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PubMed2000

Reproductive rights of Egyptian women: issues for debate.

Because the definitions of reproductive health and reproductive rights are so broad, it has been possible in Egypt and elsewhere for one or other issue on the reproductive health agenda to be prioritised to the detriment or exclusion of others, and a comprehensive approach avoided. Reproductive health and rights language was introduced in Egypt around the time of the International Conference on Population and Development in Cairo in 1994. From the moment these concepts were translated into Arabic, activists, scholars and women themselves discussed and debated their meanings and questioned whether Egyptian culture permitted a rights approach of this kind and whether reproductive rights were actually perceived as such by Egyptian women. This paper discusses the language of reproductive rights in relation to cultural specificity in the Egyptian context, Egyptian women's perceptions of reproductive rights, the role of tradition and religion, and the ways in which reproductive rights are taken up under Egyptian law. It analyses some of the arguments used against reproductive rights on these grounds.

Arabs↗

PubMed1989

Genetic segregation and the maintenance of sexual reproduction.

Sexual reproduction confronts evolutionary biology with a paradox: other things being equal, an asexual (all-female) population will have twice the reproductive potential of a competing sexual population and therefore should rapidly drive the sexual population to extinction. Thus, the persistence of sexual reproduction in most life forms implies a compensatory advantage to sexual reproduction. Work on this problem has emphasized the evolutionary advantages produced by the genetic recombination that accompanies sexual reproduction. Here we show that genetic segregation produces an advantage to sexual reproduction even in the absence of an advantage from recombination. Segregation in a diploid sexual population allows selection to carry a single advantageous mutation to a homozygous state, whereas two separate mutations are required in a parthenogenetic population. The complete fixation of advantageous mutations is thus delayed in a heterozygous state in asexual populations. Calculation of the selective load incurred suggests that it may offset the intrinsic twofold reproductive advantage of asexual reproduction and maintain sexual reproduction in diploid populations.

Animals↗

PubMed2002

Low and very low birth weight in infants conceived with use of assisted reproductive technology.

BACKGROUND: The increased risk of low birth weight associated with the use of assisted reproductive technology has been attributed largely to the higher rate of multiple gestations associated with such technology. It is uncertain, however, whether singleton infants conceived with the use of assisted reproductive technology may also have a higher risk of low birth weight than those who are conceived spontaneously. METHODS: We used population-based data to compare the rates of low birth weight (less-than-or-equal 2500 g) and very low birth weight (<1500 g) among infants conceived with assisted reproductive technology with the rates in the general population. RESULTS: We studied 42,463 infants who were born in 1996 and 1997 and conceived with assisted reproductive technology and used as a comparison group 3,389,098 infants born in the United States in 1997. Among singleton infants born at 37 weeks of gestation or later, those conceived with assisted reproductive technology had a risk of low birth weight that was 2.6 times that in the general population (95 percent confidence interval, 2.4 to 2.7). The use of assisted reproductive technology was associated with an increased rate of multiple gestations; however, its use was not associated with a further increase in the risk of low birth weight in multiple births. Among twins, the ratio of the rate of low birth weight after the use of assisted reproductive technology to the rate in the general population was 1.0 (95 percent confidence interval, 1.0 to 1.1). Infants conceived with assisted reproductive technology accounted for 0.6 percent of all infants born to mothers who were 20 years of age or older in 1997, but for 3.5 percent of low-birth-weight and 4.3 percent of very-low-birth-weight infants. CONCLUSIONS: The use of assisted reproductive technology accounts for a disproportionate number of low-birth-weight and very-low-birth-weight infants in the United States, in part because of absolute increases in multiple gestations and in part because of higher rates of low birth weight among singleton infants conceived with this technology.

Adult↗

PubMed2003

A perspective on the importance of reproductive mode in astrobiology.

