Reproductive compensation in human populations

Reproductive compensation was studied in Russian (family planning) and Middle-Asian (with natural reproduction) urban and rural populations. Questionnaires were used describing postreproductive-age women having at least one pregnancy. The presence of reproductive compensation in a population was identified by comparison of two groups: "loaded" and "unloaded" by values of total and effective fertility. Families with excessive (compared with the mean population value) pregnancy outcome failure (spontaneous abortions, stillbirths, preproductive-age deaths of children) were ascribed to the loaded group. Reproductive compensation was discovered in all populations studied, which indicates that this phenomenon is wide-spread in human populations.     

The genetic-demographic approach in anthropological research. XI. The structure of the reproductive behavior of Khakass families]

A detailed analysis of chronological intervals typical of reproduction process has been carried out in rural Khakassian populations to reveal the mechanisms of natural selection and gene drift. It is shown that the process of reproduction is connected with cultural traditions and economical activity of a population under study. The main characteristics of reproductive family behavior (the whole number of children and sex ratio, birth interval ect.) play a very important role in family and kin relationships, age, sex and marriage-migration structure of the population.     

Durability of information concerning the presence of a gamergate in Diacamma sp. from Japan

In social insects, information on the presence of a queen is known to affect the reproductive behaviour of workers. In the queenless ant Diacamma sp., information of the presence of the gamergate, the functional queen, is transmitted exclusively by direct physical contact between the gamergate and workers. Periodic contacts between the gamergate and each worker are therefore necessary to maintain worker sterility. However, how the difference in the contact interval influences reproductive behaviour of workers is unclear. In the present study, by artificially controlling the exact interval of physical contact between workers with the gamergate, it is shown that the inter‐contact interval influences the worker's reproductive condition (i.e. a longer interval leads to more developed ovaries). This system provides a good opportunity to study the mechanisms underling the colony size dependence of individual as well as colony characteristics.     

Reproductive endocrinology of Syngnathidae

Few studies have examined the underlying hormonal mechanisms that mediate reproductive cyclicity, male pregnancy and reproductive behaviour in syngnathids. Progress in these areas has been hampered by the small size of most species in the family and a lack of validated techniques for assessing endocrine function. Research on a relatively small number of species has suggested that androgens are likely regulators of spermatogenesis and the development of the male brood pouch prior to pregnancy whereas prolactin and corticosteroids synergistically promote brood pouch function during pregnancy. No evidence supports a reversal of reproductive steroid hormone function in sex-role reversed behaviour, but neuropeptides such as arginine vasotocin or isotocin should be examined for their role in regulating parturition and mating behaviour. The diversity of reproductive patterns exhibited by syngnathids suggests that they will provide a unique opportunity to assess how hormonal regulation of integumentary function, gametogenesis and reproductive behaviour have evolved within a teleost lineage. Additionally, their coastal distribution and embryo retention make them potentially important subjects for studies on the effect of endocrine disruption on fitness.     

Population response of rodents to control with rodenticides

We summarize theoretical approaches and practice of rodent pest control in Russia and former USSR during last 50 years. We review literature as well as original data to understand mechanisms of rodent populations recovery after chemical control campaigns in urban areas, agricultural lands and natural foci of plague. Laboratory and field experiments indicate that inherent individual variation in behavioural, physiological and life-history traits provides survival of heterogeneous mix of individuals in residual population with increased resistance to poisonous baits and high reproductive potential that leads to fast recovery of a population. In a series of field experiments with various rodent and lagomorph species (Mus musculus, Rattus norvegicus, Meriones unguiculatus, M.meridianus, M.tamariscinus, Ochotona pallasii) we have shown that patterns of recolonization of depopulated area and mechanisms of population recovery vary among species and depend on species-specific social organization. After control territorial and group-living species demonstrated an increase in mobility and affiliative and marking behaviour and a decrease in intraspecific aggression. The rate of recolonization of treated areas was high due to redistribution of survived individuals and immigration by neighbors. Population recovered to original level due to increased breeding performance and fecundity of both survived residents and immigrants. In contrast, socially-independent species exhibited minor changes in behaviour. Recolonization was mainly due to better survival and recruitment of youngs, so the rate of recolonization was low. Species-specificity of behavioural compensation mechanisms to control should be considered when developing ecologically based rodent management strategies[Current Zoology 55(2):81-91,2009].     

