The relationships between gonad development and sex steroid levels at different ages in Acipenser schrenckii

The histological developments of the gonad and the associated sex steroid levels were determined in the breeding stocks of Acipenser schrenckii (age classes 1 to 5) maintained under natural temperature regimes (December 4°C; August 26°C). Early sex differentiation was observed in 1‐year‐old fish, while testosterone (T) and 17β‐estradiol (E₂) levels ranged from T 1.1 to 3.4 nmol l^?1 (average 1.8 nmol l^?1), and E₂ varied from 24 to 85 pmol l^?1 (av. 50.3 pmol l^?1). Gonadal status of 2‐year‐old males was in stage II while ovaries were at stage I, exhibiting T levels from 1.2 to 4.4 nmol l^?1 (av. 2.2 nmol l^?1), and E₂ concentrations from 10 to 97 pmol l^?1 (av. 38.9 pmol l^?1). At the age of 3 years, the testes in males were at developmental stage III while the ovaries remained in stage I, with T levels ranging from 1.3 to 21.7 nmol l^?1 (av. 9.6 nmol l^?1), and E₂ concentrations ranging from 17 to 108 pmol l^?1 (av. 44.8 pmol l^?1). At the age of 4 years, testes in males were at developmental stage III while ovaries in females had reached stage II, with T concentrations ranging from 7.3 to 52.6 nmol l^?1 (av. 26.3 nmol l^?1), and E₂ levels between 13 and 86 pmol l^?1 (average 55.3 pmmol l^?1). In 5‐year‐old fish, the testes reached maturity stage while the ovaries were mostly in stage III, with T values from 5.7 to 44.2 nmol l^?1 (av. 13.9 nmol l^?1), and E₂ concentrations from 21 to 453 pmol l^?1 (av. 137.7 pmol l^?1). Data demonstrated large differences in sex steroid levels among immature Amur sturgeon, and testicular maturation occurred earlier than ovarian maturation.     

Morphometric relationship of length–weight and chelae length–width of eastern white river crayfish (Procambarus acutus acutus, Girard, 1852), under culture conditions

Length–weight (TL vs WWT) and chelae length–width (ChL vs ChW) relationships were described for juveniles, males and females, and for form I and form II males of Procambarus acutus acutus. The length–weight relationships for juveniles, form I, form II males, and females could be described as: WWT = 5 × 10⁻³ TL^3.09, WWT = 6 × 10⁻³ TL^3.61, WWT = 6 × 10⁻⁹ TL^3.26, and WWT = 6 × 10⁻⁴ TL^3.5, respectively. In all forms, growth was allometric (P < 0.05). The ancova test indicated that slopes and intercepts of the length–weight regressions were significantly different between sex and sexual stages. The regressions for chelae length–width relationships for form I and form II males, and females were: ChW = −0.81 + 0.27CL, ChW = −0.33 + 0.25CL, and ChW = −0.82 + 0.32CL, respectively. Although the slope and intercepts of regressions for ChL and ChW were similar for those of form I and form II males, the slopes and intercepts of regressions of females were significantly different from form I and form II males. No statistical difference was observed in mean ChL between form II males and females (P > 0.05), but a significant difference was detected in mean ChL between form I and form II males (P < 0.05) and form I and females (P < 0.05). Form I males had longer ChL than form II males and females. The same trend was observed in mean ChW for form I and form II males, but a significant difference was detected between form II males and females (P < 0.05). In addition, results indicated that chelae lengths and widths increased allometrically with total length (TL) for both sex and sexual stages.     

Characterization of a hormone receptor defect in the androgen-insensitivity mutant

Mouse kidney cytosol contains specific receptors that reversibly bind dihydrotestosterone at a concentration of 43 f moles/mg protein. [Nonstandard abbreviation: DHT, dihydrotestosterone, 17 β-hydroxy-5 α-androstan-3-one.] The equilibrium dissociation constant of the receptor-dihydrotestosterone complex is 1.3 × 10^?9M for females and 1.7 × 10^?9M for castrated males. The complex sediments at 8–9S in glycerol gradients. In males bearing the androgen-insensitivity mutation (analogous to human testicular feminization), the specific dihydrotestosterone receptor activity is decreased about 8 fold. The residual binding activity has wild type affinity (K_D = 1.5 × 10^?9M) for dihydrotestosterone and also sediments at 8–9S. Kidney cytosol from castrated mutant mice displays a new binding component with low affinity and high capacity for dihydrotestosterone.     