Reproduction is a vital characteristic of life, and sex is the most common reproductive mode in the eukaryotic world. Sex and reproduction are not necessarily linked mechanisms: Sexuality without reproduction exists, while several forms of asexual reproduction are known. The occurrence of sexuality itself is paradoxical, as it is very costly in evolutionary terms. Most of the hypotheses (more than 20) attempting to explain the prevalence of sex fall into two categories: Sex either creates good gene combinations for adaptation to environments or eliminates bad gene combinations counteracting the accumulation of mutations. In spite of this apparent wealth of beneficial effects of sex, asexuality is not rare. Most eukaryotic, asexual lineages are short-lived and can only persist through the presence of sexual roots, but at least two animal groups, bdelloid rotifers and darwinulid ostracods, seem to claim the status of ancient asexuals. Research on (a)sexuality is relevant to astrobiology in a number of ways. First, strong relationships between the origin and persistence of life in extreme environments and reproductive mode are known. Second, the "habitability" of nonterrestrial environments to life greatly depends on reproductive mode. Whereas asexuals can do equally well or better in harsh environments, they fail to adapt fast enough to changing abiotic and biotic environments. Third, it has been shown that plants reproduce mainly asexually in space, and sperm production and motility in some vertebrates are hampered. Both findings indicate that extraterrestrial life under conditions different from Earth might be dominated by asexual reproduction. Finally, for exchange of biological material between planets, the choice of reproductive mode will be important.

Animals↗

PubMed2006

Selective advantage for sexual reproduction.

This paper develops a simplified model for sexual reproduction within the quasispecies formalism. The model assumes a diploid genome consisting of two chromosomes, where the fitness is determined by the number of chromosomes that are identical to a given master sequence. We also assume that there is a cost to sexual reproduction, given by a characteristic time tau(seek) during which haploid cells seek out a mate with which to recombine. If the mating strategy is such that only viable haploids can mate, then when tau(seek) = 0, it is possible to show that sexual reproduction will always out compete asexual reproduction. However, as tau(seek) increases, sexual reproduction only becomes advantageous at progressively higher mutation rates. Once the time cost for sex reaches a critical threshold, the selective advantage for sexual reproduction disappears entirely. The results of this paper suggest that sexual reproduction is not advantageous in small populations per se, but rather in populations with low replication rates. In this regime, the cost for sex is sufficiently low that the selective advantage obtained through recombination leads to the dominance of the strategy. In fact, at a given replication rate and for a fixed environment volume, sexual reproduction is selected for in high populations because of the reduced time spent finding a reproductive partner.

Biological Evolution↗

PubMed2005

Role of oxidative stress in female reproduction.

In a healthy body, ROS (reactive oxygen species) and antioxidants remain in balance. When the balance is disrupted towards an overabundance of ROS, oxidative stress (OS) occurs. OS influences the entire reproductive lifespan of a woman and even thereafter (i.e. menopause). OS results from an imbalance between prooxidants (free radical species) and the body's scavenging ability (antioxidants). ROS are a double-edged sword - they serve as key signal molecules in physiological processes but also have a role in pathological processes involving the female reproductive tract. ROS affect multiple physiological processes from oocyte maturation to fertilization, embryo development and pregnancy. It has been suggested that OS modulates the age-related decline in fertility. It plays a role during pregnancy and normal parturition and in initiation of preterm labor. Most ovarian cancers appear in the surface epithelium, and repetitive ovulation has been thought to be a causative factor. Ovulation-induced oxidative base damage and damage to DNA of the ovarian epithelium can be prevented by antioxidants. There is growing literature on the effects of OS in female reproduction with involvement in the pathophysiology of preeclampsia, hydatidiform mole, free radical-induced birth defects and other situations such as abortions. Numerous studies have shown that OS plays a role in the pathophysiology of infertility and assisted fertility. There is some evidence of its role in endometriosis, tubal and peritoneal factor infertility and unexplained infertility. This article reviews the role OS plays in normal cycling ovaries, follicular development and cyclical endometrial changes. It also discusses OS-related female infertility and how it influences the outcomes of assisted reproductive techniques. The review comprehensively explores the literature for evidence of the role of oxidative stress in conditions such as abortions, preeclampsia, hydatidiform mole, fetal embryopathies, preterm labour and preeclampsia and gestational diabetes. The review also addresses the growing literature on the role of nitric oxide species in female reproduction. The involvement of nitric oxide species in regulation of endometrial and ovarian function, etiopathogenesis of endometriosis, and maintenance of uterine quiescence, initiation of labour and ripening of cervix at parturition is discussed. Complex interplay between cytokines and oxidative stress in the etiology of female reproductive disorders is discussed. Oxidant status of the cell modulates angiogenesis, which is critical for follicular growth, corpus luteum formation endometrial differentiation and embryonic growth is also highlighted in the review. Strategies to overcome oxidative stress and enhance fertility, both natural and assisted are delineated. Early interventions being investigated for prevention of preeclampsia are enumerated. Trials investigating combination intervention strategy of vitamin E and vitamin C supplementation in preventing preeclampsia are highlighted. Antioxidants are powerful and there are few trials investigating antioxidant supplementation in female reproduction. However, before clinicians recommend antioxidants, randomized controlled trials with sufficient power are necessary to prove the efficacy of antioxidant supplementation in disorders of female reproduction. Serial measurement of oxidative stress biomarkers in longitudinal studies may help delineate the etiology of some of the diosorders in female reproduction such as preeclampsia.

