Sex differences in adrenal function in the lizard Cnemidophorus sexlineatus: I. Seasonal variation in the field.

In order to document sex differences in adrenal function and how this relates to gonadal function during the period of seasonal activity, blood samples from male and female six-lined racerunners, Cnemidophorus sexlineatus, were taken immediately after capture in the field for determination of plasma corticosterone and gonadal steroid concentrations. Plasma testosterone and dihydrotestosterone levels for males, and 17 beta-estradiol and progesterone levels for females, were measured. Trends in the concentration of plasma corticosterone differed significantly between males and females. In males the highest concentrations of corticosterone were measured in late spring and the lowest concentrations were measured in late summer. Whereas half of the variation in corticosterone levels among males could be explained as seasonal change, less than 1% of the variation among females could be explained as seasonal change. In males plasma corticosterone and androgens exhibited similar seasonal decreases. Corticosterone levels for females were not correlated with progesterone or 17 beta-estradiol levels. Sex differences in seasonal variation in plasma corticosterone concentrations suggest that corticosterone may be involved in the different reproductive strategies and energy requirements of males and females during the seasonal period of activity.     

Hormones and mating system affect sex and species differences in immune function among vertebrates

Males generally exhibit reduced immune responses as well as increased intensity and prevalence of infections compared to female conspecifics. Physiologically, these sex differences may reflect the immunosuppressive effects of androgens. In addition to suppressing immune function, androgens maintain several characteristics important for reproductive success. Thus, a dynamic relationship is assumed to exist among hormones, secondary sex traits, and the immune system. Ultimately, the extent to which this relationship exists may be related to the mating system. Because polygynous males generally have higher circulating testosterone concentrations and rely more heavily on testosterone-dependent traits for reproductive success than monogamous males, sex differences in immune function are hypothesised to be more pronounced among polygynous as compared to monogamous species. Additionally, if secondary sex traits are used to advertise infection status, then females should be able to use the condition of male secondary sex traits to discern the immune/infection status of males during mate selection. The purpose of this review is to survey current studies that examine both the proximate mechanisms and ultimate function of variation in immune function and susceptibility to infection and determine whether immunological variation influences mate preference and possibly reproductive success.     

Functional and morphological diversity of sperm in Drosophila

Unlike mammals, where the males produce huge quantities of tiny spermatozoa, insects, and Drosophila in particular, exhibit a wide range of reproductive strategies. Sperm gigantism in Drosophila deviates from the rules that normally govern anisogamy, i.e. differences in the size and quantity of male and female gametes. Sperm gigantism has driven anatomical, physiological and cytological adaptations that affect the correlated evolution of the male and female reproductive systems, and has led to the evolution of a new structure, the roller, located between the testis and the seminal vesicle, and to sperm coiling to form pellets. The diversification of sperm strategy is investigated in the light of sexual selection processes that occur in the female genital tract after copulation. These processes, which bias paternity, result from interactions either between spermatozoa from different males, or between the spermatozoa and the environment within the female reproductive tract. In Drosophila, increased sperm size does not confer any reproductive advantage on the male. The evolution of sperm gigantism does not seem to be attributable to competition between spermatozoa from different males, as has been shown to occur in some vertebrate species. Alternative mechanisms, such as interactions between spermatozoa and the female reproductive system, are therefore currently viewed as being more likely explanations. In particular, the impact of sperm size on female reproductive physiology is being investigated to find out whether having large spermatozoa increases the likelihood of male reproductive success. Correlated adaptations of the spermatozoa and female storage organs also seem to be a major factor in determining sperm success, and their role in male-female conflicts is discussed briefly.     

Regulation of male fertility by the opioid system

Endogenous opioid peptides are substances involved in cell communication. They are present in various organs and tissues of the male and female reproductive tract, suggesting that they may regulate some of the processes involved in reproductive function. In fact, the opioid system that operates as a multi-messenger system can participate in the regulation of reproductive physiology at multiple levels, for example, at the levels of the central nervous system, at the testes level and at sperm level. A better understanding of the implication of the opioid system in reproductive processes may contribute to clarifying the etiology of many cases of infertility and the effect of opiate abuse on fertility. Indeed, a novel biochemical tool for the diagnosis and treatment of male infertility could be based upon components of the opioid system. The presence of the opioid system in sperm cells also represents a novel opportunity for reproductive management, for either enhancing the probability of fertilization or reducing it through the development of novel targeted contraceptives.     