A single injection of 17 beta-estradiol facilitates sexual behavior in castrated male mice

Sexual behavior was assessed in castrated adult CD-1 male mice given exogenous steroids under various treatment regimens. Castrated mice maintained on 20 μg testosterone (T) daily for 1 week, but given 250 μg testosterone propionate (TP) on the day of testing showed higher levels of copulatory activity than intact mice or the males receiving an additional dose of 20 μg T on the test day, although plasma testosterone levels were not different at the time of behavioral testing. Castrated males given 50, 125, or 250 μg TP for 1 week including the day of testing showed higher levels of sexual behavior than males receiving the same doses of TP only once, on the test day. A single injection of 17β-estradiol (E₂) completely restored the male copulatory pattern, including ejaculation, in castrated mice under every condition examined. Testosterone and dihydrotestosterone (DHT) were less effective than E₂, as was the combination of E₂ and DHT. The relative efficacy of a single dose of T, DHT, and E₂ plus DHT was dependent upon factors such as the delay between steroid administration and testing, as well as whether or not the castrated mice received androgen replacement prior to testing. Estradiol benzoate (E₂B) was not capable of restoring sexual behavior in castrated mice in this study. The comparison of results obtained with TP, T, E₂, and E₂B suggests that an appreciable, but not necessarily sustained, elevation of E₂ levels in the brain may be critical in the facilitation of male copulatory behavior in mice.     

Intra‐ and Intersexual swim bladder dimorphisms in the plainfin midshipman fish (Porichthys notatus): Implications of swim bladder proximity to the inner ear for sound pressure detection

The plainfin midshipman fish, Porichthys notatus , is a nocturnal marine teleost that uses social acoustic signals for communication during the breeding season. Nesting type I males produce multiharmonic advertisement calls by contracting their swim bladder sonic muscles to attract females for courtship and spawning while subsequently attracting cuckholding type II males. Here, we report intra‐ and intersexual dimorphisms of the swim bladder in a vocal teleost fish and detail the swim bladder dimorphisms in the three sexual phenotypes (females, type I and II males) of plainfin midshipman fish. Micro‐computerized tomography revealed that females and type II males have prominent, horn‐like rostral swim bladder extensions that project toward the inner ear end organs (saccule, lagena, and utricle). The rostral swim bladder extensions were longer, and the distance between these swim bladder extensions and each inner‐ear end organ type was significantly shorter in both females and type II males compared to that in type I males. Our results revealed that the normalized swim bladder length of females and type II males was longer than that in type I males while there was no difference in normalized swim bladder width among the three sexual phenotypes. We predict that these intrasexual and intersexual differences in swim bladder morphology among midshipman sexual phenotypes will afford greater sound pressure sensitivity and higher frequency detection in females and type II males and facilitate the detection and localization of conspecifics in shallow water environments, like those in which midshipman breed and nest.     

A single injection of 17β-estradiol facilitates sexual behavior in castrated male mice

Sexual behavior was assessed in castrated adult CD-1 male mice given exogenous steroids under various treatment regimens. Castrated mice maintained on 20 μg testosterone (T) daily for 1 week, but given 250 μg testosterone propionate (TP) on the day of testing showed higher levels of copulatory activity than intact mice or the males receiving an additional dose of 20 μg T on the test day, although plasma testosterone levels were not different at the time of behavioral testing. Castrated males given 50, 125, or 250 μg TP for 1 week including the day of testing showed higher levels of sexual behavior than males receiving the same doses of TP only once, on the test day. A single injection of 17β-estradiol (E₂) completely restored the male copulatory pattern, including ejaculation, in castrated mice under every condition examined. Testosterone and dihydrotestosterone (DHT) were less effective than E₂, as was the combination of E₂ and DHT. The relative efficacy of a single dose of T, DHT, and E₂ plus DHT was dependent upon factors such as the delay between steroid administration and testing, as well as whether or not the castrated mice received androgen replacement prior to testing. Estradiol benzoate (E₂B) was not capable of restoring sexual behavior in castrated mice in this study. The comparison of results obtained with TP, T, E₂, and E₂B suggests that an appreciable, but not necessarily sustained, elevation of E₂ levels in the brain may be critical in the facilitation of male copulatory behavior in mice.     

