Chemosignals,hormones and mammalian reproduction

Many mammalian species use chemosignals to coordinate reproduction by altering the physiology and behavior of both sexes. Chemosignals prime reproductive physiology so that individuals become sexually mature and active at times when mating is most probable and suppress it when it is not. Once in reproductive condition, odors produced and deposited by both males and females are used to find and select individuals for mating. The production, dissemination and appropriate responses to these cues are modulated heavily by organizational and activational effects of gonadal sex steroids and thereby intrinsically link chemical communication to the broader reproductive context. Many compounds have been identified as “pheromones” but very few have met the expectations of that term: a unitary, species-typical substance that is both necessary and sufficient for an experience-independent behavioral or physiological response. In contrast, most responses to chemosignals are dependent or heavily modulated by experience, either in adulthood or during development. Mechanistically, chemosignals are perceived by both main and accessory (vomeronasal) olfactory systems with the importance of each system tied strongly to the nature of the stimulus rather than to the response. In the central nervous system, the vast majority of responses to chemosignals are mediated by cortical and medial amygdala connections with hypothalamic and other forebrain structures. Despite the importance of chemosignals in mammals, many details of chemical communication differ even among closely related species and defy clear categorization. Although generating much research and public interest, strong evidence for the existence of a robust chemical communication among humans is lacking.     

Calciotropic hormones during reproduction

This review summarizes the reported effects of the menstrual cycle, pregnancy and lactation on serum concentration of the calciotropic hormones PTH and 1,25(OH)₂D. A midcycle rise in PTH and 1,25(OH)₂D has been observed, but in the majority of studies there was no change in PTH and 1,25(OH)₂D concentrations throughout the menstrual cycle. Both total and free 1,25(OH)₂D levels are increased during pregnancy. The renal 1,25(OH)₂D production is stimulated, and there is some evidence of 1,25(OH)₂D production by decidua/placenta and fetal kidney in vitro; the decidual/placental production should not be overestimated in vivo. The increased renal 1-hydroxylase activity is possibly mediated by estrogens and PTH, although the effect of pregnancy on PTH remains uncertain. Increased serum 1,25(OH)₂D concentrations probably result in a rise of intestinal calcium absorption during pregnancy. There is a postdelivery drop in PTH and 1,25(OH)₂D levels, but they are increased when lactation is prolonged, or in mothers nursing twins. The 1-hydroxylase activity during lactation may be stimulated by PTH, but also by prolactin.     

Can Myxosporean parasites compromise fish and amphibian reproduction?

Research into fish and amphibian reproduction has increased exponentially in recent years owing to the expansion of the aquaculture industry, the need to recover fishery populations, the impact of endocrine disruptors on the aquatic environment and the global decline of amphibian populations. This review focuses on a group of parasites, the Myxozoa, that affect fish and amphibian reproduction. Lists of the myxosporeans that specifically infect gonads are provided. Most of these are parasitic of freshwater hosts, and most amphibian cases are reported from testes. Sex specificity and sex reversal are discussed in relation to gonadal parasitism. The immune response of the fish to the infection is described, and the contribution of the immunoprivilege of gonads to host invasion is emphasized. The pathological effect of these parasites can be significant, especially in aquacultured broodstocks, on some occasions, leading to parasitic castration. Although myxosporean parasites are currently not very frequent in gonads, their impact could increase in the future owing to the transactions in the global market. Their easy release into the aquatic environment with spawning could make their spreading even more feasible. In the absence of commercial drugs or vaccines to treat and prevent these infections, there is an urgent need to develop specific, rapid and reliable diagnostic tools to control and manage animal movements. In addition, much effort is still to be made on deciphering the life cycle of these organisms, their invasion strategies and their immune evasion mechanisms.     

