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PubMed1996

Establishment probability in fluctuating environments: a branching process model.

We study the establishment probability of invaders in stochastically fluctuating environments and the related issue of extinction probability of small populations in such environments, by means of an inhomogeneous branching process model. In the model it is assumed that individuals reproduce asexually during discrete reproduction periods. Within each period, individuals have (independent) Poisson distributed numbers of offspring. The expected numbers of offspring per individual are independently identically distributed over the periods. It is shown that the establishment probability of an invader varies over the reproduction periods according to a stable distribution. We give a method for simulating the establishment probabilities and approximations for the expected establishment probability. Furthermore, we show that, due to the stochasticity of the establishment success over different periods, the expected success of sequential invasions is larger then that of simultaneous invasions and we study the effects of environmental fluctuations on the extinction probability of small populations and metapopulations. The results can easily be generalized to other offspring distributions than the Poisson.

Demography↗
PubMed1995

Relation of early menarche to high bone mineral density.

The study of background factors in individuals with high bone mineral density (BMD) may provide useful information in the prevention of osteoporosis. We investigated the relationship of reproductive factors to BMD. In 519 female volunteers (327 postmenopausal and 192 premenopausal women) ranging in age from 21 to 74 (mean 52.3 +/- 11.8) years, spinal BMD values were obtained using both quantitative computed tomography and dual x-ray absorptiometry. The z score was calculated from the mean BMD in each 5-year age group, and high BMD and low BMD was defined as BMD with z score > + 1.5 and < -1.5, respectively. Normal BMD was defined as BMD within the range - 1.0 < z score < +1.0. Long reproductive period, early menarche, and late menopause were associated with high BMD. Among these, the reproductive period showed the strongest association with BMD. In postmenopausal women, early menopause had a significant relationship with low BMD, and early menarche also had some relation to high BMD. In premenopausal women, there was a significant relationship between early menarche and high BMD. The age at menarche may have a strong association with peak bone mass, as suggested by the positive correlation of early menarche with high BMD observed in this study. It is considered important to prevent risk factors that disturb the beginning of menstruation in adolescent girls.

Absorptiometry, Photon↗
PubMed2001

Temporal and quantitative changes in sexual reproductive cycling of the cladoceran Daphnia magna by a juvenile hormone analog.

Cyclic parthenogens, such as the cladoceran, Daphnia magna, utilize both asexual (parthenogenetic) and sexual reproduction in order to maximize population fitness in variable environments. Parthenogenetic reproduction is the default strategy among D. magna, while various environmental cues trigger cycles of sexual reproduction. Experiments were conducted with the juvenile hormone analog methoprene to test the hypothesis that members of the insect juvenile hormone/vertebrate retinoic acid family of transcription factors are involved in the regulation of sexual reproduction in daphnids. Neither methoprene, food reduction, or crowding independently stimulated entry into the sexual reproductive phase of the daphnids. However, the combination of food deprivation and crowding stimulated entry into the sexual reproductive phase characterized by an initial high production of males and the subsequent intermittent production of haploid egg-containing ephippia. Exposure to 160 nM methoprene along with food deprivation and crowding caused a significant reduction in the percentage of males produced during the early phase of the sexual cycle and significantly increased the percentage of males produced during the later stages of the cycle. Methoprene concentrations as low as 6.4 nM significantly reduced the number of resting eggs produced and proportionately increased the production of parthenogenetically-produced neonates. These experiments demonstrate that methoprene uncouples the coordinate production of males and resting eggs during the sexual reproductive period of D. magna. Methoprene stimulates male offspring production and defers their production to latter stages of the sexual reproductive period, while inhibiting the production of resting eggs and promoting the continuance of parthenogenetic reproduction. J. Exp. Zool. 290:148-155, 2001.

Animals↗
PubMed2004

Effects of methoxychlor exposure during perinatal period on reproductive function after maturation in rats.