THE OXIDATION-REDUCTION POTENTIAL OF THE LUCIFERIN-OXYLUCIFERIN SYSTEM

The oxidation-reduction potential of the Cypridina luciferin-oxyluciferin system determined by a method of "bracketing" lies somewhere between that of anthraquinone 2-6-di Na sulfonate (E_o ^'' at pH of 7.7 = –.22) which reduces luciferin, and quinhydrone (E_o ^'' at pH of 7.7 = +.24), which oxidizes luciferin. Systems having an E_o ^'' value between –.22 and +.24 volt neither reduce oxyluciferin nor oxidize luciferin. If the luciferin-oxyluciferin system were truly reversible considerable reduction and oxidation should occur between –.22 and +.24. The system appears to be an irreversible one, with both "apparent oxidation" and "apparent reduction potentials" in Conant''s sense. Hydrosulfites, sulfides, CrCl₂, TiCl₃, and nascent hydrogen reduce oxyluciferin readily in absence of oxygen but without luminescence. Luminescence only appears in water solution if luciferin is oxidized by dissolved oxygen in presence of luciferase. Rapid oxidation of luciferin by oxygen without luciferase or oxidation by K₃Fe(CN)₆ in presence of luciferase but without oxygen never gives luminescence.     

Seasonal plasticity of brain aromatase mRNA expression in glia: divergence across sex and vocal phenotypes

Although teleost fishes have the highest levels of brain aromatase (estrogen synthase) compared to other vertebrates, little is known of its regulation and function in specific brain areas. Previously, we characterized the distribution of aromatase in the brain of midshipman fish, a model system for identifying the neural and endocrine basis of vocal-acoustic communication and alternative male reproductive tactics. Here, we quantified seasonal changes in brain aromatase mRNA expression in the inter- and intrasexually dimorphic sonic motor nucleus (SMN) and in the preoptic area (POA) in males and females in relation to seasonal changes in circulating steroid hormone levels and reproductive behaviors. Aromatase mRNA expression was compared within each sex throughout non-reproductive, pre-nesting, and nesting periods as well as between sexes within each season. Intrasexual (male) differences were also compared within the nesting period. Females had higher mRNA levels in the pre-nesting period when their steroid levels peaked, while acoustically courting (type I) males had highest expression during the nesting period when their steroid levels peaked. Females had significantly higher levels of expression than type I males in all brain areas, but only during the pre-nesting period. During the nesting period, non-courting type II males had significantly higher levels of aromatase mRNA in the SMN but equivalent levels in the POA compared to type I males and females. These results demonstrate seasonal and sex differences in brain aromatase mRNA expression in a teleost fish and suggest a role for aromatase in the expression of vocal-acoustic and alternative male reproductive phenotypes.     

Quantitative histochemistry of the lysosomal dipeptidyl aminopeptidase II in the proximal tubule of the rat kidney

Summary The activity of the lysosomal dipeptidyl aminopeptidase II (DAP II) was measured by quantitative histochemical methods in the S₁/S₂ segments of the proximal tubule using freeze dried and celloidin mounted cryostat sections (FDC sections) of rat kidney. The methodological studies show that there is a linear relationship between the amount of reaction product and reaction time for the first 5 min, as well as section thickness between 4 and 10 m. Maximal DAP II activities were demonstrated at pH 5.5. The K _m of DAP II was about 2.3 mM. — In addition to the methodological studies, DAP II activity was also measured in the proximal tubule (S₁/S₂ segments) of experimental animals (sham-operated and castrated male and female rats). Sham-operated females showed significantly higher DAP II activities than males. DAP II activity increased significantly in castrated males so that there were no significant differences between castrated males, sham-operated and castrated females. The quantitative histochemical results are largely in agreement with biochemical data published earlier.Supported by the Deutsche Forschungsgemeinschaft (SFB 105)Dedicated to Prof. Dr. T.H. Schiebler, Chairman of the Institute of Anatomy of the University of Würzburg, on the occasion of his 60th birthday     