Aging↗

PubMed2006

Workgroup report: Implementing a national occupational reproductive research agenda--decade one and beyond.

The initial goal of occupational reproductive health research is to effectively study the many toxicants, physical agents, and biomechanical and psychosocial stressors that may constitute reproductive hazards in the workplace. Although the main objective of occupational reproductive researchers and clinicians is to prevent recognized adverse reproductive outcomes, research has expanded to include a broader spectrum of chronic health outcomes potentially affected by reproductive toxicants. To aid in achieving these goals, the National Institute for Occupational Safety and Health, along with its university, federal, industry, and labor colleagues, formed the National Occupational Research Agenda (NORA) in 1996. NORA resulted in 21 research teams, including the Reproductive Health Research Team (RHRT). In this report, we describe progress made in the last decade by the RHRT and by others in this field, including prioritizing reproductive toxicants for further study; facilitating collaboration among epidemiologists, biologists, and toxicologists; promoting quality exposure assessment in field studies and surveillance; and encouraging the design and conduct of priority occupational reproductive studies. We also describe new tools for screening reproductive toxicants and for analyzing mode of action. We recommend considering outcomes such as menopause and latent adverse effects for further study, as well as including exposures such as shift work and nanomaterials. We describe a broad domain of scholarship activities where a cohesive system of organized and aligned work activities integrates 10 years of team efforts and provides guidance for future research.

Drug-Related Side Effects and Adverse Reactions↗

PubMed1989

Infertility and bioethical issues of the new reproductive technologies.

The scientific breakthroughs resulting in the delivery of Louise Brown in 1978 have opened the floodgates for an ongoing bioethical discussion about medically assisted reproduction. The majority in our society has accepted in vitro fertilization as an ethically justifiable procedure for infertile couples. The concern persists, however, that new reproductive technology has started us on the course of a slippery slope with potentially dire consequences for the so-created children, the traditional family, and, indeed, for society as a whole. The moral status of the embryo is the central issue in debates about such reproductive developments as the "spare" embryo, embryo freezing, embryo donation, embryo research and micromanipulation. Conflicts of interests between the adult's desire to become a parent and the welfare of the offspring are at the root of moral objections raised against manipulation of human reproduction. Extracorporal conception with the possibility for various gamete donors has also brought the long-practiced procedure of artificial insemination by donor and the potential consequences for the child into the discussion. Surrogate mothering and surrogate gestational mothering force us to redefine the age old dictum mater certa est and can render the child a helpless pawn in parental, emotional, and legal strife. Over the ages, society has through firmly established values exerted control over reproduction and acceptance of the new member in the community. Sex without reproduction was a severe blow to the highly regarded societal belief in parenting as the epitomy of life goals. Reproduction without sex through various technically feasible collaborative means further jolts fundamental traditional values and mandates their re-evaluation. Ethical belief systems are by nature highly charged and fiercely defended. Thus, in a pluralistic society, a consensus on the question "What ought to be done of all that can be done with new reproductive technologies?" is probably unachievable. Heated controversies between interest groups constitute an additional psychological burden complicating the ethical ambiguities for some infertile couples who have to decide about using noncoital conception. The interdisciplinary group report by the ethics committee of the American Fertility Society published in the "Ethical Considerations of the New Reproductive Technologies" constitutes a wide framework of guidelines for rational consideration. It will, one hopes, help to formulate needed regulations because some segments of our society as well as many scientists and physicians in the field believe that not all that potentially can be done ought to be done.(ABSTRACT TRUNCATED AT 400 WORDS)