Reproductive compensation

The reproductive compensation hypothesis says that individuals constrained by ecological or social forces to reproduce with partners they do not prefer compensate for likely offspring viability deficits. The reproductive compensation hypothesis assumes that (i) pathogens and parasites evolve more rapidly than their hosts, (ii) mate preferences predict variation in health and viability of offspring, (iii) social and ecological factors keep some individuals from mating with their preferred partners (some are constrained to mate with partners they do not prefer), (iv) all individuals may be induced to compensate, so that (v) variation in compensation is due to environmental and developmental factors affecting between-individual abilities to express compensatory mechanisms. Selection favouring compensation may act through variation in prezygotic physiological mechanisms, zygotic mechanisms, or parental care to eggs or young that enhance offspring health, increasing the likelihood that some offspring survive to reproductive age, often at a survival cost to the parents. Compensation may be through increased number of eggs laid or offspring born, a compensatory effort working during a single reproductive bout that sometimes will match the number of offspring surviving to reproductive age produced by unconstrained parents during the same bout. The reproductive compensation hypothesis therefore predicts trade-offs in components of fitness for breeders, such that parents constrained to mating with a nonpreferred partner, but who compensate sometimes match their current productivity (number of offspring at reproductive age) to unconstrained parents (those breeding with their preferred partners), and, when all else is equal, die faster than unconstrained parents. The reproductive compensation hypothesis emphasizes that reproductive competition is not just between constrained and unconstrained individuals, but also among constrained individuals who do and do not compensate. The reproductive compensation hypothesis may thus explain previously unexplained between-population and within-population, between-individual variation in reproductive success, survival, physiology and behaviour.     

Determinants of condom use among youth in Madagascar

The objective of this study was to identify the key determinants of condom use with regular and casual partners among youth in Madagascar.Data stem from a reproductive health survey conducted in October-December 2000 among a representative sample of 2440 youth aged 15-24 living in Toamasina province. Following theoretical models of behaviour change, logistic regression was used to assess the effect of AIDS awareness,personal risk perception, condom access, perceived condom effectiveness,self-efficacy and social support on condom use. Among sexually experienced youth, only about four in ten males and two in ten females have ever used condoms. Fewer than 15% of youth used a condom in last intercourse with their regular partner. Whether youth will try condoms appears to depend largely on the perceived effectiveness of condoms for family planning, access to a nearby condom source, parental support for condom use, and patterns of risky sexual behaviour. Young males' likelihood of using a condom with a regular partner increases significantly if they perceive condoms to be effective for family planning (OR=11.4; p=0.019). For females, it increases with level of self-efficacy (OR=2 1; p=0.042) and having discussed HIV prevention with someone in the last year (OR=2.8; p=0.022). Among males,condom use with casual partners is significantly higher among those who perceive themselves to be at high risk of sexually transmitted infections(OR=2.3; p=0.014), who believe condoms are effective for family planning(OR=2.8; p=0.048), who have good access to condoms (OR=2.9; p=0.002)and who perceive their parents support condom use (OR=1-7; p=0.048). In conclusion, very few youth in Toamasina are using condoms, highlighting the need to continue and expand adolescent reproductive health interventions. In this low HIV prevalence setting, it is important for these programmes to emphasize that condoms are effective for both pregnancy prevention and STI/HIV prevention.     

Reproductive compensation and human genetic disease

The effects of reproductive compensation on the population genetics of sex-linked recessive lethal mutations are investigated. Simple equations are presented which describe these effects, and so complement existing population genetic theory. More importantly, this type of mutation is responsible for several severe human genetic diseases such as Duchenne muscular dystrophy. It is argued that the applications of three modern reproductive technologies--effective family planning, in utero diagnosis with termination, and embryo sexing--will lead to reproductive compensation. The adoption of any of these technologies may rapidly elevate the frequencies of those mutations which are lethal in childhood. This increase is large, in the order of 33% upwards, and occurs rapidly over two to five generations. It also depends on the source of mutations, the effect being larger if most mutations are paternal. In utero diagnosis and/or embryo sexing increase the frequency of the mutation, but simultaneously decrease disease incidence by preventing the birth of affected offspring. In contrast, effective family planning may rapidly increase both mutation frequency and disease incidence.     