Hypothyroidism in reproductively inhibited prairie deer mice (Peromyscus maniculatus bairdi) from laboratory populations

Several thyroid function parameters were compared between reproductively inhibited prairie deer mice of both sexes taken from laboratory populations and corresponding reproductively capable controls. The results of these experiments indicated the following: 1) prairie deer mice females had a statistically significant daily variation in mean serum thyroxine concentration and males displayed a similar trend; 2) total serum thyroxine and triiodothyronine were significantly lower in both male and female reproductively inhibited population animals compared with reproductively capable controls; 3) several morphometric characteristics of the thyroid of male and female population prairie deer mice were significantly different from that of control males and females, suggesting functional hypothyroidism in both sexes; 4) thyroid histology of male population deer mice was different from that of female population animals. In males, the data suggested that thyroid-stimulating hormone (TSH) stimulation was deficient due to some undetermined secondary hypothyroidism. In females, reduced serum thyroxine and triiodothyronine concentrations were observed due to primary hypothyroidism of unknown origin. The interrelationship between thyroid and adrenal function is discussed here and it is concluded that each of the systems may contribute to the observed reproductive inhibition. In particular, it was noted that the mechanism of response between population males and females may be quite different. No conclusive data are available to suggest whether one or the other system is the primary controller of the reproductive inhibition.     

Endocrine Monitoring of Wild Dominant and Subordinate Female Leontopithecus rosalia

In captive callitrichid primates, female reproductive function tends to vary with social status. However, little is known about the interplay between these factors in wild groups. We report observations on normative ovarian function in dominant and subordinate female golden lion tamarins (Leontopithecus rosalia) living in wild groups. We monitored ovarian status by measuring, via enzyme immunoassay, concentrations of excreted pregnanediol glucuronide (PdG) and estrone conjugates (E₁C) in fecal samples collected noninvasively from individuals in social groups in the Poço das Antas Biological Reserve, Rio de Janeiro State, Brazil. Dominant breeding females demonstrated steroid levels similar to those previously reported for wild cotton-top tamarin females, with statistically significant rises during pregnancy. The duration of elevation of fecal steroids in breeding females was ca. 4 mo, which corresponds with estimates of gestation from captive studies. Low steroid concentrations from December to June suggest a seasonally-related period of infertility in female golden lion tamarins. Dominant and subordinate females demonstrated several differences in endocrine function. In general, younger females living in intact natal family groups showed no evidence of ovarian cyclicity. We noted endocrine profiles consistent with ovulation and subsequent pregnancy for behaviorally subordinate females living in groups with unrelated males or in which a reversal in female dominance status occurred. Results suggest that in addition to changes in female reproductive endocrinology associated with puberty, the regulation of reproduction in females in wild callitrichid groups can be sensitive to status and relatedness to breeding males.     

赤腹松鼠血清性激素水平的季节差异

正季节性繁殖是动物适应环境的具体表现,也是动物维持其种群发展的重要策略。生殖激素和动物的繁殖活动关系密切,协调实现繁殖后代的机能(赖平等,2012),如配子的发生、成熟与排出及受精、妊娠、分娩与泌乳等性行为活动。例如雄性甘肃鼢鼠(Myospalax cansus)血清中睾酮(程志兴,2009)和黄山短尾猴(Macaca thibetana)血清中孕酮含量(夏东坡,2007)在交配期间显著升高,     

Effects of prenatal treatment with antiandrogens on luteinizing hormone secretion and sex steroid concentrations in adult spotted hyenas,Crocuta crocuta

Prenatal androgen treatment can alter LH secretion in female offspring, often with adverse effects on ovulatory function. However, female spotted hyenas (Crocuta crocuta), renowned for their highly masculinized genitalia, are naturally exposed to high androgen levels in utero. To determine whether LH secretion in spotted hyenas is affected by prenatal androgens, we treated pregnant hyenas with antiandrogens (flutamide and finasteride). Later, adult offspring of the antiandrogen-treated (AA) mothers underwent a GnRH challenge to identify sex differences in the LH response and to assess the effects of prenatal antiandrogen treatment. We further considered the effects of blocking prenatal androgens on plasma sex steroid concentrations. To account for potential differences in the reproductive state of females, we suppressed endogenous hormone levels with a long-acting GnRH agonist (GnRHa) and then measured plasma androgens after an hCG challenge. Plasma concentrations of LH were sexually dimorphic in spotted hyenas, with females displaying higher levels than males. Prenatal antiandrogen treatment also significantly altered the LH response to GnRH. Plasma estradiol concentration was higher in AA-females, whereas testosterone and androstenedione levels tended to be lower. This trend toward lower androgen levels disappeared after GnRHa suppression and hCG challenge. In males, prenatal antiandrogen treatment had long-lasting effects on circulating androgens: AA-males had lower T levels than control males. The sex differences and effects of prenatal antiandrogens on LH secretion suggest that the anterior pituitary gland of the female spotted hyena is partially masculinized by the high androgen levels that normally occur during development, without adverse effects on ovulatory function.     