Ethics, Medical↗

PubMed1999

Utilization of developmental basic science principles in the evaluation of reproductive risks from pre- and postconception environmental radiation exposures.

The subject of the reproductive toxicity of various forms of radiation can be anxiety provoking to the public on two accounts, since reproductive failure engenders an unusual level of guilt and anger in the affected families, and radiation effects are misunderstood and feared by the public. Reproductive problems include an array of genetic and acquired diseases affecting parents and their offspring. Many of these problems are associated with the risk of being induced by preconception and/or postconception exposures to environmental agents. For the various forms of radiation, namely, ionizing radiation, ultrasound, low-frequency electromagnetic fields (EMF), and microwaves, the potential for producing reproductive effects varies considerably with the form of "radiation" and, of course, the dose. Whether the exposure occurs preconceptionally or postconceptionally is another major consideration. In evaluating the actual reproductive risks, we rely on accurate dosimetry and information obtained in epidemiological studies and animal studies. Epidemiological studies must demonstrate consistency of the reproductive finding, and animal studies should be designed to add to the findings of the epidemiological studies. Most importantly, the conclusions must not contradict the basic principles of teratology, genetics, and reproductive biology, and they should be biologically plausible. But frequently important basic science principles are ignored in the evaluation process. Yet developmental basic science principles can be instrumental in refuting or supporting the concern about possible risks. Although there is some overlap with regard to the preconception and intrauterine effects of ionizing radiation, there are significant differences. Preconception effects are mainly stochastic effects, while intrauterine effects are mainly deterministic effects. The stochastic genetic risks are lower than the deterministic risks at equivalent exposures. Thus, it is frequently difficult to demonstrate the occurrence of stochastic effects in populations that have received low preconception exposures to ionizing radiation. The reproductive effects from preconception and intrauterine exposures to electromagnetic fields (low-frequency EMF, video display terminals, microwaves) and ultrasound represent much different problems, since the main effects of microwaves and ultrasound occur because of their hyperthermic effects at high exposures. Low-frequency EMF does not have the capacity to produce hyperthermia, and none of these forms of nonionizing radiation has the specificity to damage the DNA comparable to the specificity of ionizing radiation. Not only do they not have targeted mutagenic effects at the usual exposures that populations receive, they are not cytotoxic at these exposure levels as well. From the viewpoint of biological plausibility, these other forms of radiation are much less likely to have the potential for producing reproductive toxicity at the usual population exposures.

Abnormalities, Radiation-Induced↗

PubMed2001

Reproductive ecology and life history of the human male.

