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PubMed2001

Reproductive investment in pre-industrial humans: the consequences of offspring number, gender and survival.

The number and gender of offspring produced in a current reproductive event can affect a mother's future reproductive investment and success. I studied the subsequent reproductive outcome of pre-industrial (1752-1850) Finnish mothers producing twins versus singletons of differing gender. I predicted that giving birth to and raising twins instead of singletons, and males instead of females, would incur a greater reproductive effort and, hence, lead to larger future reproductive costs for mothers. I compared the mothers' likelihood of reproducing again in the future, their time to next reproduction and the gender and survival of their next offspring. I found that mothers who produced twins were more likely to stop breeding or breed unsuccessfully in the future as compared with women of a similar age and reproductive history who produced a same-gender singleton child. As predicted, the survival and gender of the offspring produced modified the costs of reproduction for the mothers. Giving birth to and raising males generally appeared to be the most expensive strategy, but this effect was only detected in mothers who produced twins and, thus, suffering from higher overall costs of reproduction.

Birth Intervals↗

PubMed2005

F-statistics under alternation of sexual and asexual reproduction: a model and data from schistosomes (platyhelminth parasites).

Accurate inferences on population genetics data require a sound underlying theoretical null model. Nearly nothing is known about the gene dynamics of organisms with complex life cycles precluding any biological interpretation of population genetics parameters. In this article, we used an infinite island model to derive the expectations of those parameters for the life cycle of a dioecious organism obligatorily alternating sexual and asexual reproductions as it is the case for schistosomes (plathyhelminth parasites). This model allowed us to investigate the effects of the degree of mixing among individuals coming from different subpopulations at each new generation (represented in the model by the migration rates before and after clonal reproductions) and the variance in the reproductive success of individuals during the clonal phase. We also consider the effects of different migration rates and degrees of clonal reproductive skew between male and female individuals. Results show that the variance in the reproductive success of clones is very important in shaping the distribution of the genetic variability both within and among subpopulations. Thus, higher variance in the reproductive success of clones generates heterozygous excesses within subpopulations and also increases genetic differentiation between them. Migration occurring before and after asexual reproduction has different effects on the patterns of F(IS) and F(ST). When males and females display different degrees of reproductive skew or migration rates, we observe differences in their respective population genetic structure. While results of the model apply to any organism alternating sexual and clonal reproductions (e.g. all parasitic trematodes, many plants, and all aphididae), we finally confront some of these theoretical expectations to empirical data from Schistosoma mansoni infecting Rattus rattus in Guadeloupe.

Animals↗

PubMedDate not supplied

Living and dying for sex. A theory of aging based on the modulation of cell cycle signaling by reproductive hormones.

A mechanistic understanding of aging has yet to be described; this paper puts forth a new theory that has the potential to explain aging in all sexually reproductive life forms. The theory also puts forth a new definition of aging - any change in an organism over time. This definition includes not only the changes associated with the loss of function (i.e. senescence, the commonly accepted definition of aging), but also the changes associated with the gain of function (growth and development). Using this definition, the rate of aging would be synonymous with the rate of change. The rate of change/aging is most rapid during the fetal period when organisms develop from a single cell at conception to a multicellular organism at birth. Therefore, 'fetal aging' would be determined by factors regulating the rate of mitogenesis, differentiation, and cell death. We suggest that these factors also are responsible for regulating aging throughout life. Thus, whatever controls mitogenesis, differentiation and cell death must also control aging. Since life-extending modalities consistently affect reproduction, and reproductive hormones are known to regulate mitogenesis and differentiation, we propose that aging is primarily regulated by the hormones that control reproduction (hence, the Reproductive-Cell Cycle Theory of Aging). In mammals, reproduction is controlled by the hypothalamic-pituitary-gonadal (HPG) axis hormones. Longevity inducing interventions, including caloric restriction, decrease fertility by suppressing HPG axis hormones and HPG hormones are known to affect signaling through the well-documented longevity regulating GH/IGF-1/PI3K/Akt/Forkhead pathway. This is exemplified by genetic alterations in Caenorhabditis elegans where homologues of the HPG axis pathways, as well as the daf-2 and daf-9 pathways, all converge on daf-16, the homologue of human Forkhead that functions in the regulation of cell cycle events. In summary, we propose that the hormones that regulate reproduction act in an antagonistic pleiotrophic manner to control aging via cell cycle signaling; promoting growth and development early in life in order to achieve reproduction, but later in life, in a futile attempt to maintain reproduction, become dysregulated and drive senescence.