Androgens and Immune Function in Male Alternative Reproductive Morphotypes of the Peacock Blenny Salaria pavo

Species with alternative reproductive tactics offer the opportunity to analyse how behavioural and morphological traits are tuned to produce successfully competing phenotypes within one sex. In the teleost fish Salaria pavo , alternative reproductive tactics are sequential. The older ornamented males compete for access to females by guarding a cavity to which they attract females to spawn. Ornamented males that are found without a nest are called 'floaters'. Younger mature males which are too small to compete with nest-holders attempt to 'sneak' as female mimics into successful nests and release their sperm to fertilize freshly spawned eggs. The alternative tactics in S. pavo are associated with different levels of the androgens testosterone and 11-ketotestosterone, which have been found to suppress immune function in several teleost fish. A field study was carried out to analyse the relationship between these reproductive tactics, androgens and blood levels of lymphocytes as a monitoring method of immune function. We expected highest investment in the immune system in sneakers because these have the lowest androgen levels and functionally because investing in self-maintenance increases their future prospect to switch tactic and to reproduce as a nest-holder. Indeed, the relative count of lymphocytes correlated negatively with body size and thus was highest in sneakers and lowest in nest-holders. In concordance, 11-ketotestosterone and testosterone levels were found to be higher in floaters and nest-holders than in sneakers. However, no correlation was found between individual levels of testosterone or 11-ketotestosterone and lymphocytes. Thus, a trade-off between reproductive traits associated with high androgen levels and immunocompetence might exist at the level of alternative tactics but this might not be explained by acute immunosuppressive effects of circulating androgens.     

Circulating LH levels and the response to exogenous GnRH in the common mole-rat: implications for reproductive regulation in this social, seasonal breeding species

The effects of breeding season and reproductive status on male and female reproduction were investigated in the common mole-rat, Cryptomys hottentotus hottentotus, a cooperatively breeding rodent which exhibits a unique combination of seasonal breeding and a reproductive division of labor. Pituitary function was examined by measuring the luteinizing hormone (LH) responses to single doses of 2 microg exogenous gonadotrophin-releasing hormone (GnRH) and physiological saline in 69 males and 58 females from 35 wild caught colonies. Neither males nor females exhibited any apparent manifestation of season on basal LH concentrations or on pituitary sensitivity to stimulation by exogenous GnRH. The continuance of reproductive function during the nonbreeding period is essential in common mole-rat males and females, as this period coincides with the period of maximal dispersal opportunity in the winter rainfall area they inhabit. Normal circulating levels of reproductive hormones in dispersing animals may aid intersexual recognition, assist pairbond formation, and thus prime animals for independent reproduction. Circulating basal concentrations of LH as well as LH levels measured in response to a single exogenous GnRH challenge were not significantly different between the reproductive and non-reproductive groups of either sex, suggest the absence of a physiologically well-defined suppression of reproduction in subordinate common mole-rats.     

Perinatal 17α-ethinylestradiol exposure affects formalin-induced responses in middle-aged male (but not female) rats

17α-Ethinylestradiol (EE), the main component of the contraceptive pill, is a synthetic estrogen found in rivers of the United States and Europe as an environmental contaminant. It is one of the most studied xenoestrogens due to its possible effect on the reproductive system. In the present study we evaluated the modulation of pain responses induced by formalin injection (licking, flexing, paw-jerk) in 8-month-old male and female offspring of female rats treated with two different doses of EE (4 ng/kg/day or 400 ng/kg/day) during pregnancy and lactation. Spontaneous behaviors and gonadal hormone levels were also determined. Both concentrations of EE induced an increase of pain behaviors in males only, i.e. higher flexing and licking of the formalin-injected paw than in OIL-exposed rats, during the second, inflammatory, phase of the formalin test. Grooming duration was increased by EE exposure in both males and females. Prenatal EE exposure (both concentrations) decreased estradiol plasma levels in the formalin-injected females but not in the males. These results underline the possibility that exposure to an environmental contaminant during the critical period of development can affect neural processes (such as those involved in pain modulation) during adulthood, indicating long-term changes in brain circuitry. However, such changes may be different in males and females.     