High fertility does not cause spontaneous intrauterine fetal loss: the determinants of spontaneous fetal loss in Egypt

This study is concerned with a major, though relatively neglected, reproductive health issue: fetal loss. In particular, the determinants of spontaneous intrauterine mortality in Egypt are investigated with stress on the demographic determinants. To this end, a conceptual framework is developed. Using pregnancy history data from a national survey conducted in Egypt in 1995, the determinants of spontaneous intrauterine fetal deaths among currently married women aged 18-45 are examined using multiple logistic models. It is found that the probability of intrauterine fetal loss rises with maternal age. The apparent positive association of the risk with gravidity is shown to be an artifact, due to the heterogeneity among women with respect to the risk of pregnancy loss, the consequent selection process, and reproductive compensation behavior according to the "success/failure" stopping rule. Therefore, high fertility cannot be said to cause spontaneous fetal loss. Two other features of a woman's reproduction are of strong significance, namely, her pregnancy history and spacing among pregnancies. Once a woman suffers from spontaneous fetal loss, the probability of undergoing further pregnancy losses rises sharply. And the shorter the pregnancy interval, the higher the probability of pregnancy loss. Pregnancies conceived after long intervals are less likely to end in loss.     

Latitudinal compensation in female reproductive rate of a geographically widespread reef fish

Latitudinal variation in fitness-related traits has often been attributed to local adaptation to climates. In poikilotherms including fishes, lower temperatures and shorter reproductive seasons at high latitudes would be expected to cause a reduction in annual reproductive output of an individual. Theories of latitudinal compensation predict that organisms at high latitudes should evolve compensatory responses for these climatic effects. Therefore, latitudinal compensation in female reproductive rate (egg production rate), that individuals from high latitudes produce eggs at higher rates than those from lower latitudes, is likely to occur. I tested this hypothesis with a latitudinally widespread reef fish Pomacentrus coelestis that is a multiple batch spawner, from three different localities, from temperate to subtropical waters, within Japan. I used common-environment experiments at three different temperatures to compare reproductive capacity among local populations. In the experiments, average inter-spawning intervals were the shortest and average size-specific clutch weight was the heaviest in fish from the most northern locality across all temperatures, showing clear latitudinal clines. Thus, the northern fish can achieve higher reproductive output per unit time both by shortening inter-spawning intervals and increasing size-specific clutch weight. Additionally, faster egg production rate of the northern fish did not result from increased food consumption. This finding suggests that gross egg production efficiency was higher in the northern fish and that northern fish had a superior capacity for reproduction within a season. These results support the prediction that latitudinal compensation occurs in the female reproductive rate of P. coelestis. As the reproductive season of this species decreases drastically with increasing latitude, the observed cline in the reproductive rate must be an adaptive response to the local selective regime, i.e., length of the reproductive season. Such latitudinal compensation in female reproductive rates may be a common pattern in latitudinally widespread fishes.     

Inbreeding effects on fertility in humans: evidence for reproductive compensation.

The effects of inbreeding on prereproductive mortality have been demonstrated in many natural populations, including humans. However, little is known about the effects in inbred individuals who survive to adulthood. We have investigated the effects of inbreeding on fertility among inbred adult Hutterites and demonstrate significantly reduced fecundity among the most inbred Hutterite women, as evidenced by longer interbirth intervals (P=.024) and longer intervals to a recognized pregnancy (P=.010) but not by increased rates of fetal loss (P>.50). These data suggest the presence of recessive alleles that adversely affect fecundity among the population. In contrast, completed family sizes do not differ among the more and the less-inbred Hutterite women who were born after 1920, suggesting that reproductive compensation is occurring among the more-inbred and less-fecund women. This recent reproductive strategy would facilitate the maintenance of recessive alleles and contribute to an overall decline in fertility in the population.     