Aging↗

PubMed1986

Perspectives on reproductive and developmental toxicity.

Human reproduction and development is a cycle of interdependent events. Virtually all of its phases have been shown to be the primary target of one or more non-mutagenic exogenous agents. Such agents interfere with certain of the countless epigenetic or ontogenic events essential for normal completion of the cycle. Mutagens disrupt this cycle at some points, but the overwhelming majority of reproductive and developmental toxins are not mutagenic. As in all aspects of toxicology, the reproductive and developmental effects of chemicals are determined by the intrinsic nature of the chemical, the quantity of the chemical exposure, the duration of exposure and the stage of the cycle at which it occurs. Signs of reproductive toxicity range from reduced fertility to spontaneous abortion. Adverse effects on the conceptus are categorized as functional deficits, developmental retardation, structural abnormality and death. One or more of these is anticipated to occur as a result of excess exposure to most chemicals. Although the degree of hazard and risk potential can be calculated in each instance, chemicals differ markedly in their ability to interfere with reproduction (Amann, 1982) and/or development (Johnson, 1984). Standardized methods for reproductive and developmental toxicity safety evaluation are available for detecting adverse effects upon any aspect of reproduction and development. Data currently available establish that these state-of-the-art tests conducted in laboratory animals are often highly predictive of the type of adverse effect a particular chemical will have in humans, as well as the exposure level at which it will occur. By adding a modest safety factor to the no-observed-effect-level of well-executed animal studies, safe human exposure levels can be established. Responsibility for determining the intrinsic hazard potential and the risk estimate of exposure rests with manufacturers and major users of occupational and other environmental chemicals. As public awareness of reproductive and developmental hazards has increased in recent years, it has come to be understood that some chemicals have a predilection for causing reproductive impairment and/or disrupting development in the absence of other toxicity. Such substances must be identified to establish safe exposure levels and to determine the types of effects to be expected, should excessive human exposure occur. The setting of safe exposure levels is necessary both from the standpoints of ensuring public safety and avoiding product liability.

Animals↗

PubMed1987

Biological markers of male reproductive toxicology.

Reproduction is a complex, stepwise series of processes that begins with gametogenesis, continues through gamete interaction, implantation, embryonic development, growth, parturition, and postnatal adaptation, and is completed with the development and sexual maturation of the newly formed organism. These reproductive processes do not take place in a chemically pristine environment, but rather in an environment increasingly contaminated with the products and by-products of the chemical age in which we live. Some environmental pollutants are known to be carcinogenic, mutagenic, or toxic to the reproductive system, but most have not been adequately tested for reproductive toxicity. Just as reproduction is complex, biological mechanisms underlying toxicology are similarly complex and involve absorption, distribution, metabolism (toxification and/or detoxification), excretion, and repair. The synthesis of these sciences into the relatively nascent science of reproductive toxicology includes teratology, pharmacology, epidemiology, and occupational and environmental health. Female reproductive function (especially pregnancy outcome) has historically been the focus of attention, but there is increasing interest in the effects of chemical exposure on male reproductive function. Several reports have documented the physiology, biochemistry, and toxicology of male mammalian reproduction, and evaluated susceptibility of the male to the effects of exogenous chemicals.

Animals↗

PubMed2006

Evolution of reproductive proteins from animals and plants.