Nonsequential developmental trajectories lead to dimorphic vocal circuitry for males with alternative reproductive tactics

Midshipman fish, Porichthys notatus, have two male reproductive morphs: type I males generate long duration advertisement calls (“hums”) to attract females to a nest; type II males sneak-spawn and, like females, do not produce mate calls but generate short duration agonistic calls. A vocal pacemaker circuit includes: motoneurons in the caudal brain stem and rostral spinal cord that innervate vocal/sonic muscles; pacemaker neurons that are located ventrolateral to motoneurons and establish their fundamental discharge frequency; and a ventral medullary nucleus that couples the motoneuron-pacemaker circuit bilaterally. Transneuronal biocytin transport identified morph-specific developmental trajectories for the vocal circuit. Among nonreproductive, juvenile type I males, motoneuron soma size and motor nucleus volume increase most during a stage prior to sexual maturation. An additional increase in motoneuron size and nucleus volume is coupled to the greatest increase in pacemaker soma size at a stage coincident with the onset of sexual maturity; ventral medullary neurons show similar growth increments during both stages. Type II males (and females) mature with no or little change in cell size or motor nucleus volume. The results indicate that alternative mating tactics are paralleled by alternative developmental trajectories for the neurons that determine tactic-specific behaviors, in this case vocalizations. Together with aging data based on otolith growth, the results support the hypothesis that alternative male morphs in midshipman fish adopt nonsequential, mutually exclusive life history tactics. © 1996 John Wiley & Sons, Inc.     

Effect of zooplankton type and abundance on prey consumption by the fairy shrimp, Streptocephalus proboscideus (Anostraca: Crustacea)

Laboratory cultured Streptocephalus proboscideus (three sizes (mm), viz. 8.44 ± 0.95 (virgin), 14.18 ± 1.49 (adult I) and 19.24 ± 1.52 (adult II)) were offered (separately for males and females) field collected zooplankton (12 prey types) at three levels of abundance (1.0 ml⁻¹, 2.0 ml⁻¹ and 4.1 ind. ml⁻¹ in 30-minute feeding experiments. Gut contents, analyzed for abundance and diversity of prey type, showed that predator size, sex and their interaction had strong effects on prey consumption. Regardless of their size, and of prey density, S. proboscideus females consumed 25–90% more prey than males. Their filtration rates (adult II) were higher (125 ml ind.⁻¹ h.⁻¹) than those of males (30 ml ind.⁻¹ h.⁻¹) too. Rotifers had the highest numerical percentage in the gut, regardless of predator size or sex. Cladocerans were only consumed by adults I and II. Adult II females consumed 28.5–43.3 μg zooplankton dry weight ind.⁻¹ h.⁻¹. Size distribution of B. longirostris in the field and in the gut were closely similar. This study confirms S. proboscideus as a non-selective filter feeder. Since it did not eat jumping rotifers, copepod nauplii and copepodites, it may contribute to structuring its prey communities, because good escapers will be enriched in the medium, while poor escapers will be depleted.     

Differential effects of 11-ketotestosterone on dimorphic traits in a teleost with alternative male reproductive morphs