Methoxychlor (MXC) is a non-steroidal pesticide that is known to possess estrogenic activity, and therefore may be potentially hazardous to the development and/or reproduction. The present study assessed the effects of perinatal exposure to MXC on reproductive function after maturation in both male and female rats. Pregnant rats were fed a phytoestrogen-free diet containing different doses of MXC (24, 240, and 1200 ppm) from day 15 of gestation to day 10 after parturition, and reproductive functions of offspring were examined after maturation. In males, MXC exposure during the perinatal period decreased serum LH and FSH, but not testosterone levels, but it did not affect copulatory behavior. In females, MXC exposure prolonged the days exhibiting cornified vaginal smears during the estrous cycle. In addition, both the lordosis reflex and preovulatory LH surge on the presumptive proestrous evening were suppressed in MXC-exposed females. These results suggest that perinatal exposure to MXC exerts permanent effects on several aspects of the reproductive function in both male and female rats.

Animals↗
PubMed1994

Testicular melanin pigments and the gonadal cycle in a tropical wild passerine bird, Dicrurus adsimillis (passeriformes, dicruridae).

Seasonal variation of the coloration of the testes due to the presence of melanin pigments was observed in a wild passerine bird Dicrurus adsimillis. The proportion of melanin in the testes is highest in the recrudescence period, when the lipid content is moderate and cholesterol is present in the tissue in trace amounts. In the reproductive period, when lipids are depleted, the melanin content is very low; in this stage, cholesterol is stored in the tissue in large amounts. During the post-reproductive period, melanin pigment and lipids both fall almost to zero level and only traces of cholesterol are to be found. In the recrudescence phase, the amount of all three (i.e. melanin pigment, tissue lipids and cholesterol) rapidly increases. The probable correlation between melanogenesis in testicular tissue and hormones and their lipoid precursors is discussed.

Animals↗
PubMed2002

Where the boys are not: a brief overview of male preventive health.

Excess morbidity and premature mortality in US males is caused, in part, by lack of male participation in preventive health behaviors. Unlike women, who routinely access the health care system for periodic reproductive exams, men between the ages of 15 and 50 rarely seek preventive care services. A chart survey of a sample of female reproductive exams was undertaken to investigate the types of health care services these exams provide. Results indicated that a periodic female reproductive exam often encompasses many elements of a comprehensive history and physical exam, thus serving as an ideal preventive health vehicle, and is reimbursed as such by non-Medicare payers using preventive health codes. In most cases, reproductive issues were a minor portion of the female reproductive exam. It is speculated that males would also benefit from similar periodic, gender-appropriate preventive health exams. Like periodic reproductive exams for women, these "well male exams" would serve as abbreviated comprehensive history and physical exams, and would be reimbursed using the same preventive health codes. A list of age-appropriate preventive health interventions for men is suggested.

Adolescent↗
PubMed2004

The role of calcium in the nuclear maturation of Bufo arenarum oocytes.

In Bufo arenarum, progesterone is the physiological maturation inducer. However, in this species, oocytes reinitiate meiosis with no need of an exogenous hormonal stimulus when deprived of their enveloping cell, a phenomenon called spontaneous maturation. We demonstrated that in Bufo arenarum spontaneous maturation occurs only in oocytes obtained during the reproductive period, which can be considered competent to mature spontaneously, in contrast to those in the non-reproductive period, which are incompetent. Interestingly, full-grown Bufo arenarum oocytes always respond to progesterone regardless of the season in which they are obtained. There is a general consensus that both a transient increase in intracellular calcium and a decrease in cAMP-dependent protein kinase activity are the first steps in the mechanisms by which progesterone induces maturation in amphibians. In the present work we analysed the role of calcium in the spontaneous and progesterone-induced maturation of Bufo arenarum oocytes. Results demonstrated that the absence of calcium in the incubation medium or the prevention of Ca(2+) influx by channel blockers such as CdCl2 or NiCl2 did not prevent meiosis reinitiation in either type of maturation. The inhibition of the Ca(2+)-calmodulin complex in no case affected the maturation of the treated oocytes. However, when the oocytes were deprived of calcium by incubation in Ca(2+)-free AR + A23187, meiosis resumption was inhibited. In brief, we demonstrated that in Bufo arenarum the reinitiation of meiosis is a process independent of extracellular calcium at any period of the year and that oocytes require adequate levels of intracellular calcium for germinal vesicle breakdown to occur.

