogenous estradiol treatment of larvae.     

Seasonal migrations and reproductive patterns in the lake sturgeon, Acipenser fulvescens, in the vicinity of hydroelectric stations in northern Ontario

This study was conducted in order to evaluate seasonal migratory behaviour and reproductive pattern of lake sturgeon in a confined region of the Mattagami River system in northern Ontario where river flow is regulated by hydroelectric works. Radio tracking and the systematic sampling of lake sturgeon using gill nets indicated that the distribution of fish throughout the study site varied on a seasonal basis. This distribution was related to the migration of individuals to potential spawning sites in the spring, a post-spawning dispersal to feeding areas and late summer migration to an area of concentration on the Groundhog River which is a tributary of the Mattagami River. There was a high proportion of fish (about 50%), within the size range of reproductively active fish, found in the vicinity of suitable spawning habitat during early May. Measurement of the gonadosomatic index (GSI) and plasma sex steroid hormone levels revealed a divergent pattern of reproductive development between the sexes. Female sturgeon exhibited a prolonged period of ovarian regression following spawning. Resumption of ovarian development was not evident until September and was characterized by an increased GSI and plasma levels of testosterone and 17β-estradiol. In contrast, male lake sturgeon began testicular recrudescence within one month of spawning with the GSI reaching prespawning levels by September; reproductive hormones were at prespawning levels by the end of June. It seems that hydroelectric works has complex effects on sturgeon in the Mattagami system. The extensive migratory behaviour of lake sturgeon within the study area make it prone to impingement or entrainment whereas the altered river flow appears to enhance reproductive development. This revised version was published online in August 2006 with corrections to the Cover Date.     

Annual reproductive cycle and condition index of Mactra corallina (Mollusca: Bivalvia) from the north coast of Tunisia

This work aims to examine the reproductive cycle of the bivalve Mactra corallina inhabiting the Gulf of Tunis (Tunisia). Histological analysis indicated that the reproductive cycle is composed of six stages and was synchronous between sexes. Gonadal development began in January. From April to July, an increase in temperature (from 16 to 28°C) and a rise in chlorophyll a (from 3.25 to 6.35 mg/L) marked the period of sexual maturity in both sexes, which was also confirmed by an elevation in condition index (CI). Partial spawning started in April for males and in May for females, peaking in late summer indicating a prolonged reproductive period. The reproductive cycle of M. corallina finished with an inactive stage during autumn. From the total number of animals used in this study, we identified 104 females (52%) and 96 males (48%) corresponding to a sex ratio 1:0.92 that did not differ significantly from a 1:1 ratio.     

Genetics of hybrid male sterility among strains and species in the Drosophila pseudoobscura species group

Taxa in the early stages of speciation may bear intraspecific allelic variation at loci conferring barrier traits in hybrids such as hybrid sterility. Additionally, hybridization may spread alleles that confer barrier traits to other taxa. Historically, few studies examine within- and between-species variation at loci conferring reproductive isolation. Here, we test for allelic variation within Drosophila persimilis and within the Bogota subspecies of D. pseudoobscura at regions previously shown to contribute to hybrid male sterility. We also test whether D. persimilis and the USA subspecies of D. pseudoobscura share an allele conferring hybrid sterility in a D. pseudoobscura bogotana genetic background. All loci conferred similar hybrid sterility effects across all strains studied, although we detected some statistically significant quantitative effect variation among D. persimilis alleles of some hybrid incompatibility QTLs. We also detected allelism between D. persimilis and D. pseudoobscura USA at a second chromosome hybrid sterility QTL. We hypothesize that either the QTL is ancestral in D. persimilis and D. pseudoobscura USA and lost in D. pseudoobscura bogotana, or gene flow transferred the QTL from D. persimilis to D. pseudoobscura USA. We discuss our findings in the context of population features that may contribute to variation in hybrid incompatibilities.