Species with dimorphic males typically have one morph (type I) associated with territoriality and courtship, and another morph (type II) associated with cuckoldry. In teleost fishes, type I males generally have higher levels of the androgen 11-ketotestosterone (KT) than type II males. Is KT causal to phenotypic differences between morphs? We investigated this question in the midshipman fish (Porichthys notatus) in which type I males have detectable levels of KT during the breeding season, whereas levels in type II males are usually undetectable. Type I midshipman will either cuckold or hold territories and court females, whereas type II males are only known to cuckold. Acoustic courtship by type I's is supported by the sonic motor nucleus, which innervates a sound-producing sonic muscle. Type I males have larger sonic motor nuclei and larger sonic muscles than type II males, consistent with the more dynamic vocal repertoire of type I's. Here, we tested whether intraperitoneal KT implants in adult type II males would induce type I male-like traits in brain, sonic muscle, and behavior. Type II's treated with KT did not differ from blank-implanted type II's in sonic motor nucleus volume. Sonic muscle mass increased in KT-implanted type II's, but did not reach the relative mass naturally observed in type I's. While neither territoriality nor courtship were induced, cuckoldry behavior intensified in KT-implanted type II's. Thus, for some but not all characters, KT exaggerated the expression of already existing type II male traits rather than inducing the type I male-like traits of territoriality, courtship, and an expansive vocal motor system.     

Steroid accumulation in song nuclei of a sexually dimorphic duetting bird,the rufous and white wren

This study tested the hypothesis that the relative proportion of neurons that are hormone sensitive in avian song control nuclei is related to the basic motor ability to sing, whereas the absolute number of such neurons is related to the complexity of song behavior. Either [³H]testosterone (T) or estradiol (E₂) was injected into male and female rufous and white wrens (Thryothorus rufalbus), a tropical species in which females sing duets with males but have smaller song repertoires than males. Autoradiographic analysis indicated that there were no sex differences in the proportions of T or E₂ target cells in two song nuclei: the high vocal center (HVC) and the lateral portion of the magnocellular nucleus of the anterior neostriatum (IMAN). The density of labeled cells per unit volume of tissue did not differ between the sexes in either song nucleus. Males have larger song nuclei, however, which is consistent with their more complex song behavior, and therefore have a greater total number of hormone-sensitive neurons in these regions than do females. Comparison of these results with measures of hormone accumulation in zebra finches, canaries, and bay wrens supports the hypothesis presented. © 1996 John Wiley & Sons, Inc.     

Sexually dimorphic neuron addition to an avian song-control region is not accounted for by sex differences in cell death

Only male zebra finches sing, and several brain regions implicated in song behavior exhibit marked sex differences in neuron number. In one region, the high vocal center (HVC), this dimorphism develops because the incorporation of new neurons is greater in males than in females during the first several weeks after hatching. Although estrogen (E₂) exposure stimulates neuron addition in females, it is not known where (E₂) acts, or to what extent sexual differentiation influences the production, specification, or survival of HVC neurons. In the present study we first reassessed sex and (E₂)-induced differences in cell degeneration within the HVC using the TUNEL technique to identify cells undergoing DNA fragmentation indicative of apoptosis. HVC neuron number, as well as the density and number of TUNEL-labeled and pyknotic cells within the HVC were measured in normal 20- and 30-day-old males and females, and in 30-day-old females implanted with E₂ on posthatch day 18. Although HVC neuron number was greater in males than in females, and was masculinized in E₂ females, no group differences were evident in the absolute number of dying cells. These results indicate that sex differences in cell survival within the HVC do not entirely account for sexually dimorphic neuron addition to this region. Rather, sexual differentiation acts on some HVC neurons before they complete their migration and/or early differentiation. Although the migratory route of HVC neurons is not known, a large number of E₂ receptor-containing cells (ER cells) reside just ventromedial to the HVC and adjacent to the proliferative ventricular zone. Next, we investigated whether these ER cells contribute to early-arising sex differences in HVC neuron addition. By combining [³H] thymidine autoradiography with immunocytochemistry for ERs, we first established that ER-expressing cells are not generated during posthatch sexually dimorphic HVC neuron addition, and thus are not young HVC neurons that transiently express ERs during their migration. Furthermore, in 25-day-old birds we found no sex difference in the density of pyknotic cells among this group of ER cells, suggesting that these cells do not promote the differential survival of HVC neuronal precursors migrating through this region. Rather, ER cells or other cell populations may establish sex differences in HVC neuron number by creating dimorphisms in cellular specification. © 1997 John Wiley & Sons, Inc. J Neurobiol 33: 61–71, 1997     