Sexual reproduction is a fundamental biological process common among eukaryotes. Because of the significance of reproductive proteins to fitness, the diversity and rapid divergence of proteins acting at many stages of reproduction is surprising and suggests a role of adaptive diversification in reproductive protein evolution. Here we review the evolution of reproductive proteins acting at different stages of reproduction among animals and plants, emphasizing common patterns. Although we are just beginning to understand these patterns, by making comparisons among stages of reproduction for diverse organisms we can begin to understand the selective forces driving reproductive protein diversity and the functional consequences of reproductive protein evolution.

Animals↗

PubMed2001

Description and evaluation of a short-term reproduction test with the fathead minnow (Pimephales promelas).

Due to the time and expense associated with full life-cycle testing, most current toxicity tests with fish do not explicitly consider reproductive output as an endpoint but, rather, focus on early life-stage survival and development. However, some classes of chemicals could adversely impact reproduction at concentrations below those that affect development. Further, estimates of the effects of toxic compounds on reproductive output can be critical to the ecological risk assessment process. In this manuscript, we describe a short-term reproduction test with the fathead minnow (Pimephales promelas) and evaluate the test using two model reproductive toxicants, methoxychlor (an estrogenic compound) and methyltestosterone (an androgenic chemical). The test is initiated with reproductively mature animals and is comprised of a pre-exposure phase of 14 to 21 d, followed by a chemical exposure of up to 21 d. During and at completion of the test, several endpoints related to reproductive fitness and endocrine function are assessed. Both chemicals evaluated in our study caused a significant decrease in fecundity of the fish at nominal concentrations of 5.0 micrograms/L (methoxychlor) and 0.2 mg/L (methyltestosterone). Methoxychlor decreased plasma concentrations of one or more steroids (testosterone, 11-ketotestosterone, beta-estradiol) in both sexes and caused a significant induction of plasma vitellogenin in males, a response consistent with activation of the estrogen receptor by the pesticide (or its metabolites). Methyltestosterone decreased plasma concentrations of sex steroids and adversely affected gonadal status (as evaluated by relative weight and histopathology) in both sexes. The androgenic nature of methyltestosterone was clearly expressed as masculinization of exposed females via formation of nuptial tubercles, structures normally present only in reproductively active males. The chemical also caused a significant induction of plasma vitellogenin in both males and females; this unexpected estrogenic response was most likely due to aromatization of the androgen to a form capable of binding to the estrogen receptor. These studies demonstrate the utility of this short-term assay for identifying chemicals that exert reproductive toxicity through alterations in endocrine systems controlled by estrogens and androgens.

Animals↗

PubMed2005

[Temporal and spatial dynamics of reproductive modules of endangered plant Disanthus cercidifolius var. longipes natural populations].

Based on field observation data, this paper studied the flowering phenology and the temporal and spatial dynamics of the reproductive modules of endangered plant Disanthus cercidifolius var. longipes natural populations. The results showed that there were certain differences of the flowering phenology among the populations in different communities, e. g., in pure forest, the average flowering duration of individuals was the longest (75 d), while the flowering synchrony was the lowest (0.717 d), but in bamboo forest, the flowering duration of individuals was the shortest (47 d), while its flowering synchrony was the highest. The numbers of reproductive branches and inflorescences were increased with increasing individual age, and reached the highest at the age of 30 - 35 yr. At the elevation of 810 m, the numbers of individual reproductive branches and inflorescences reached the peak, and there were significant differences among the crown levels. The reproductive branch number of individuals and the inflorescences per reproductive branch were the highest in pure forest, being 411.39 and 7. 857, respectively, while the inflorescences per reproductive branch in bamboo forest were notably lower than those in other communities. The abortive ratio of reproductive modules of young individuals was higher than that of the older ones in the flower-bud, flowering, and fruit phases. The abortion of reproductive modules had no correlation with their distributed elevation, but some correlations existed with their development time, distributed crown levels and communities. The major factor affecting the abortive ratio of individual reproduction modules was probably the illumination condition in the distributed communities.