Chemosignals of Stress Influence Social Judgments

Human body odors have important communicative functions regarding genetic identity, immune fitness and general health, but an expanding body of research suggests they can also communicate information about an individual’s emotional state. In the current study, we tested whether axillary odors obtained from women experiencing psychosocial stress could negatively influence personality judgments of warmth and competence made about other women depicted in video scenarios. 44 female donors provided three types of sweat samples: untreated exercise sweat, untreated stress sweat and treated stress sweat. After a ‘washout’ period, a commercial unscented anti-perspirant product was applied to the left axilla only to evaluate whether ‘blocking’ the stress signal would improve the social evaluations. A separate group of male and female evaluators (n = 120) rated the women in the videos while smelling one of the three types of sweat samples. Women in the video scenes were rated as being more stressed by both men and women when smelling the untreated vs. treated stress sweat. For men only, the women in the videos were rated as less confident, trustworthy and competent when smelling both the untreated stress and exercise sweat in contrast to the treated stress sweat. Women’s social judgments were unaffected by sniffing the pads. The results have implications for influencing multiple types of professional and personal social interactions and impression management and extend our understanding of the social communicative function of body odors.     

The effect of beaver (Castor fiber Linnaeus, 1758) activity on amphibian reproduction

The effect of beaver (Castor fiber Linnaeus, 1758) activity on amphibian reproduction was studied in the small river valleys in Novgorod oblast. At sites not subjected to beaver activity, the reproduction rate of amphibians was low. In spring the water in beaver ponds warms up quickly, which attracts amphibians for reproduction. The maximal abundance of tadpoles due to a high reproduction rate was observed in partially drained ponds. However, a high larvae mortality rate was often observed there. Tadpole survival in flooded and empty ponds depends on factors that are not controlled by beavers, such as geomorphology and climate.     

Effects of microgravity on the larval development, metamorphosis and reproduction of the urodele amphibian Pleurodeles waltl

The FERTILE experiment was twice performed onboard the Mir space station during the Cassiopée and Pégase French space missions. The goal was to analyze the effects of microgravity on fertilization and embryonic development, and then on further development on the ground in the amphibian Pleurodeles waltl. The present paper reports development that occurred in the laboratory after landing. Recovered on the ground at the hatching stage, young larvae reared at room temperature underwent metamorphosis and became adults without obvious abnormalities. Of particular interest was the rearing temperature that induced a delayed metamorphosis for animals from the Cassiopée space mission, but not for animals from the Pégase mission. The rate of development and the morphology were analogous in these animals and in ground controls reared in a similar annual period. Analysis of offspring was performed using these animals. Males born in space were first mated with control ground-born females and then with females born in space. The mating gave progeny that developed normally. Depending on the methods used and on the limits of the analyses, the results clearly demonstrated that animals born in space were able to live and reproduce after return to the ground.     

Chemosignals of fear enhance cognitive performance in humans

It is well documented across phyla that animals experiencing stress and fear produce chemical warning signals that can lead to behavioral, endocrinological, and immunological changes in the recipient animals of the same species. Humans distinguish between fear and other emotional chemosignals based on olfactory cues. Here, we study the effect of human fear chemosignals on the speed and accuracy of cognitive performance. In a double-blind experiment, female participants performed a word-association task while smelling one of the three types of olfactory stimuli: fear sweat, neutral sweat, and control odor carrier. We found that the participants exposed to the fear condition performed more accurately and yet with no sacrifice for speed on meaningful word conditions than those under either the neutral or the control condition. At the same time, they performed slower on tasks that contained ambiguous content. Possible factors that could introduce bias, such as individual differences due to anxiety, verbal skills, and perceived qualities of the smells, were ruled out. Our results demonstrate that human fear chemosignals enhance cognitive performances in the recipient. We suggest that this effect originates from learned associations, including greater cautiousness and concomitant changes in cognitive strategies.     

Observations on reproduction,hormones, copulatory behavior,and neonatal mortality in captive Lemur mongoz (Mongoose lemur)

