During the past decade, possible advancement in timing of puberty has been reported in the United States. In addition, early pubertal development and an increased incidence of sexual precocity have been noticed in children, primarily girls, migrating for foreign adoption in several Western European countries. These observations are raising the issues of current differences and secular trends in timing of puberty in relation to ethnic, geographical, and socioeconomic background. None of these factors provide an unequivocal explanation for the earlier onset of puberty seen in the United States. In the formerly deprived migrating children, refeeding and catch-up growth may prime maturation. However, precocious puberty is seen also in some nondeprived migrating children. Attention has been paid to the changing milieu after migration, and recently, the possible role of endocrine- disrupting chemicals from the environment has been considered. These observations urge further study of the onset of puberty as a possible sensitive and early marker of the interactions between environmental conditions and genetic susceptibility that can influence physiological and pathological processes.

/pdf/the-timing-of-normal-puberty-and-the-age-limits-of-sexual-4uewdfubug.pdf

The timing of normal puberty and the age limits of sexual precocity: variations around the world, secular trends, and changes after migration

Environmental and social stresses have deleterious effects on reproductive function in vertebrates. Global climate change, human disturbance and endocrine disruption from pollutants are increasingly likely to pose additional stresses that could have a major impact on human society. Nonetheless, some populations of vertebrates (from fish to mammals) are able to temporarily resist environmental and social stresses, and breed successfully. A classical trade-off of reproductive success for potential survival is involved. We define five examples. (i) Aged individuals with minimal future reproductive success that should attempt to breed despite potential acute stressors. (ii) Seasonal breeders when time for actual breeding is so short that acute stress should be resisted in favour of reproductive success. (iii) If both members of a breeding pair provide parental care, then loss of a mate should be compensated for by the remaining individual. (iv) Semelparous species in which there is only one breeding period followed by programmed death. (v) Species where, because of the transience of dominance status in a social group, individuals may only have a short window of opportunity for mating. We suggest four mechanisms underlying resistance of the gonadal axis to stress. (i) Blockade at the central nervous system level, i.e. an individual no longer perceives the perturbation as stressful. (ii) Blockade at the level of the hypothalamic-pituitary-adrenal axis (i.e. failure to increase secretion of glucocorticosteroids). (iii) Blockade at the level of the hypothalamic-pituitary-gonad axis (i.e. resistance of the reproductive system to the actions of glucocorticosteroids). (iv) Compensatory stimulation of the gonadal axis to counteract inhibitory glucocorticosteroid actions. Although these mechanisms are likely genetically determined, their expression may depend upon a complex interaction with environmental factors. Future research will provide valuable information on the biology of stress and how organisms cope. Such mechanisms would be particularly insightful as the spectre of global change continues to unfold.

Reproduction and resistance to stress: When and how

https://sites.oxy.edu/clint/physio/article/thedarwinianconceptofstress.pdf

The Darwinian concept of stress: benefits of allostasis and costs of allostatic load and the trade-offs in health and disease

The functions of estrogen receptors (ERs) in mouse ovary and genital tracts were investigated by generating null mutants for ERalpha (ERalphaKO), ERbeta (ERbetaKO) and both ERs (ERalphabetaKO). All ERalphaKO females are sterile, whereas ERbetaKO females are either infertile or exhibit variable degrees of subfertility. Mast cells present in adult ERalphaKO and ERalphabetaKO ovaries could participate in the generation of hemorrhagic cysts. Folliculogenesis proceeds normally up to the large antral stage in both ERalphaKO and ERbetaKO adults, whereas large antral follicles of ERalpha+/-ERbetaKO and ERalphabetaKO adults are markedly deficient in granulosa cells. Similarly, prematurely developed follicles found in prepubertal ERalphaKO ovaries appear normal, but their ERalphabetaKO counterparts display only few granulosa cell layers. Upon superovulation treatment, all prepubertal ERalphaKO females form numerous preovulatory follicles of which the vast majority do not ovulate. The same treatment fails to elicit the formation of preovulatory follicles in half of the ERbetaKO mice and in all ERalpha+/-/ERbetaKO mice. These and other results reveal a functional redundancy between ERalpha and ERbeta for ovarian folliculogenesis, and strongly suggest that (1) ERbeta plays an important role in mediating the stimulatory effects of estrogens on granulosa cell proliferation, (2) ERalpha is not required for follicle growth under wild type conditions, while it is indispensable for ovulation, and (3) ERalpha is also necessary for interstitial glandular cell development. Our data also indicate that ERbeta exerts some function in ERalphaKO uterus and vagina. ERalphabetaKO granulosa cells localized within degenerating follicles transform into cells displaying junctions that are unique to testicular Sertoli cells. From the distribution pattern of anti-Mullerian hormone (AMH) in ERalphabetaKO ovaries, it is unlikely that an elevated AMH level is the cause of Sertoli cell differentiation. Our results also show that cell proliferation in the prostate and urinary bladder of old ERbetaKO and ERalphabetaKO males is apparently normal.