Until recently, the reproductive ecology of human males has not been extensively investigated, primarily as a result of the need for a theoretical framework based on the reproductive constraints and energetics of mammalian males. More specifically, male reproductive ecology has necessitated an integrative interpretation of clinical and anthropological data based on the premise that the evolution of human male life histories has involved selection for physiological mechanisms aimed at optimizing trade-offs between survivorship and reproductive effort. This paper attempts to address this gap in our understanding by presenting the current state of male reproductive ecology, including physiologic data from clinical and anthropological investigations as well as recent theoretical developments. Recent investigations outlining population variation in reproductive endocrine function are discussed within the context of potential sources of variation, including energetic expediture, caloric intake, and developmental canalization during adolescence. Additional summaries of male senescence and behavior are presented to provide a complete overview of male life history. Implications of recent anthropological data on contemporary health issues such as prostate cancer and the development of a male contraceptive are also discussed. Finally, several theories are presented that may contribute to our understanding of the evolution of male life histories and reproductive ecology, including theoretical suggestions involving the role of competition, mate choosiness, and potential constraints on male insemination ability, as well as a theory suggesting that male reproductive ecology may be best understood by analyzing energetic allocation decisions between differing somatic tissues that may be indicative of the competing needs for optimizing survivorship and reproductive effort. Directions for future research are finally considered.

Aging↗

PubMed2004

Patterns of behavior across reproductive states of free-ranging female black-handed spider monkeys (Ateles geoffroyi).

Reports on the behavior of spider monkeys (genus Ateles) describe a suite of 5-6 behaviors that are indicative of an estrous female. This study presents hormonal data as an independent measure of reproductive state to determine if these behaviors are associated with any particular reproductive state or stage of the ovarian cycle. Fecal samples collected from 6 free-ranging female black-handed spider monkeys (Ateles geoffroyi) over the course of 11 months were assayed for estrogen (E1C) and progesterone (PdG) metabolites, using an enzyme immunoassay. Behavioral data collected from the same females were analyzed for patterns associated with different reproductive states. A more detailed analysis of behavioral data associated with reproductively cycling periods determined whether each behavior clustered with copulations or a particular phase in the ovarian cycle. Observations of place-sniffing were more frequent for 4 of 5 females when reproductively cycling. Of all copulations observed, 80% occurred when the female participant was reproductively cycling. In addition, the rates of self-clitoral hold and self-clitoral rub behaviors were significantly higher for 2 of 4 and 4 of 5 of females, respectively, when reproductively cycling. No behavior consistently occurred in association with copulations or with any particular phase in the ovarian cycle. Results from this study suggest that the behaviors tested in this paper can provide some information regarding female spider monkey reproductive state (whether or not she is reproductively cycling), but that they are not indicators of estrus in female spider monkeys.

Animals↗

PubMed2005

Occupational exposures and reproductive health: 2003 Teratology Society Meeting Symposium summary.

Assuring reproductive health in the workplace challenges researchers, occupational safety and health practitioners, and clinicians. Most chemicals in the workplace have not been evaluated for reproductive toxicity. Although occupational exposure limits are established to protect 'nearly all' workers, there is little research that characterizes reproductive hazards. For researchers, improvements in epidemiologic design and exposure assessment methods are needed to conduct adequate reproductive studies. Occupational safety and health programs' qualitative and quantitative evaluations of the workplace for reproductive hazards may differ from standardized approaches used for other occupational hazards in that estimates of exposure intensity must be considered in the context of the time-dependent windows of reproductive susceptibility. Clinicians and counselors should place the risk estimate into context by emphasizing the limitations of the available knowledge and the qualitative nature of the exposure estimates, as well as what is known about other non-occupational risk factors for adverse outcomes. This will allow informed decision-making about the need for added protections or alternative duty assignment when a hazard cannot be eliminated. These policies should preserve a worker's income, benefits, and seniority. Applying hazard control technologies and hazard communication training can minimize a worker's risk. Chemical reproductive hazard training is required for workers by the Occupational Safety and Health Administration's Hazard Communication Standard. The National Institute for Occupational Safety and Health (NIOSH) has formed a National Occupational Research Agenda Team to promote communication and partnering among reproductive toxicologists, clinicians and epidemiologists, to improve reproductive hazard exposure assessment and management, and to encourage needed research.

Female↗

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↗

PubMed1997

Alterations in the reproductive patterns of female mice exposed to xenobiotics.