Relationships between sexual behaviour, dominant follicle area, uterus ultrasonic image and pregnancy rate in mares of two breeds differing in reproductive efficiency

Weak or equivocal expression of oestrous behaviour, related to different level of mares' reactivity, may cause problems in oestrus detection and thus influence the reproductive efficiency. The aim of the study was to test whether a breed characterised by low pregnancy rate and high emotional reactivity (Thoroughbreds) differs in oestrous behaviour from a primitive breed with higher reproductive efficiency (Koniks). Additionally, the follicle size was examined to determine how it influences the intensity of oestrus and uterine ultrasonic image and whether the pregnancy rate differs in relation to the intensity of oestrous behaviour and the size of the dominant follicle(s) area on day preceding ovulation in both breeds. During four reproductive seasons the behaviour of 20 Konik polski (K) and 37 Thoroughbred (T) was observed during daily teasing. Simultaneously, the ultrasonic examinations of the reproductive system were carried out. The behaviour of mares was quantified by scoring on an 8-point scale (behavioural score, BS), according to increasing sexual receptivity. Cross-sectional follicular area (FA) was taken as a product of the two largest perpendicular follicular diameters and mean values for each breed were estimated on 1693 and 1982 mm2 for K and T mares, respectively (P < 0.05). Mares were classified according to the pooled area of dominant follicle (FA) during the preovulatory period: group A (FA < or = breed mean) and group B (FA > breed mean). Uterus image (UI) was scored (1-5) according to the increasing uterine echogenicity. The BS was higher (P < 0.01) in K mares (BS = 5.19) than in T mares (BS = 4.04). The BS was significantly related to increasing follicular area (FA). There was no breed difference in uterus image (UI) score. However, significant regression of UI on FA was found in K mares. The intensity of oestrus was positively related with UI (r = 0.29; P < 0.01) only in K mares, no such relationship was found in T mares. The pregnancy rate was significantly higher for K mares (88.5%) than for T mares (46.0%) and lower for T mares with less intense oestrous behaviour (29.4%) as compared to T mares with more intense oestrus (60.0%). No differences in pregnancy rate was found in mares belonging to A or B group of follicular area. The ascertained weaker oestrous behaviour in Thoroughbred was related to lower pregnancy rate. It is hypothesised that oestrus intensity may be the result of breed differences in the response of the neural system to follicular secretions, or may be an effect of higher incidence of multiple non-synchronic ovulation and/or higher sensitivity to stress in Thoroughbred mares.     

Reproductive compensation in the evolution of plant mating systems

Reproductive compensation, the replacement of dead embryos by potentially viable ones, is known to play a major role in the maintenance of deleterious mutations in mammalian populations. However, it has received little attention in plant evolution. Here we model the joint evolution of mating system and inbreeding depression with reproductive compensation. We used a dynamic model of inbreeding depression, allowing for partial purging of recessive lethal mutations by selfing. We showed that reproductive compensation tended to increase the mean number of lethals in a population, but favored self-fertilization by effectively decreasing early inbreeding depression. When compensation depended on the selfing rate, stable mixed mating systems can occur, with low to intermediate selfing rates. Experimental evidence of reproductive compensation is required to confirm its potential importance in the evolution of plant mating systems. We suggest experimental methods to detect reproductive compensation.     

The delineation of fertility strategies in a tribal population of India: the Koyas of Koraput District,Orissa