Effect of single and compound knockouts of estrogen receptors alpha (ERalpha) and beta (ERbeta) on mouse reproductive phenotypes.

Oocyte growth and development is an important issue in fish and fisheries biology. This paper reviews the information available on oocyte growth patterns and the rates and dynamics of oocyte growth in teleosts. In synchronous spawners, the weight of the gonad may represent as much as 40% of the overall body weight of the fish. In asynchronous spawners, the weight of the mature ovary is considerably less than in synchronous ovulators, but the ovary shows a more regular periodicity and may grow repeatedly many times during the breeding season. There is a huge variability in egg size in teleosts, with the largest known measuring up to 8 cm in diameter. Within the limits of variance set by genetic constraints, egg size may vary between populations of the same species. Oocytes in all teleosts undergo the same basic pattern of growth: oogenesis, primary oocyte growth, cortical alveolus stage, vitellogenesis, maturation and ovulation. The mechanisms that control oocyte growth are addressed in this review, albeit that the available information, as in all other vertebrates, is very limited. The main hormones that have been shown to affect ovarian growth are gonadotrophin, thyroid hormones, growth hormone, insulin and insulin-like growth factors. An overview of the determinants of fecundity, with particular reference to oocyte recruitment and atresia, is the focus of the second part of the paper. Genetics and nutrition have major effects on fecundity, and studies so far suggest that the determinants of fecundity usually operate during the early part of gametogenesis. The role of atresia in determining fecundity is less clear. The final part of this review highlights some areas of study that are priorities for research on ovarian development in fish.

Oocyte growth and development in teleosts

Comparative endocrinology is one of the most rapidly developing subdis ciplines within the field of endocrinology, and it is having a significant impact on research at the molecular, cellular, organisma1 and environmental levels. Much of the current ferment in endocrinology is in reproductive endocrinology. The purpose of this volume on hormones and reproduction in fishes, amphibians and reptiles is to summarize our present understandings and to identify important research problems to be addressed in the area of comparative reproductive endocrinology. It was inspired by the gathering at Copper Mountain, Colorado, of eminent endocrine scientists from around the world on the occasion of the Tenth International Symposium on Comparative Endocrinology in July, 1985. While preparing for that meeting, we decided that a special volume on reproductive endocrinology was needed to summarize what is known and to stimulate research in particular directions. Why do we emphasize fishes, amphibians and reptiles? First, knowledge about the reproductive endocrinology of these ectothermic vertebrates can provide a clearer picture of the evolution of reproductive hormones and their effects on target organs. This comparative approach can lead to new theories about the evolution of reproductive control mechanisms. Second, studies concerning the reproductive endocrinology of "lower" vertebrates can result in development of "model systems" for application to studies of birds and mammals. Indeed, information about the patterns of reproductive control in ectothermic vertebrates can tell us which are evolutionarily stable and which are labile."

/pdf/hormones-and-reproduction-in-fishes-amphibians-and-reptiles-41bjvyyu4l.pdf

Hormones and reproduction in fishes, amphibians, and reptiles

Part I: The Adult Female and Male Reproductive Systems Chapter 1: The Brain and Pituitary Gland Chapter 2: The Female Reproductive System Chapter 3: The Menstrual Cycle Chapter 4: The Male Reproductive System Part II: Sex Differentiation and Development Chapter 5: Sexual Differentiation Chapter 6: Puberty Chapter 7: Reproductive Aging Part III: Procreation Chapter 8: The Human Sexual Response Chapter 9: Gamete Transport and Fertilization Chapter 10: Pregnancy Chapter 11: Labor and Birth Chapter 12: The Neonate and the New Parents Part IV: Fertility and Its Control Chapter 13: Human Population Growth and Family Planning Chapter 14: Contraception Chapter 15: Induced Abortion Chapter 16: Infertility Part V: Special Topics in Human Reproductive Biology Chapter 17: Brain Sex Chapter 18: Sexually Transmitted Diseases

Human Reproductive Biology

Summary
1. The incubation patch of birds forms in the areas of the ventrum devoid of contour feathers (apteria) by processes involving defeathering of down, dermal and subdermal hypervascularization, oedema, and hyperplasia of the epidermis and dermal connective tissue. Its formation facilitates the transfer of heat to the eggs and hatched young.

2. In general, the sex that incubates develops a patch; this may be the female, both sexes, or the male, and the species within any one order tend to exhibit a common pattern. In some orders (e.g. Pelecaniformes) no patch develops.