Alternative Male Spawning Tactics and Acoustic Signals in the Plainfin Midshipman Fish Porichthys notatus Girard (Teleostei,Batrachoididae)

The plainfin midshipman Porichthys notatus has two male reproductive morphs, ‘Type I’ and ‘Type II’, which are distinguishable by their physical traits alone. Type I males are eight times larger in body mass than Type II males and have a six-fold larger relative sonic (vocal) muscle mass than Type II males. In contrast, the testicles of Type II males are seven times larger than those of Type I males. This study demonstrates morph-specific patterns of reproduction, including acoustic signals, for Type I and II males. Field censuses of nests showed that only Type 1 males maintained nests. Type II males and females transiently appeared in these nests in association with each other. Infra-red video and hydrophone recordings in aquaria showed that Type I males maintained nests and readily vocalized. Long-duration ‘hums’ and sequences of short-duration ‘grunts’ were produced during advertisement and agonistic contexts, respectively. Humming Type I males attracted females to their nests, pair-spawned, and then guarded egg clutches alone. By contrast, Type II males neither acoustically courted females nor maintained available nest sites, but rather ‘sneak-’ or ‘satellite-spawned’ at the nests of Type I males. Type II males infrequently produced low amplitude, short duration grunts that were similar in spectral, temporal and amplitude characteristics to the grunts of females. Type II males appear to be obligate sexual parasites of the nest-building, mate-calling, and egg-guarding Type I males. The dimorphic body and vocal muscle traits of the two male morphs in the plainfin midshipman are thus paralleled by a divergence in their reproductive tactics and the properties of their acoustic signals.     

Evidence of latitudinal migration in tri-colored bats, Perimyotis subflavus

Background

Annual movements of tri-colored bats (Perimyotis subflavus) are poorly understood. While this species has been considered a regional migrant, some evidence suggests that it may undertake annual latitudinal migrations, similar to other long distance North American migratory bat species.

Methodology/Principal Findings

We investigated migration in P. subflavus by conducting stable hydrogen isotope analyses of 184 museum specimen fur samples and comparing these results (δD_fur) to published interpolated δD values of collection site growing season precipitation (δD_precip). Results suggest that the male molt period occurred between June 23 and October 16 and 33% of males collected during the presumed non-molt period were south of their location of fur growth. For the same time period, 16% of females were south of their location of fur growth and in general, had not travelled as far as migratory males. There were strong correlations between δD_fur from the presumed molt period and both growing season δD_precip (males – r ² = 0.86; p<0.01; females – r ² = 0.75; p<0.01), and latitude of collection (males – r ² = 0.85; p<0.01; females – r ² = 0.73; p<0.01). Most migrants were collected at the northern (>40°N; males and females) and southern (<35°N; males only) extents of the species'' range.

Conclusions/Significance

These results indicate a different pattern of migration for this species than previously documented, suggesting that some P. subflavus engage in annual latitudinal migrations and that migratory tendency varies with latitude and between sexes. We suggest that this species'' hibernation ecology makes it particularly susceptible to long winters, making migration from the northern extent of the species'' range to more southern hibernacula preferable for some individuals. Fur δD values for some of the northern individuals may indicate an increase in the currently accepted northern range of this species. Sex-biased differences in migration may be the result of differences in reproductive pressures.     

Hormone-induced vocal behavior and midbrain auditory sensitivity in the green treefrog,Hyla cinerea

Summary Twenty four castrated male, 6 intact male, and 11 intact female Hyla cinerea were injected subcutaneously with 25 g arginine-vasotocin (AVT) and induced to call 1 h later in response to the playback of a conspecific mating call. Eighteen castrated males and 8 intact females were implanted 5 mg androgen pellets for 3 weeks prior to the neuropeptide injection. Among castrated males, 6/9 testosterone (T) implanted, 4/9 dihydrotestosterone (DHT) implanted and 2/6 non implanted individuals produced calls after being administered AVT. 5/6 intact non implanted males and 6/8 T intact implanted females also called, and 3 intact non implanted females remained silent after the injection. Evoked calls had a mid-frequency spectral peak at about 1900 Hz which is absent in field-recorded mating calls of this species. Calls of implanted females and castrated non implanted males were shorter than those of castrated implanted and intact non implanted males. Audiograms measured before hormone implants showed dips of enhanced sensitivity at about 0.5, 0.9 and 3.0 kHz in males and females. After AVT injection, thresholds at frequencies within the 0.7–1.5 kHz range were increased in castrated males. Such reduction in sensitivity points to an inhibition of the auditory system during hormone induced vocal activation.Abbreviations AVT arginine-vasotocin - DHT dihydrotestosterone - T testosterone - TS torus semicircularis     