Animals↗
PubMed1981

[Gonadal endocrine function indicators during initial stages of postnatal ontogenesis of the female sable].

By means of radioimmunoassay, 17 beta-estradiol-, androgen- (testosterone and dihydrotestosterone) and progesterone contents were determined in the peripheral blood of the female sables, aged 2 to 27 months, during postnatal ontogenesis initial stage. Under the action of seasonal factors steroid level was sharply decreased in the animals of the all ages within the autumnal period, whereas the gonadal function activation lowered over a period of February and March, when "the spring animation" of wild stables is seen. An increase in the sex hormone level was more pronounced in females over one year old. The compared concentrations of hormones, studied in the 5-months' females (the growth stopping). 14 to 17-months' animals (the 1st year reproductive period) and 27-months' stables (the 2nd year reproductive period) were close to those of 17 beta-estradiol and progesterone contents in fertile animals. It is suggested that the sexual system of the 5-months' females is ready for the reproductive processes but their secretory activity is sharply reduced, probably under the seasonal factor influence.

Aging↗
PubMed2005

Localization of acid phosphatase activity in the testis of two teleostean species (Oreochromis niloticus and Odonthestes perugiae).

Acid phosphatase (AcP) activity was investigated in the testes of two species of teleosts in two seasons: summer and winter. AcP activity was detected in Sertoli cells from tilapia (Oreochromis niloticus) only during the nonreproductive period of its annual cycle, corresponding to the winter months. In kingfish (Odonthestes perugiae), the enzymatic reaction was identified during the non-reproductive period (summer) in epithelial cells of the efferent ducts but not in Sertoli cells. These data suggest that the enzyme is involved in the absorption of residual spermatid cytoplasm and as well as in the removal of spermatozoa remaining after the reproductive period. In kingfish, this heterophagous function is carried out by the efferent duct cells and not by Sertoli cells.

Acid Phosphatase↗
PubMed2006

Age, reproduction and fecundity of the spined loach Cobitis taenia L. (Pisces, Cobitidae) from Lake Klawój (Poland).

This is the first study concerning the features of the reproduction process of the karyologically identified spined loach C. taenia (2n=48). The histology of 71 ovaries, and gonadosomatic index (GSI) of karyologically identified spined loach Cobitis taenia L. from Lake Klawój (Northern Poland) were examined. The absolute and relative fecundity of 25 females was estimated by gravimetric method. The age of fish was determined according to the annual increments of otholits. The spawning of C. taenia from Lake Klawój took place from May to July, at a water temperature exceeding 18.5 degrees C. The GSI values at the beginning of the reproduction period ranged from 7 to 19%. The average absolute fecundity of females was 2078 eggs, with the number ranging from 869 to 3371 eggs. High individual variability in the gonad histology and the GSI values during the reproductive period was observed. Such variability could be the result of beginning the reproduction process in the fish at various times and, probably, due to the various numbers of batches laid and various numbers of eggs per batch.

Age Factors↗
PubMed2005

[Physiological significance of calcitonin in fish].

The physiological role of calcitonin (CT) in fish has been partially elucidated. In teleosts, CT did not affect the calcium (Ca) and phosphate contents in bone and scales. In an experiment using Ca(45), CT did not show any change in the Ca flux of the scales. To examine the effect of CT on osteoclasts in teleosts, therefore, we developed a new culture system using goldfish scales. This system can detect osteoclastic and osteoblastic activities very sensitively using tartrate-resistant acid phosphatase and alkaline phosphatase as respective markers. We are the first to demonstrate that CT suppresses osteoclastic activities in teleosts as well as mammals. Using the sandwich type of an ELISA system with two polyclonal antibodies, we demonstrated that a considerable increase (more than twice) of plasma Ca triggered the secretion of CT from ultimobranchial glands in the feeding period but a slight increase of plasma Ca did not promote CT secretion. From the analyses of the plasma CT level and the expression of a CT receptor, we found that in teleosts, CT has the most important role in the reproductive period compared to other periods. In cartilaginous fish and cyclostomes as well as teleosts, CT has some roles in the reproductive period. These results suggest that CT in fish has a more important role in the reproductive physiology than in the Ca metabolism.