Chemicals, by virtue of their varied interactions with biological molecules, are expected to differ in the way they may alter female reproduction. Reproductive toxicity may reflect effects either on the female germ cells or on various maternal processes such as ovulation, implantation, pregnancy, and parturition. In either case, the ultimate manifestation of chemical toxicity on female reproduction is a decrease in the number of normal young born. Very little information is available on the effects of chemicals that are nonhormonal in nature on the long-term ability of treated females to produce offspring. This report presents the results of long-term female total reproductive capacity (TRC) tests on 29 chemicals, including pharmaceuticals, pesticides, and alkylating and industrial agents. For each chemical, the minimum test involved an evaluation of the maximum tolerated dose administered as a single intraperitoneal injection. Females were single-pair mated with an untreated male for most of the female's reproductive life span (a minimum of 347 days posttreatment) and scored for the number of live births produced during this period. Confirmatory dominant lethal experiments or histological examinations for numbers of small follicles were carried out when mutagenic effects or cytotoxicity, respectively, were suspected as the basis for reduced fertility. Of the 29 chemicals studied, 17 had reproductive effects which may be grouped into one of three classes: (1) those that reduced the total number of young and litters per female, (2) those that reduced the total number of young but not of litters, and (3) those that had no significant effect on the total number of young produced but reduced the size of the first and/or second litters. The TRC provides a capacity for detecting a range of toxic insults upon female reproduction. Many of the chemicals were indeed shown to affect the reproductive performance of females through mutagenic and/or cytotoxic effects on follicles. In some cases, however, no causative mechanism could be identified for the observed reduction in reproductive performance. Nevertheless, with this report the number of chemicals tested by this TRC procedure has been quadrupled and the categories of chemicals tested have been substantially broadened.

Alkylating Agents↗

PubMed2001

In ovo exposure to polychlorinated biphenyls: reproductive effects on second-generation American kestrels.

The reproductive success of wild birds has been affected by exposure to multiple contaminants. Reproduction of captive American kestrels (Falco sparverius) was suppressed when adult birds were exposed to dietary polychlorinated biphenyls (PCBs). In this study, the reproductive effects of in ovo exposure to PCBs is explored, along with determining effects on reproduction in second-generation birds indirectly exposed to PCBs. Reproductive changes in this subsequent generation are examined separately in male and female birds. Captive American kestrels (F. sparerius) were hatched from clutches with eggs containing environmentally relevant levels of total PCBs (34.0 microg/g whole egg WW versus 0 microg/g controls); parent birds had been fed PCB-spiked (Aroclor 1248:1254:1260) food (7 mg/kg BW day(-1)) for 100 days until their eggs hatched. In 1999, the second-generation PCB birds were paired with unexposed kestrels having reproductive experience. In ovo PCB exposure suppressed egg laying completely in 25% of PCB females and resulted in delays in clutch initiation and smaller clutch sizes for PCB male and female pairs. There was no evidence in this study of in ovo PCB treatment effects on fertility or hatching success. The decline in reproductive success was also reflected in the reduced fledging success and higher incidence of complete brood mortality of PCB nestlings. Differences between in ovo-exposed PCB males and females but not between controls were evident in reproductive success. In ovo PCB exposure appears to have had greater effects on female kestrels until clutch completion, with a greater time lag between pairing and egg laying, reduced numbers of pairs laying eggs, and smaller clutches being laid. In ovo PCB exposure has greater effects later in the breeding season on male kestrels, which had poorer hatching and fledging success relative to the PCB females. Possible behavioral and physiological mechanisms involved in these reproductive changes are discussed.

Animals↗

PubMed2004

Influence of temperature and reproductive state upon the jamming avoidance response in the pulse-type electric fish Brachyhypopomus pinnicaudatus.