Optical coherence tomography for dynamic investigation of mammalian reproductive processes

The biological events associated with mammalian reproductive processes are highly dynamic and tightly regulated by molecular, genetic, and biomechanical factors. Implementation of live imaging in reproductive research is vital for the advancement of our understanding of normal reproductive physiology and for improving the management of reproductive disorders. Optical coherence tomography (OCT) is emerging as a promising tool for dynamic volumetric imaging of various reproductive processes in mice and other animal models. In this review, we summarize recent studies employing OCT-based approaches toward the investigation of reproductive processes in both, males and females. We describe how OCT can be applied to study structural features of the male reproductive system and sperm transport through the male reproductive tract. We review OCT applications for in vitro and dynamic in vivo imaging of the female reproductive system, staging and tracking of oocytes and embryos, and investigations of the oocyte/embryo transport through the oviduct. We describe how the functional OCT approach can be applied to the analysis of cilia dynamics within the male and female reproductive systems. We also discuss the areas of research, where OCT could find potential applications to progress our understanding of normal reproductive physiology and reproductive disorders.     

Colony structure and parentage in wild colonies of co-operatively breeding Damaraland mole-rats suggest incest avoidance alone may not maintain reproductive skew

Colonies of co-operatively breeding African mole-rats have traditionally been thought to be composed of a single breeding female, one or two breeding males, and their offspring. In the naked mole-rat (Heterocephalus glaber), the occurrence of facultative inbreeding means incest avoidance cannot prevent reproduction in subordinate group members, and physiological suppression of reproductive function by the breeding female occurs in both sexes. In contrast, previous studies of captive colonies of the Damaraland mole-rat (Cryptomys damarensis) suggest that breeding within a colony is restricted to a single breeding pair, simply because all other colony members are highly related (first- or second-order relatives) and this species is an obligate outbreeder. Using microsatellite markers, we investigated parentage and colony composition in 18 wild Damaraland mole-rat colonies to determine whether inbreeding avoidance alone can explain the high levels of reproductive skew in this species. Multiple and unidentified paternity was widespread within colonies and immigrants of both sexes were regularly identified. Unrelated, opposite-sex nonbreeders were found coexisting in two colonies. These results suggest that, in the wild, conditions exist where nonreproductive females can come into contact with unrelated males, even when they do not disperse from their natal colony. Inbreeding avoidance alone is therefore insufficient to maintain the high levels of reproductive skew identified in this species suggesting that the breeding female somehow suppresses the reproductive function in nonbreeding females.     

Social regulation of plasma estradiol concentration in a female anuran

The behavior of an individual within a social aggregation profoundly influences behavior and physiology of other animals within the aggregation in such a way that these social interactions can enhance reproductive success, survival and fitness. This phenomenon is particularly important during the breeding season when males and female must synchronize their reproductive efforts. We examined whether exposure to conspecific social cues can elevate sex steroid levels, specifically estradiol and androgens, in female túngara frogs (Physalaemus pustulosus). We compared plasma estradiol and androgen concentrations in wild-caught females before and after exposure to either natural mate choruses or random tones. After exposure to mate choruses for 10 consecutive nights, estradiol concentrations were significantly elevated whereas there was no significant elevation in estradiol concentrations in the group of females exposed to random tones for 10 nights. Plasma androgen concentrations were not significantly changed after exposure to either natural mate choruses or random tones for 10 consecutive nights. Social modulation of estradiol concentrations may be important in maintaining a female's reproductive state while males are chorusing. To our knowledge, this is the first study to demonstrate social regulation of estradiol concentration in female anurans.     