Flowers↗

PubMed1988

Computer modeling of human fertility: the impact of reproductive heterogeneity on measures of fertility.

As a result of the paucity of biological markers for both reproductive events and exposure to reproductive toxicants, it is likely that individual members of populations will be misclassified with respect to reproductive performance and xenobiotic exposure. A four-parameter computerized model of fertility (frequency of intercourse, male fecundity, female fecundity, and spontaneous abortion) was developed to explore the effect of misclassification of populations on several measures of fertility. The measures of fertility explored include cumulative percent pregnant, time to pregnancy, cycle specific fertility, and fecundability ratio. The cumulative percent pregnant and time to pregnancy appeared to be insensitive to small changes in reproductive competence. The fecundability ratio decreased in proportion to the size of population exposed to a reproductive toxicant. The three reproductive parameters, time to pregnancy, cumulative percent pregnant, and fecundability, do not appear useful as measures of reproductive heterogeneity in populations. The reproductive heterogeneity of a population was best defined by the change in cycle-specific fertility rate over the period of observation. These simulations suggest that the change in the cycle-specific fertility rate should be evaluated and comparable in all population groups over the period of observation to assure reproductive homogeneity.

Abortion, Spontaneous↗

PubMed1984

Effects of physical forces on the reproductive cycle. Council on Scientific Affairs.

The Council on Scientific Affairs is aware that physicians, as well as the public in general, have expressed increasing concerns regarding the possible adverse effects of various physical forces on the reproductive organs. Various channels of public communication report anecdotal episodes of suspected cause-and-effect relationships between various physical elements in the environment and harmful effects on reproduction. Many of these episodes have not been substantiated by acceptable scientific research. However, some reports have appeared in the scientific literature that do document adverse reproductive effects on humans and animals at certain levels of some physical forces. At levels above 3,636 m (12,000 ft), adverse reproductive effects have been observed in men and women, in the conceptus, and in certain species of animals. Hyperthermia in excess of 40 degrees C may affect the man and the conceptus, as well as the reproductive capacity of certain animals. However, adverse effects of hypothermia have been observed only in animals. Ionizing radiation can cause injury to the man, woman, and conceptus and to animals, depending on dose and duration of exposure. There have been no well-documented injurious effects to the human reproductive organs resulting from radiofrequency-microwave radiation, but there have been some reports in animals that attributed untoward reproductive limitations to thermal effects. To date, there have been no reports in the scientific literature to implicate electronic and magnetic fields, gravity and acceleration, noise, optical radiation (UV, visible, infrared, and lasers), ultrasound, or vibration as having harmful effects on reproduction in either humans or animals. There is need for more well-designed and controlled studies to be performed in all of these areas of exposure at maximum-tolerated levels to physical force before it can be determined with certainty that no ill effects will accrue to the reproductive cycle, especially in assessing harmful effects from low-level exposure during long periods of time.

Atmospheric Pressure↗

PubMed1996

Reproductive and sexual health: a research and developmental challenge.

There is a growing awareness of the burden and implications of reproductive ill health as contributed by unsafe motherhood (during pregnancy, childbirth, abortion), reproductive tract infection (RTIs) and cancer, sexually transmitted infections (STIs) including the human immunodeficiency virus (HIV), poorly regulated fertility, infertility, unwanted pregnancy and adolescent/teenage sexuality and pregnancy. Sexual health further entails a state of well-being in expression of sexuality, prevention of unwanted pregnancies, prevention of STIs and AIDS and freedom from sexual abuse and violence. Reproductive health is increasingly being recognized as one of the corner stones of health and a major determinant and indicator of human social development. It is central to general health as it reflects health in childhood and adolescence and sets the stage for health and life expectancy beyond the reproductive years. It is affected by other health aspects such as nutrition and environment, low birth weight, neonatal and perinatal mortality and morbidity. According to the WHO, reproductive health problems account for more than one third of the total burden of disease in women and more than 10 pc of that in men. The challenges posed by the subordinate status of women, the exclusion of men in reproductive health programmes and the need for shaping adolescents' sexual knowledge and behaviour are viewed against today's poor reproductive and sexual health outcomes in the context of Africa. Education systems, employers and policy makers are challenged to provide adequate STI/HIV education and on-site (school, work, satellite, drop in) control services. Prevention interventions, disease and health trends and their outcome require systematic research in order to impact on policy. Reproductive health education should be universal, especially for adolescents, and its impact assessed against appropriate monitoring criteria such as reproductive morbidity, STI prevalence and abortion complications.