Demographic data collected for a tribal population of India, the Koyas of Koraput District, Orissa, were examined in light of 2 models of reproductive behavior associated with the economic value of children: the replacement effect and son survivorship motivation. Both models are united in the concept that infant/child mortality affects subsequent fertility. The database consists of retrospective fertility histories of Koya women who had completed their reproductive period. The total number was 260, with the total offspring numbering 1407. 2 distinct cohorts of women were formed for the purpose of analysis, separated only by the criterion of offspring survival: women who had experienced infant child mortality (129 women with 739 children); and women who completed their reproductive period without suffering offspring loss of this nature (132 women with 668 children). The cohort without child loss had a mean parity of 5.10, lower than the average parity of 5.73 recorded for the cohort whose reproductive histories included at least 1 infant/child death. Age specific marital fertility and birth interval analyses indicated that this differential was because of biological, not behavioral, factors. The age pattern of fertility of females suffering offspring mortality failed to demonstrate a high rate of childbearing in the later age intervals of the reproductive period, a characteristic pattern of couples attempting to "replace" lost offspring. Birth interval analysis pointed to biological "interval effect," whereby infant/child mortality caused a cessation of lactation and hence a shortening of postpartum amenorrhea. Computer simulation further indicated that the higher fertility differential of the cohort experiencing offspring loss still did not result in high son survivorship values. The findings agree with earlier studies indicating that for predemographic transitional populations, economically motivated fertility strategies are ineffectual.     

青藏高原露蕊乌头不同海拔居群的开花持续期与繁殖分配

对青藏高原东部3个不同海拔居群的露蕊乌头(Aconitum gymnandrum)(毛茛科)开花持续期和繁殖分配进行了野外观察和检测试验。结果表明:(1)随着海拔的升高,露蕊乌头的开花持续期时间延长,且不同居群间存在显著差异。(2)露蕊乌头的植株个体越大,繁殖投入越高。(3)露蕊乌头的繁殖分配在地上总生物量中所占的比例随海拔升高而增加。研究认为,露蕊乌头在高海拔地区较高的繁殖分配比例强调了有性繁殖在高山恶劣环境中的重要性,而高海拔地区开花持续期的延长补偿了传粉昆虫的减少并增加了对传粉昆虫的吸引能力。     

Models of Evolution of Reproductive Isolation

Mathematical models are presented for the evolution of postmating and premating reproductive isolation. In the case of postmating isolation it is assumed that hybrid sterility or inviability is caused by incompatibility of alleles at one or two loci, and evolution of reproductive isolation occurs by random fixation of different incompatibility alleles in different populations. Mutations are assumed to occur following either the stepwise mutation model or the infinite-allele model. Computer simulations by using It?'s stochastic differential equations have shown that in the model used the reproductive isolation mechanism evolves faster in small populations than in large populations when the mutation rate remains the same. In populations of a given size it evolves faster when the number of loci involved is large than when this is small. In general, however, evolution of isolation mechanisms is a very slow process, and it would take thousands to millions of generations if the mutation rate is of the order of 10(-5) per generation. Since gene substitution occurs as a stochastic process, the time required for the establishment of reproductive isolation has a large variance. Although the average time of evolution of isolation mechanisms is very long, substitution of incompatibility genes in a population occurs rather quickly once it starts. The intrapopulational fertility or viability is always very high. In the model of premating isolation it is assumed that mating preference or compatibility is determined by male- and female-limited characters, each of which is controlled by a single locus with multiple alleles, and mating occurs only when the male and female characters are compatible with each other. Computer simulations have shown that the dynamics of evolution of premating isolation mechanism is very similar to that of postmating isolation mechanism, and the mean and variance of the time required for establishment of premating isolation are very large. Theoretical predictions obtained from the present study about the speed of evolution of reproductive isolation are consistent with empirical data available from vertebrate organisms.     

Within/between population crosses reveal genetic basis for siring success in Silene latifolia (Caryophyllaceae)

Divergence at reproductive traits can generate barriers among populations, and may result from several mechanisms, including drift, local selection and co-adaptation between the sexes. Intersexual co-adaptation can arise through sexually antagonistic co-evolution, a timely hypothesis addressed in animals but, to our knowledge, not yet in flowering plants. We investigated whether male and female population of origin affected pollen competition success, offspring fitness and sex ratio in crosses within/between six genetically differentiated populations of the white campion, Silene latifolia. Each female was crossed with pollen from one focus male from the same population, and pollen from two focus males from two distinct populations, both as single-donor and two-donor crosses against a fixed tester male with a 2-h interpollination interval (n = 288 crosses). We analysed paternity with microsatellite DNA. Male populations of origin significantly differed for siring success and in vitro pollen germination rates. In vitro pollen germination rate was heritable. Siring success also depended on sex ratio in the female family of origin, but only in between-population crosses. In some female populations, two-donor crosses produced less female-biased sex ratios compared with single-donor crosses, yet in other female populations the reverse was true. Offspring sex ratio varied with donor number, depending on the female population. Within/between population crosses did not differ significantly in seed set or offspring fitness, nor were siring success and offspring fitness significantly correlated. Altogether this suggests reproductive divergence for traits affecting pollen competition in S. latifolia.     

