Inbreeding effects on reproductive outcome in a Sudanese population

926 women attending the Obstetrics and Gynaecology Department of the Faculty of Medicine, Khartoum, were investigated to study the inbreeding effects on reproductive profiles and morbidity of the offspring. 49.5% of the women had married their first cousins and 13.8% had married more distant relatives. Altogether, 4,471 pregnancy outcomes were analysed including abortions, still births, neonatal and childhood deaths, physical deformity, mental retardation and other congenital abnormalities. No significant difference in the reproductive loss or net fertility was observed between the inbred and outbred groups. Only the proportions of childhood deaths were found to be significantly higher in the inbred marriages (p less than 0.005). The morbidity was also not affected by the practice of inbreeding.     

Life-history theory, fertility and reproductive success in humans

According to life-history theory, any organism that maximizes fitness will face a trade-off between female fertility and offspring survivorship. This trade-off has been demonstrated in a variety of species, but explicit tests in humans have found a positive linear relationship between fitness and fertility. The failure to demonstrate a maximum beyond which additional births cease to enhance fitness is potentially at odds with the view that human fertility behaviour is currently adaptive. Here we report, to our knowledge, the first clear evidence for the predicted nonlinear relationship between female fertility and reproductive success in a human population, the Dogon of Mali, West Africa. The predicted maximum reproductive success of 4.1+/-0.3 surviving offspring was attained at a fertility of 10.5 births. Eighty-three per cent of the women achieved a lifetime fertility level (7-13 births) for which the predicted mean reproductive success was within the confidence limits (3.4 to 4.8) for reproductive success at the optimal fertility level. Child mortality, rather than fertility, was the primary determinant of fitness. Since the Dogon people are farmers, our results do not support the assumptions that: (i) contemporary foragers behave more adaptively than agriculturalists, and (ii) that adaptive fertility behaviour ceased with the Neolithic revolution some 9000 years ago. We also present a new method that avoids common biases in measures of reproductive success.     

Mating behaviour and fertility in domestic chickens. I. Inbreeding

Mating behaviour of males and females of the Inbred line 420 Single Comb White Leghorn chickens was compared with that of the random-bred Minnesota Marker line in a factorial experiment with two replications. Inbred males showed less frequency of approaching females, waltzing, treading and tail-bending, but did not differ from random-bred males in frequency of attempted and successful mountings. Inbred females showed fewer crouchings and completed fewer matings than random-bred females. Fertility was associated with the interaction of male and female behaviour.     

Inbreeding and fertility in Irish Wolfhounds in Sweden: 1976 to 2007

Background  

Given that no influence of inbreeding on life expectancy could be demonstrated in Irish Wolfhounds in a previous study, it was decided to test the influence of inbreeding and other parameters on fertility in this breed.     

Inbreeding and incompatibility in Trichogramma nr. brassicae: evidence and implications for quality control

Inbreeding effects and incompatibility relationships were examined in strains of the egg parasitoid Trichogramma nr brassicae (Hymenoptera: Trichogrammatidae) from southeastern Australia. Crosses between strains provided weak evidence of incompatibility in a few cases. However sex ratio in crosses within strains tended to be more female-biased than in crosses between strains. Inbreeding was imposed for four generations (F>0.59) of sib mating. The fitness of inbred strains was compared to that of outbred strains generated by crossing the inbred strains. No effects of inbreeding were found for any of the four female traits examined (fecundity, body length, head width and hind tibia length), indicating that T. nr. brassicae is not subjected to inbreeding depression. Inbreeding effects were also not found for male mating success as expected for the haploid sex. There were differences among strains for all traits apart from fecundity, indicating heritable variation. Strain differences for fitness measures were uncorrelated with wasp size. The potential use of inbreeding in the quality control of Trichogramma for mass-release is discussed. Inbreeding may be a useful tool in minimising the effects of laboratory adaptation, thereby extending the useful life of a strain.     

Inbreeding and reproductive parameters among Mennonites in Kansas

Abstract

The relationship between inbreeding and certain reproductive parameters was studied by analyzing the reproductive history questionnaires collected from 194 women who attended a research clinic in the Mennonite community of Goessel, Kansas, and for whom pedigrees were constructed from data at the Mennonite Historical Library and at the Alexanderwohl Church. Five reproductive parameters, age of menarche, age of menopause, length of reproductive span, number of children, and fetal wastage, were compared in inbred and noninbred women. There is no consistent evidence that absence of inbreeding or degree of inbreeding (F = 0.00024—0.0332) significantly affects these reproductive parameters in this sample of Mennonite women. If inbreeding does have an effect on these reproductive variables, it is too small to be detected in this sample.     

Experimental evidence of environmental effects on age-specific reproductive success: the importance of resource quality.