This study examines correlates of reproduction in Lemur mongoz, an endangered prosimian primate with a history of poor captive reproduction. Male testicular growth and regression were quantified via testicular indices (TI). Although TIs could be used to predict male breeding condition, they were not indicators of ability to sire offspring. Serum estradiol (E₂) and progesterone (P) concentrations, along with vaginal cytology, were used to monitor female reproductive cyclicity. E₂ and P profiles showed no abnormalities. An elevation of E₂ with low P, approximately one estrous cycle length (31.4 days) prior to the onset of fertile cycles, was consistent with the phenomenon of ‘pseudoestrus’ observed in other lemur species. The copulatory pattern, consisting of thrusting, multiple intromissions, single or multiple ejaculations, and no copulatory lock, was more complex than expected for an animal with a supposedly monogamous mating system. The preference for natural arboreal substrata during copulation suggests that enclosure furnishings may influence copulatory behavior. A 30% neonatal mortality rate tempered recent success in breeding L. mongoz at the Duke University Primate Center (DUPC). Although infant sex and parity of the mother were not predictive of neonatal mortality, mother's natal status was, with captive-born females having a 67% infant mortality rate, compared with 15% in wild-caught females. Based on these observations, a number of factors, including housing, behavior, and photoperiod, may be relevant to successful captive propagation of L. mongoz. © 1992 Wiley-Liss, Inc.     

Differential regional distribution of gonadotropin-releasing hormones in amphibian (clawed toad, Xenopus laevis) brain

In most vertebrate species two forms of gonadotropin-releasing hormone (GnRH) are present in the brain, and their differential distribution suggests they have different functional roles. The regional distribution and relative concentrations of GnRH molecular forms in the brain of adult clawed toad (Xenopus laevis) were determined using high performance liquid chromatography and radioimmunoassay with a library of region-specific GnRH antisera. Four immunoreactive forms of GnRH were detected: mammalian, hydroxyproline mammalian, chicken II, and an unidetified form of GnRH. Mammalian GnRH was distributed throughout the brain, and hydroxyproline mammalian was present in the forebrain, midbrain (excluding hypothalamus), and hypothalamus. Chicken GnRH II also occurred throughout the brain, but was present in greater amounts in the hindbrain and midbrain (excluding hypothalamus). An unidentified form of GnRH with properties of salmon GnRH was detected in the forebrain. Considering the relative proportions of mammalian GnRH and chicken GnRH II in the major brain areas, the concentration of mammalian GnRH was high in the forebrain, midbrain (excluding hypothalamus), and in particular in the hypothalamus, and very little chicken GnRH II was present in these areas. In the hindbrain, chicken GnRH II predominated and the concentration of chicken GnRH II was highest in the medulla. These findings suggest: (1) mammalian GnRH is the prime regulator of gonadotropin release from the pituitary, and (2) chicken GnRH II has an extrapituitary role.     

Covariation in life-history traits: differential effects of diet on condition, hormones, behavior, and reproduction in genetic finch morphs

The relative contribution of genetic and environmental factors in determining variation in life-history traits is of central interest to evolutionary biologists, but the physiological mechanisms underlying these traits are still poorly understood. Here we experimentally demonstrate opposing effects of nutritional stress on immune function, endocrine physiology, parental care, and reproduction between red and black head-color morphs of the Gouldian finch (Erythrura gouldiae). Although the body condition of black morphs was largely unaffected by diet manipulation, red birds were highly sensitive to dietary changes, exhibiting considerable within-individual changes in condition and immune function. Consequently, nutritionally stressed red birds delayed breeding, produced smaller broods, and reared fewer and lower-quality foster offspring than black morphs. Differences in offspring quality were largely due to morph-specific differences in parental effort: red morphs reduced parental provisioning, whereas black morphs adaptively elevated their provisioning effort to meet the increased nutritional demands of their foster brood. Nutritionally stressed genetic morphs also exhibited divergent glucocorticoid responses. Black morphs showed reduced corticosterone-binding globulin (CBG) concentrations and increased levels of free corticosterone, whereas red morphs exhibited reduced free corticosterone levels and elevated CBG concentrations. These opposing glucocorticoid responses highlight intrinsic differences in endocrine sensitivities and plasticity between genetic morphs, which may underlie the morph-specific differences in condition, behavior, and reproduction and thus ultimately contribute to the evolution and maintenance of color polymorphism.     

Cannabis, cannabinoids and reproduction

In most countries Cannabis is the most widely used illegal drug. Its use during pregnancy in developed nations is estimated to be approximately 10%. Recent evidence suggests that the endogenous cannabinoid system, now consisting of two receptors and multiple endocannabinoid ligands, may also play an important role in the maintenance and regulation of early pregnancy and fertility. The purpose of this review is therefore twofold, to examine the impact that cannabis use may have on fertility and reproduction, and to review the potential role of the endocannabinoid system in hormonal regulation, embryo implantation and maintenance of pregnancy.     