Sex‐specific telomere length and dynamics in relation to age and reproductive success in Cory’s shearwaters

Individuals in free‐living animal populations generally differ substantially in reproductive success, lifespan and other fitness‐related traits, but the molecular mechanisms underlying this variation are poorly understood. Telomere length and dynamics are candidate traits explaining this variation, as long telomeres predict a higher survival probability and telomere loss has been shown to reflect experienced “life stress.” However, telomere dynamics among very long‐lived species are unresolved. Additionally, it is generally not well understood how telomeres relate to reproductive success or sex. We measured telomere length and dynamics in erythrocytes to assess their relationship to age, sex and reproduction in Cory's shearwaters (Calonectris borealis), a long‐lived seabird, in the context of a long‐term study. Adult males had on average 231 bp longer telomeres than females, independent of age. In females, telomere length changed relatively little with age, whereas male telomere length declined significantly. Telomere shortening within males from one year to the next was three times higher than the interannual shortening rate based on cross‐sectional data of males. Past long‐term reproductive success was sex‐specifically reflected in age‐corrected telomere length: males with on average high fledgling production were characterized by shorter telomeres, whereas successful females had longer telomeres, and we discuss hypotheses that may explain this contrast. In conclusion, telomere length and dynamics in relation to age and reproduction are sex‐dependent in Cory's shearwaters and these findings contribute to our understanding of what characterises individual variation in fitness.     

Transgenerational effects of maternal diet on metabolic and reproductive ageing

The early-life environment, in particular maternal diet during pregnancy, influences a wide range of organs and systems in adult offspring. Mounting evidence suggests that developmental programming can also influence health and disease in grand-offspring. Transgenerational effects can be defined as those persisting into an F2 generation, where the F0 mother experiences suboptimal diet during her pregnancy. In this review, we critically examine evidence for transgenerational developmental programming effects in human populations, focusing on metabolic and reproductive outcomes. We discuss evidence from historical cohorts suggesting that grandchildren of women exposed to famine and other dietary alterations during pregnancy may experience increased rates of later health complications than their control counterparts. The methodological difficulties with transgenerational studies in human cohorts are explored. In particular, the problems with assessing reproductive outcomes in human populations are discussed. In light of the relative paucity of evidence available from human cohorts, we consider key insights from transgenerational experimental animal models of developmental programming by maternal diet; data are drawn from a range of rodent models, as well as the guinea-pig and the sheep. The evidence for different potential mechanisms of transgenerational inheritance or re-propagation of developmental programming effects is evaluated. Transgenerational effects could be transmitted through methylation of the gametes via the paternal and maternal lineage, as well as other possible mechanisms via the maternal lineage. Finally, future directions for exploring these underlying mechanisms further are proposed, including utilizing large, well-characterized, prospective pregnancy cohorts that include biobanks, which have been established in various populations during the last few decades.     

Are we failing our teenagers? Value of a family planning service for teenagers within the sexually transmitted disease clinic.

Out of 100 teenage girls attending a sexually transmitted disease clinic for the first time, 77 were found to be using a reliable method of contraception and had similar characteristics to teenage girls attending a family planning clinic. The 23 girls not using any reliable contraception exhibited a different pattern of sexual behaviour and were at high risk of unplanned pregnancy. Subsequently, another group of 23 girls not using contraception when seen at the sexually transmitted disease clinic were actively encouraged to attend a family planning clinic. Their risk of unplanned pregnancy was much reduced, although their pattern of sexual activity was unchanged. Ready availability of contraceptive advice for unprotected teenagers in sexually transmitted disease clinics would reduce their high risk of unplanned pregnancy.