Adolescent↗

PubMedDate not supplied

Couples and reproductive health: a review of couple studies.

Traditionally, fertility and family planning research and programs have focused on women. With the expansion of the field to include reproductive health following the 1994 International Conference on Population in Cairo, the more appropriate focus for most reproductive health components appears to be the sexually active couple. This review of studies of couples and reproductive health outcomes examines reports of objective reproductive events, of attitudes and reproductive intentions, of the effect of each partner's attitudes and intentions, of reproductive outcomes, and of the effectiveness of interventions that target couples compared with those that target one partner or the other. For couples' statements about reproductive events, studies throughout the world typically show identical reports less than 90 percent of the time. Concordance between partners on subjective matters is in the range of 60 to 70 percent. Data based on reports of reproductive intentions from both partners have been shown to lead to better predictions of behavior than have data from only one partner. Finally, reproductive health interventions that target couples are found to be more effective than those directed to only one sex. The evidence clearly justifies a focus on couples.

Decision Making↗

PubMed2003

Role of thyroid hormones in human and laboratory animal reproductive health.

The highly conserved nature of the thyroid gland and the thyroid system among mammalian species suggests it is critical to species survival. Studies show the thyroid system plays a critical role in the development of several organ systems, including the reproductive tract. Despite its highly conserved nature, the thyroid system can have widely different effects on reproduction and reproductive tract development in different species. The present review focuses on assessing the role of thyroid hormones in human reproduction and reproductive tract development and comparing it to the role of thyroid hormones in laboratory animal reproduction and reproductive tract development. The review also assesses the effects of thyroid dysfunction on reproductive tract development and function in humans and laboratory animals. Consideration of such information is important in designing, conducting, and interpreting studies to assess the potential effects of thyroid toxicants on reproduction and development.

Animals↗

PubMed2000

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.

Animals↗

PubMed1996

Mechanisms for distance reproduction in perceptual and motor tasks.

Two experiments were carried out: the control experiment and the doubling-distance experiment. In the control experiment subjects were presented with two visual stimuli whose distance was randomly varied. Subjects were required to reproduce the interstimulus remembered distance in two conditions. In one condition (reproduction by pointing) they pointed to a virtual position in space. In the other condition (visual reproduction) they matched the distance by using two other visual stimuli. In the doubling-distance experiment, distances between the two randomly presented stimuli were half of the distances used in the control experiment. Subjects were required to reproduce the double of the presented distance. As in the control experiment, reproduction was executed in two conditions: reproduction by pointing and visual reproduction. In both experiments variable and constant errors were measured. Pointing kinematics were also analysed. The results of the control experiment showed that subjects underestimated distance in reproduction by pointing, whereas they overestimated distance in visual reproduction. Variable errors increased with increasing distance, whereas they were not influenced by the type of reproduction. In the doubling-distance experiment, subjects generally overestimated distance by the same amount in both conditions. However, overestimation decreased with distance during reproduction by pointing. Pointing kinematics varied between the two experiments. The results of the control experiment confirm the hypothesis that perceptual judgement and visuo-motor transformation are two separate processes during which the same object attributes are independently analysed. However, the results of the doubling-distance experiment suggest that perceptual judgement and visuo-motor transformation use the same mechanisms when object attributes are deduced by mental elaboration.