粪便激素水平反映不同出生时期雄性布氏田鼠的繁殖策略

布氏田鼠是我国内蒙古草原的主要害鼠之一,具有明显的季节繁殖特征,不同季节出生个体可能具有不同的繁殖策略,但尚缺乏内分泌证据支持。本研究采用标志重捕法,连续监测大型自然围栏中不同年龄雄性布氏田鼠的繁殖状态和应激水平的季节变化,分析各年龄组雄鼠的繁殖发育策略。结果表明,越冬雄鼠可保持较高的睾丸下降率和睾酮水平至8月初;而部分5月生雄鼠的繁殖期睾酮水平较接近越冬鼠,但8月初已降至年内最低水平,而6月及以后出生雄鼠睾酮始终处于较低水平;这说明越冬鼠的繁殖状态可贯穿繁殖期始终,只有部分5月生雄鼠可能参与当年繁殖,而6月及以后出生雄鼠则不能在当年繁殖。越冬鼠皮质醇水平高于当年鼠,繁殖期高于非繁殖期,这可能是越冬鼠由于繁殖需要而保持较高应激状态,从而造成繁殖盛期后死亡率升高。这些结果说明,不同时期出生的雄性布氏田鼠具有不同的出生后性腺发育模式和繁殖策略,反映出生存与繁殖之间的权衡。     

Structure-function studies of five natural, including catfish and dogfish, gonadotropin-releasing hormones and eight analogs on reproduction in Thai catfish (Clarias macrocephalus).

Five distinct forms of gonadotropin-releasing hormone (GnRH) and their analogs, six of which are newly designed, were used to study reproduction in Thai catfish, Clarias macrocephalus. Determination was made for the percentage of fish that ovulated within 16-18 h; the percentage of eggs fertilized; and the percentage of larva that hatched and survived for 7 days. The results show, firstly, that natural chicken GnRH-II, which is identical with catfish GnRH-II, was significantly more effective at a dose of 300 micrograms/kg than the control injection for the induction of ovulation. Dogfish GnRH at the same dose was also significantly more effective than the control, but was not significantly different from chicken (catfish) GnRH-II for ovulation induction. The novel catfish GnRH-I, mammalian GnRH and salmon GnRH were not effective at 100, 150 or 300 micrograms/kg in Thai catfish. Secondly, 5 of 8 analogs of GnRH at a dose of 20 micrograms/kg resulted in a significantly higher percentage of ovulating fish compared with the control fish. Among these five analogs, the most effective were the two analog forms of chicken GnRH-II (D-Arg6,Pro9 NEt and D-Nal6,Pro9 NEt), followed by the salmon GnRH analog (D-Arg6,Pro9 NEt), a dogfish GnRH analog (D-Arg6,Pro9 NEt) and the mammalian GnRH analog (D-Ala6,Pro9 NEt). Not significantly different from the controls were the two catfish GnRH-I analogs and one of the dogfish (D-Nal6,Pro9 NEt) analogs. The six new analogs had not been previously tested in any animal. Thirdly, the number of fish ovulating was the same whether GnRH was administered in one or two injections.     

Ultraviolet radiation, toxic chemicals and amphibian population declines

Abstract. As part of an overall ‘biodiversity crisis’, many amphibian populations are in decline throughout the world. Numerous factors have contributed to these declines, including habitat destruction, pathogens, increasing ultraviolet (UV) radiation, introduced non‐native species and contaminants. In this paper we review the contribution of increasing UV radiation and environmental contamination to the global decline of amphibian populations. Both UV radiation and environmental contaminants can affect amphibians at all life stages. Exposure to UV radiation and to certain contaminants can kill amphibians and induce sublethal affects in embryos, larvae and adults. Moreover, UV radiation and contaminants may interact with one another synergistically. Synergistic interactions of UV radiation with contaminants can enhance the detrimental effects of the contaminant and UV radiation.