The electric organ discharge (EOD) in Brachyhypopomus pinnicaudatus is modified by temperature and reproductive state. We studied the influence of these variables upon a complex behavior, the jamming avoidance response (JAR). Experiments were performed in non-reproductive fish and in two groups of fish after the induction of reproductive state (by nature or by acclimation at 28 degrees C). JARs were elicited at 20 and 30 degrees C by free-run electric stimuli with different deltaLs (interval difference between stimulus and EOD). In non-reproductive fish, JARs induced by stimuli with +deltaLs showed temperature sensitivity, with smaller responses at 30 degrees C. Conversely, similar JARs were obtained at both temperatures in reproductive fish. These observations were replicated in curarized preparations. Stimuli with -deltaLs were almost ineffective in non-reproductive fish at 30 degrees C, whereas adequate JARs were shown by reproductive fish. Phase-locked stimuli were used to evaluate the duration of the low-threshold electrosensory periods preceding and following the EOD. In non-reproductive fish, the temperature step induced a shortening of these periods. The opposite effect was observed in reproductive fish, probably explaining the differences in JAR capability. A prolongation of the low-threshold periods would favor the perception of electrocommunication signals during courtship. JAR changes would be a consequence of this adaptation.

Animals↗

PubMed2005

CO(2) enrichment reduces reproductive dominance in competing stands of Ambrosia artemisiifolia (common ragweed).

Plants growing in dense stands may not equally acquire or utilize extra carbon gained in elevated CO(2). As a result, reproductive differences between dominant and subordinate plants may be altered under rising CO(2) conditions. We hypothesized that elevated CO(2) would enhance the reproductive allocation of shaded, subordinate Ambrosia artemisiifolia L. (Asteraceae) individuals more than that of light-saturated dominants. We grew stands of A. artemisiifolia at either 360 or 720 muL L(-1) CO(2) levels and measured the growth and reproductive responses of competing individuals. To test whether elevated CO(2) altered size and reproductive inequalities within stands, we compared stand-level coefficients of variation (CV) in height growth and final shoot, root, and reproductive organ biomasses. Elevated CO(2) enhanced biomass and reduced the CV for all aspects of plant growth, especially reproductive biomass. Allocation to reproduction was higher in the elevated CO(2) than in the ambient treatment, and this difference was more pronounced in small, rather than large plant positive relationships between the CV and total stand productivity declined under elevated CO(2), indicating that growth enhancements to smaller plants diminished the relative biomass advantages of larger plants in increasingly crowded conditions. We conclude that elevated CO(2) stimulates stand-level reproduction while CO(2)-induced growth gains of subordinate A. artemisiifolia plants minimize differences in the reproductive output of small and large plants. Thus, more individuals are likely to produce greater amounts of seeds and pollen in future populations of this allergenic weed.

Ambrosia↗

PubMed2006

Interactions of the hormones leptin, ghrelin, adiponectin, resistin, and PYY3-36 with the reproductive system.

OBJECTIVE: To summarize the effects of novel hormones (leptin, ghrelin, adiponectin, resistin, and PYY3-36) secreted from adipose tissue and the gastrointestinal tract that have been discovered to exert different effects on several reproductive functions, such as the hypothalamic-pituitary-gonadal axis, embryo development, implantation physiology, and clinically relevant conditions. DESIGN: A MEDLINE computer search was performed to identify relevant articles. RESULT(S): Leptin and ghrelin exert important roles on body weight regulation, eating behavior, and reproduction, acting on the central nervous system and target reproductive organs. As a marker of adequate nutritional stores, these hormones may act on the central nervous system to initiate the complex process of puberty and maintain normal reproductive function. In addition, leptin and ghrelin and their receptors are involved in reproductive events such as gonadal function, embryo development, and embryo-endometrial interaction. CONCLUSION(S): Leptin and ghrelin and other adipose tissue-secreted hormones have significant effects on reproduction. Acting through the brain, these hormones may serve as links between adipose tissue and the reproductive system to supply and regulate energy needs for normal reproduction and pregnancy. Future studies are needed to further clarify the role of these hormones in reproductive events and other related gynecological conditions.

Adiponectin↗