Animals↗
PubMed1990

Development of Dermatophagoides pteronyssinus (Acari: Pyroglyphidae).

Developmental times (egg to adult) and fecundity of the European house dust mite, Dermatophagoides pteronyssinus (Trouessart), were determined for various temperatures that normally occur in the mite microhabitat in homes. Egg-to-adult developmental times were 122.8 +/- 14.5, 34.0 +/- 5.9, 19.3 +/- 2.5, and 15.0 +/- 2.0 d (means +/- SD) at 16 (61 degrees F), 23 (73 degrees F), 30 (86 degrees F), and 35 degrees C (95 degrees F), respectively. Developmental times of individual life stages were consistent proportions of the total egg-to-adult developmental times regardless of temperature. Duration of the egg and protonymphal and tritonymphal life stages were 20-26% of the total development times and for the larval stage, 28-33%. At 23 degrees C, females lived 31.2 +/- 11.1 d and produced 2.5 +/- 0.7 eggs per day during a reproductive period of 26.2 +/- 10.7 d. By comparison, at 35 degrees C, females produced 3.3 +/- 1.3 eggs per day, but female longevity and the reproductive period were reduced to 15.5 +/- 9.6 and 11.6 +/- 6.4 d, respectively. During a lifetime, females produced 68.4 +/- 30.4 and 48.0 +/- 29.6 eggs at 23 and 35 degrees C, respectively.

Animals↗
PubMed2002

Expression of estrogen receptor subtypes in rat pituitary gland during pregnancy and lactation.

The aim of this study was to examine whether the expression levels of mRNA of the three estrogen receptor (ER) subtypes, ERalpha, ERbeta, and truncated ER product-1 (TERP-1) found in the rat pituitary gland were modified during gestation, lactation, and postlactation periods. By using relative quantitative RT-PCR, we found that ERalpha mRNA significantly peaked in midpregnancy. However, the ERalpha protein level remained constant. ERbeta gene expression did not change throughout pregnancy, suggesting that it was not related to estradiol levels during this reproductive period. In contrast, both TERP-1 mRNA and protein levels dramatically increased throughout the second half of gestation, being faintly detectable in early pregnancy. TERP-1 expression was rapidly reversed by lactation, whereas neither pituitary ERalpha nor ERbeta relative levels were significantly altered. In addition, pup removal for 24-96 h on d 9 postpartum significantly reduced the expression of both ERalpha and ERbeta mRNA compared with that in lactating animals, but the expression of TERP-1 mRNA was no longer detected. Collectively, our data indicate that 1) TERP-1, ERalpha, and ERbeta expression levels are differentially regulated in the pituitary; 2) TERP-1 is variably expressed depending on the hormonal environment related to the estrous cycle, pregnancy, and lactation; and 3) TERP-1/ERalpha ratios dramatically change depending on reproductive periods, suggesting a critical role for TERP-1 in reproductive events.

Animals↗
PubMedDate not supplied

[Age-related characteristics of the state of the hypophyseal-gonad-adrenal system in rabbits].

The time-course of changes in testicular and adrenal secretion as well as hypophyseal gonadotropic activity was studied in experimental rabbits during sexual maturity, maximum sex gland functioning at the advanced reproductive period and in the aged animals with lowered gonadal activity. It was shown that activation of testosterone an androstenedione testicular secretion in the mature animals at the reproductive period is replaced by a sharp inhibition of testicular androgenopoiesis in the aged animals. At the same time adrenal testosterone production remains stable over the whole life. The hypophyseal gonadotrophin level negatively correlates with testicular androgen production, but does not depend on adrenal androgen secretion.

Aging↗
PubMed1991

Sex steroid profile and plasma vitellogenin during the annual reproductive cycle of the crested newt (Triturus carnifex Laur.).