Female reproductive fluid concentrations affect sperm performance of alternative male phenotypes in an external fertilizer

There is growing evidence that the female reproductive fluid (FRF) plays an important role in cryptic female choice through its differential effect on the performance of sperm from different males. In a natural spawning event, the male(s) may release ejaculate closer or further away from the spawning female. If the relative spatial proximity of competing males reflects the female pre-mating preference towards those males, then favoured males will encounter higher concentrations of FRF than unpreferred males. Despite this being a common situation in many external fertilizers, whether different concentrations of FRF can differentially influence the sperm performance of distinct male phenotypes (favoured and unfavoured by the female) remains to be elucidated. Here, we tested this hypothesis using the grass goby (Zosterisessor ophiocephalus), a fish with distinct territorial-sneaker reproductive tactics and female pre-mating preference towards territorial males, that consequently mate in an advantaged position and whose sperm experience higher concentrations of FRF. Our findings revealed a differential concentration-dependent effect of FRF over sneaker and territorial sperm motility only at low concentrations (i.e. at the distance where sneakers typically ejaculate), with increasing FRF concentrations (i.e. close to the eggs) similarly boosting the sperm performance of both sneaker and territorial males. The ability to release sperm close to the eggs is a prerogative of territorials, but FRF can likewise advantage the sperm of those sneakers that are able to get closer, allowing flexibility in the direction of female post-mating choice.     

Sexual conflict and female immune suppression in the cricket, Allonemobious socius

In many animal systems, females exhibit a localized immune response to insemination that helps defend against sexually transmitted disease. However, this response may also kill sperm, reducing a male's reproductive potential. If males could suppress this response, they may be able to increase their sperm's representation in the female's reproductive tract, thereby increasing their fitness. Here we address the hypothesis that, under conditions of sperm competition, males interfere with female immunity. To test our hypothesis, we manipulated levels of female mating frequency (single vs. multiply mated) and seminal diversity (monandrous vs. polyandrous) in the cricket, Allonemobius socius and measured female immune response. As mating frequency increased, female hemocyte load decreased, indicating a general reproductive cost. As seminal diversity increased, phenoloxidase (PO) activity (in vitro measure of 'potential' macroparasitic defense) increased and encapsulation ability (in vivo measure of 'realized' macroparasitic defense) decreased in polyandrous females. These results suggest that males may manipulate female immunity by interrupting the pro-PO cascade, which begins with the activation of PO and ends in the encapsulation of invading foreign bodies. In other words, female immune function may serve as a battleground over which a sexual conflict is fought.     

Hormonal and behavioral changes at puberty in the squirrel monkey

Developmental changes in the reproductive behavior and physiology of 9 male and 15 female juvenile squirrel monkeys were evaluated in a 20-month study. Plasma levels of gonadal steroids remained relatively low for this species until most animals reached puberty between 2.5 and 3 years of age. Longitudinal assessment of plasma progesterone levels indicated that the onset of ovarian cycles tended to be synchronized between females although the 5 heaviest females began to cycle earlier than the rest. The heavier females reached puberty at a time which was appropriate to their birth in the wild, whereas most of the remaining females conceived 6 months later during a second period of reproductive activity that coincided with the laboratory mating season. Pubescent males underwent their first seasonal elevation in plasma testosterone levels during the second period and its onset was synchronized across all males. Thus, even in the absence of adults, pubertal processes in the squirrel monkey were strongly influenced by the seasonal breeding pattern. In addition, behavioral observations revealed that social maturation closely parallels reproductive ability in females, whereas males enter a protracted subadult stage after puberty.     

A TEST FOR ENVIRONMENTAL EFFECTS ON BEHAVIORAL ISOLATION IN TWO SPECIES OF KILLIFISH

Behavioral isolation is a common and potent mechanism of reproductive isolation. Determining the extent to which behavioral isolation varies with environmental conditions is critical to understanding speciation and the maintenance of species boundaries. Here, we tested the effect of salinity on behavioral isolation (female species recognition, male–male competition, and male species recognition) between two closely related killifish (Lucania goodei and L. parva) that differ in salinity tolerance. We performed no‐choice assays and behavioral trials where males could compete and court females in fresh water (0 ppt) and brackish water (15 ppt). We found high levels of behavioral isolation that did not vary as a function of salinity. In behavioral trials, male species recognition of females was strong and asymmetric between the two species. Lucania goodei males preferred conspecifics and rarely courted or mated with L. parva females. Lucania parva males preferred conspecifics but readily courted and mated with L. goodei females. This asymmetry matches previously documented asymmetries in hybrid offspring fitness. Crosses between L. parva males and L. goodei females produce fully viable/fertile hybrids, but crosses between L. goodei males and L. parva females produce males with reduced fertility. Hence, behavioral isolation may have evolved in part due to reinforcement.