3. The incubation patch begins to form before egg laying in passerine birds and during egg laying in Galliformes. Most of the patch responses in passerines are completed earlier in the reproductive cycle (late egg laying to middle incubation) than in Galliformes (middle incubation to early brooding).

4. In the passerines studied, in which usually only the female develops a patch, oestrogen and prolactin synergize to cause patch development; oestrogen given alone is effective because it synergizes with endogenous prolactin in intact birds. The role of progesterone is unclear, but it seems to mimic the effects of prolactin and also plays a role in the increase in skin sensitivity characteristic of patch development in the canary.

5. In the one galliform studied (California quail), in which both sexes develop a patch, either oestrogen or androgen synergizes with prolactin; oestrogen alone is ineffective in non-breeding quail because of insufficient endogenous prolactin levels. Prolactin alone causes epidermal hyperplasia and vascularization, and progesterone seems mainly to be involved in defeathering. In the starling also both sexes develop a patch, but testosterone plus prolactin is not effective as it is in the quail.

6. In the phalaropes, birds in which only the male develops a patch, androgen and prolactin are the effective synergists in patch development. Thus, there is a correlation between the sex which develops a patch in the wild and the steroid (oestrogen or androgen) which synergizes with prolactin.

7. In the brown-headed cowbird, a parasitic species which neither develops a patch nor incubates, there are no responses to exogenous hormones. The absence of patch development in one sex or in both can be due either to an absence of appropriate hormone levels or to a lack of sensitivity of the skin to hormones.

8. More study is needed of the transfer of heat from the patch area to the eggs or young, including the relationships between patch structure, surface area, surface temperature, type of nest, and the number and size of eggs.

9. Patch formation is affected by and influences behaviour.

10. More research is needed in regard to (I) the natural development and endocrine control of the incubation patch in various orders of birds: (2) the effects of patch formation on behaviour, and vice versa; (3) the mode of action of the hormones in patch formation, that is, whether it is direct or indirect, e.g. through the release of another hormone; (4) the specificity of the ventral skin to hormone administration; (5) the effects of stimulation of the patch by eggs in the nest on prolactin and gonado-trophin secretion; (6) the possible role of other, as yet untested, hormones on patch development; (7) the levels of endogenous hormones in relation to natural patch formation; and (8) possible correlations between the structure of the patch, the chronology of its formation, the clutch size and the condition of the young when hatched in various species.

The incubation patch of birds

Sceloporus aeneus exhibits reproductive bimodality. That is, one taxon (Sceloporus aeneus bicanthalis) is viviparous whereas the other (Sceloporus aeneus aeneus) is oviparous. Morphological differences in luteal and oviductal structure were examined. Oviparous and viviparous females have distinct corpora lutea that form immediately after ovulation and remain active until just prior to oviposition or parturition. Luteal activity is correlated positively with follicular atresia. The oviduct of both subspecies is divided into three distinct morphological regions: an anterior infundibulum, a median uterus, and a posterior vagina. The infundibulum and vagina of females exhibiting either parity type are similar, whereas distinct differences in utering morphology are apparent. Primarily, these differences include the loss of uterine glands and a reduction in epithelial cell height in the viviparous form. Moreover, viviparous females possess a simple but well-developed chorioallantoic placenta and a simple choriovitelline placenta. Chorioallantoic placentation is associated with a significant increase in uterine vascularity, indicating a role in gas and/or water exchange. The evolution of viviparity and placentation are discussed in relation to these observations.

Ovarian, oviductal, and placental morphology of the reproductively bimodal lizard, Sceloporus aeneus

We compared modes of reproduction in the lizard genus Sceloporus with ele- vation, latitude, environmental moisture, habits, and body size. Viviparous species of Sceloporus more commonly are found at high elevation than at low elevation, and tend to exhibit arboreal or saxicolous habits. Our findings suggest the following hypothesis: Within oviparous species of Sceloporus, animals exhibiting egg retention have a selective advantage over conspecifics in the cold environments of high elevation or latitude. Egg retention leads to ovoviviparity in which eggs hatch in utero. Once ovoviviparity has evolved, the placenta evolves primarily as an ad- aptation to supply oxygen to the developing embryo. Viviparous forms then can assume an arboreal or saxicolous habit as an anti-predatory and/or thermoregulatory adaptation. Finally, viviparity evolves as an irreversible trait. Subsequent radiation of the viviparous forms produces species that can live in environments not originally a factor in the evolution of the viviparous mode of reproduction.

Richard E. Jones

Papers

Hormones and reproduction in fishes, amphibians, and reptiles

Human Reproductive Biology

The incubation patch of birds

Ovarian, oviductal, and placental morphology of the reproductively bimodal lizard, Sceloporus aeneus

Evolution of viviparity in the lizard genus sceloporus