Reproductive biology and endocrine regulation of final oocyte maturation of captive white bass

The ovarian development, and plasma levels of gonadotropin II (GtH II) and sex-steroid hormones at the end of vitellogenesis were examined in captive white bass Morone chrysops. The changes in plasma hormone levels and oocyte morphology associated with gonadotropinreleasing hormone agonist (GnRHa)-induced final oocyte maturation (FOM) were studied. Although plasma 17β-oestradiol (E₂) and oocyte diameter increased, there were no changes in GtH II, testosterone (T), 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) or 17,20β,21-dihydroxy-4-pregnen-3-one (17,20β,21-P) in non-hormone-treated females, and no FOM was observed. Treatment with a sustained-release GnRHa delivery system (GnRHa implant) induced two FOM cycles separated by about 24 h, with the release of approximately equal numbers of eggs in each spawn. Plasma GtH II levels were elevated significantly throughout FOM, reaching a maximum of 9·07 ± 1·55 ng ml^?1 in ovulated fish. Both plasma E₂ and T increased soon after the GnRHa treatment, but E₂ declined in fish undergoing germinal vesicle (GV) migration. Plasma T increased further during FOM (7·55 ± 2·87 ng ml^?1), but declined precipitously at ovulation. A surge in plasma 17,20β-P and 17,20β,21-P (4·11 ± 0·97 ng ml^?1 and 3·10 ± 0·77 ng ml^?1, respectively) was observed in females undergoing GV breakdown (GVBD). Based on the involvement of different sex-steroid hormones, FOM was separated into two stages. Early FOM included lipid-droplet coalescence and GV migration, and was associated with elevations in plasma GtH II and T. Late FOM included GVBD and yolk-globule coalescence, and was associated with elevations in plasma GtH II, 17,20β-P and 17,20β,21-P. The results of this study point to the absence of a surge in plasma GtH II as the missing link in the reproductive axis responsible for the failure of captive white bass to undergo FOM at the end of vitellogenesis. Sustained elevation of plasma GtH II via treatment with a GnRHa implant induced two consecutive spawns with an overall egg production two- to eightfold higher than previously obtained from captive broodstocks, and similar to annual egg production Values reported for wild fish.     

Sex steroids as pheromones in mammals: The exceptional role of estradiol

This article is part of a Special Issue (Chemosignals and Reproduction).Whether from endogenous or exogenous sources, 17β-estradiol (E₂) has very powerful influences over mammalian female reproductive physiology and behavior. Given its highly lipophilic nature and low molecular mass, E₂ readily enters excretions and can be absorbed from exogenous sources via nasal, cutaneous, and other modes of exposure. Indeed, systemic injection of tritiated estradiol (³H-E₂) into a male mouse or bat has been shown to produce significant levels of radioactivity in the reproductive tissues and brain of cohabiting female conspecifics. Bioactive E₂ and other steroids are naturally found in male mouse urine and other excretions, and males actively direct their urine at proximate females. Very low doses of E₂ can mimic the Bruce effect (disruption of peri-implantation pregnancy by novel males), the Vandenbergh effect (early reproductive maturation induced by novel males), and male-induced estrus and ovulation. Males' capacities to induce the Bruce and Vandenbergh effects can both be diminished by manipulations that reduce their urinary E₂. Uterine dynamics during the Bruce and Vandenbergh effects are consistent with the actions of E₂. Collectively, these data demonstrate a critical role of male-sourced E₂ in these major mammalian pheromonal effects.