Acceleration↗

PubMed1998

Adolescent sexual and reproductive behavior: a review of the evidence from India.

Despite the fact that adolescents represent almost one quarter of the Indian population, their reproductive health needs are poorly understood and ill served. This paper documents the existing research on sexual and reproductive health, explores the knowledge and attitudes among this population in India, and highlights limitations of methodologies currently employed in research on adolescent reproductive health in India. One serious limitation is the lack of attention in almost every dimension of their reproductive health, including sexuality, reproductive morbidity, abortion-seeking and reproductive choice. What is needed is more behavioral research that explores the levels, patterns, and sociocultural factors underlying adolescents' reproductive health; assesses adolescent reproductive health needs and ways in which health and information services can be structured to respond to these needs in light of the social, cultural and economic constraints that adolescents face; and explores appropriate methodological alternatives, recognizing the need for community-based research, as well as the difficulties of conducting such research under the sociocultural constraints prevailing in India. At the same time, this review argues for far more attention within programs to address adolescent reproductive health service and information needs.

Abortion, Induced↗

PubMed2000

Sociality, mating system and reproductive skew in marmots: evidence and hypotheses.

Marmot species exhibit a great diversity of social structure, mating systems and reproductive skew. In particular, among the social species (i.e. all except Marmota monax), the yellow-bellied marmot appears quite different from the others. The yellow-bellied marmot is primarily polygynous with an intermediate level of sociality and low reproductive skew among females. In contrast, all other social marmot species are mainly monogamous, highly social and with marked reproductive skew among females. To understand the evolution of this difference in reproductive skew, I examined four possible explanations identified from reproductive skew theory. From the literature, I then reviewed evidence to investigate if marmot species differ in: (1) the ability of dominants to control the reproduction of subordinates; (2) the degree of relatedness between group members; (3) the benefit for subordinates of remaining in the social group; and (4) the benefit for dominants of retaining subordinates. I found that the optimal skew hypothesis may apply for both sets of species. I suggest that yellow-bellied marmot females may benefit from retaining subordinate females and in return have to concede them reproduction. On the contrary, monogamous marmot species may gain by suppressing the reproduction of subordinate females to maximise the efficiency of social thermoregulation, even at the risk of departure of subordinate females from the family group. Finally, I discuss scenarios for the simultaneous evolution of sociality, monogamy and reproductive skew in marmots.

Journal Article↗

PubMed2001

Genetic epidemiology and schizophrenia: a study of reproductive fitness.

Genetic epidemiological studies have demonstrated markedly reduced rates in reproduction among schizophrenic patients. According to evolutionary theory, behavioral and psychological phenotypes are selected based on ecological "fit". Where differential survival or reproductive success exists, genotype frequencies are altered in subsequent generations. In the case of schizophrenia, lower rates of reproduction constitute a negative selection factor that should reduce genes in the population associated with the expression of the disease--ultimately leading to decreases in prevalence. However, studies reveal a stable prevalence of about 1% over time. Attempts to explain the apparent contradiction between negative selection and stable prevalence have taken several forms. One explanation suggests that reproductive rates in relatives of schizophrenic patients are increased--compensating for reproductive loss in affected family members. Family data from schizophrenic patients at the Maryland Psychiatric Research Center were compared with those of healthy volunteers and volunteers with schizophrenia spectrum personality (SSP) disorders. Controlling for important socio-cultural and demographic variables, a multiple regression model revealed a significant increase in the number of siblings associated with schizophrenia. No differences in reproductive fitness were found among normal and SSP volunteers. This observed pattern in reproductive fitness provides one mechanism by which prevalence rates can remain stable despite lower reproductive rates among individuals with schizophrenia. Evidence of increased reproductive fitness in relatives suggests the need to consider the complex interactions of proximate and ultimate (evolutionary) mechanisms in the expression of schizophrenia.

Adult↗