The annual reproductive cycle of the crested newt, Triturus carnifex, has been studied in the field. Temperatures, rainfall, humidity, and photoperiod were recorded throughout the year. Adult male and female newts were sampled monthly; snout vent lengths, crest heights of males, and body ovarian, oviducal, testicular, and abdominal gland weights were recorded. Plasma samples were assayed for androgen, estradiol-17 beta, and progesterone by radioimmunoassay and for vitellogenin by enzyme-linked immunosorbent assay. Air, deep water, water surface, and soil temperatures were low from October to March, but increased in April and May without consistent summer variations. Ovarian and oviducal weights increased in October to reach maximum values between January and March (reproductive period). Crest height and abdominal gland weight in males mirrored the ovarian and oviducal pattern, while testicular weights were maximal in October and November. In females, plasma androgens were high during the reproductive period, and plasma estradiol peaked sharply in March, while plasma progesterone changed little. In the males plasma androgen and estradiol concentrations were similar to those of females, while plasma progesterone was significantly correlated with the cycle in testicular weight. In both sexes androgens showed a significantly negative correlation with air and water surface temperature. Plasma vitellogenin peaked in March but it did not correlate with either ovarian weight or plasma estradiol concentrations. These data support and confirm those previously reported for newts under laboratory conditions. The negative correlation between androgens and temperature suggests that this hormone may trigger the reproductive process. Moreover the correlations between plasma progesterone and testicular weight may indicate that this hormone is involved in male newts reproduction.(ABSTRACT TRUNCATED AT 250 WORDS)

Androgens↗
PubMed1999

Seasonal changes in astrocytes parallel neuronal plasticity in the song control area HVc of the canary.

In the song control area HVc of the canary, intercellular dye-coupling among astrocytes was studied by intracellular injection of neurobiotin into identified single astrocytes. Injection of individual astrocytes into acute slices resulted in dye spread to neighboring astrocytes, covering a sphere of up to 1 mm in diameter. The astrocytic nature of the dye-coupled cells was verified by double labeling of neurobiotin-filled cells with antisera for the astrocytic filament proteins GFAP or vimentin. The similarity in the number of dye-coupled cells and the total number of astrocytes labeled by immunocytochemical markers indicate that dye-coupling is specific for astrocytes and labels almost the entire local astrocytic population. Within the major nucleus for vocal control (HVc), approximately 25% more astroglial cells were present than in the surrounding forebrain tissue. There is no apparent hindrance of dye spread at the border of the HVc. The density of dye-coupled astrocytes and the expression of cytoskeletal filament proteins differed markedly between the reproductive period in spring and the quiescent period in autumn. While vimentin is the major astroglial filament in autumn, GFAP is strongly expressed in spring. The density of dye-coupled astrocytes reveals a marked increase in the reproductive period, followed by a reduction in autumn. The data indicate that the astrocytic population in the avian forebrain undergoes significant changes coincident with the known functional changes in the vocal control nuclei during periods of song production.

Age Factors↗
PubMed2005

Evolution of extraordinary female-biased sex ratios: the optimal schedule of sex ratio in local mate competition.

Female-biased sex ratio in local mate competition has been well studied both theoretically and experimentally. However, some experimental data show more female-biased sex ratios than the theoretical predictions by Hamilton [1967. Science 156, 477-488] and its descendants. Here we consider the following two effects: (1) lethal male-male combat and (2) time-dependent control (or schedule) of sex ratio. The former is denoted by a male mortality being an increasing function of the number of males. The optimal schedule is analytically obtained as an evolutionarily stable strategy (ESS) by using Pontrjagin's maximum principle. As a result, an ESS is a schedule where only males are produced first, then the proportion of females are gradually increased, and finally only females are produced. Total sex ratio (sex ratio averaged over the whole reproduction period) is more female-biased than the Hamilton's result if and only if the two effects work together. The bias is stronger when lethal male combat is severer or a reproduction period is longer. When male-male combat is very severe, the sex ratio can be extraordinary female-biased (less than 5%). The model assumptions and the results generally agree with experimental data on Melittobia wasps in which extraordinary female-biased sex ratio is observed. Our study might provide a new basis for the evolution of female-biased sex ratios in local mate competition.

Aggression↗