Age-specific access to high-quality resources (e.g. territory or nest site) might be an important determinant for improved reproductive performance with increasing age. I experimentally investigated the effects of territory quality versus other age-related improvements in breeding competence (e.g. foraging skills, breeding experience and local knowledge) on age-specific reproductive success. Territory quality (i.e. territory field layer height) was manipulated in year 2 of northern wheatears (Oenanthe oenanthe) that were breeding in the same territory in two consecutive years. Changing territory quality by changing field layer height had a strong effect on within-individual change in the reproductive success of wheatears. This effect was mainly due to a corresponding change in nest predation risk. When territory quality was kept constant (i.e. no between-year change in territory field layer height), within-individual reproductive success did not change between subsequent years. Thus, age-related improvements in foraging skills, breeding experience and local familiarity had no significant effect on within-individual changes in reproductive success. Increased reproductive success with increased age in northern wheatears is therefore mainly explained by an improved access to high-quality territories with increasing age. I conclude that age-dependent access to high-quality breeding resources might be a widespread phenomenon in nature.     

Inbreeding avoidance and reproductive skew in a cooperative mammal

In animal social groups, socially subordinate individuals frequently show low reproductive success or completely fail to breed. This suppression of subordinate reproduction is currently typically attributed to control by dominant individuals. However, subordinates in cooperative groups often lack access to unrelated mates, and an alternative possibility is that their reproduction is limited by inbreeding avoidance. Using the eusocial Damaraland mole-rat Cryptomys damarensis, this paper provides the first experimental evidence, to our knowledge, for this explanation. Subordinate, non-breeding female mole-rats were given access to unrelated mates while remaining in the presence of dominant females, and many became reproductively active soon after unrelated males were introduced. Inbreeding avoidance and the availability of unrelated mates provides a plausible and untested explanation for variation in reproductive skew across animal societies.     

Inbreeding effects on dental morphometrics in Papio hamadryas

The dentition of nonhuman primates (Papio hamadryas) was utilized to investigate the hypothesis that inbreeding will affect mean tooth size and shape. More than five hundred dental casts were collected from baboons at the Institute of Experimental Pathology and Therapy in Sukhumi, USSR. In addition, inbreeding coefficients for each monkey were obtained from pedigree records, some going back seven to nine generations. Each tooth was measured and scored for the presence of discrete morphological structures. Inbred and outbred groups were differentiated and divided by sex. Statistical analysis shows that for the most part inbred monkeys exhibit larger teeth than outbred monkeys, in both male and female groups. When the tooth area of inbreds was compared to that of outbreds, the differences were significant. However, there were no significant differences in frequency of discrete traits. Therefore, it can be concluded that primate dentition is affected by inbreeding, although dental metrics is a more sensitive indicator than morphology.     

Leptin regulation of reproductive function and fertility.

Leptin, a 16-KD protein secreted primarily by adipose tissue, was first discovered in the search for a satiety signal. When administered into the brain, leptin depresses appetite. Interestingly, hyperphagic, obese, transgenic mice with leptin deficiency were noted to be reproductively incompetent, and administration of leptin restored their fertility. These pivotal observations led to numerous studies on the site of action of leptin within the hypothalamo-hypophyseal-gonadal axis, and a variety of models have been used ranging from the prepubertal condition to fasting suppression of reproductive hormones. The preponderance of studies thus far has focused on how leptin serves as a metabolic signal of energy balance within the neuroendocrine system, particularly as a regulator of GnRH/LH secretion. Less research has been conducted with other components of the reproductive system, but local effects of leptin have been demonstrated in the gonads where hyperleptinemia suppresses steroidogenesis and potentially affects gamete maturation. This presentation will review the major concepts for the role of leptin in the modulation of fertility and will consider the potential use of leptin in assisted reproductive technology and embryo transfer.     

Inbreeding and outcrossing in Yucca whipplei: consequences for the reproductive success of plant and pollinator

Unlike most pollinators, yucca moths are active pollinators of their host plants. Females lay their eggs in the flowers they pollinate, and their larvae feed solely on the resulting seeds. Previous evidence suggests that the yucca moth Tegeticula maculata avoids self-pollinating their host Yucca whipplei . Other yucca moths may self-pollinate more frequently. When pollinating, yucca moths are also reported to fly large distances between plants, bypassing neighbouring plants in the process. We experimentally verify the suggestion of Pellmyr et al . that yucca is more likely to retain fruits from self-pollination if overall fruit set is low. Thus, selection on moths to avoid self-pollinating should be density dependent. We found no evidence that mating with close neighbours resulted in inbreeding depression, thus the moth's long-distance flights between plants are yet to be explained.     

Physical attractiveness and reproductive success in humans: evidence from the late 20th century United States

Physical attractiveness has been associated with mating behavior, but its role in reproductive success of contemporary humans has received surprisingly little attention. In the Wisconsin Longitudinal Study (1244 women, 997 men born between 1937 and 1940), we examined whether attractiveness assessed from photographs taken at age 18 years predicted the number of biological children at age 53–56 years. In women, attractiveness predicted higher reproductive success in a nonlinear fashion, so that attractive (second highest quartile) women had 16% and very attractive (highest quartile) women 6% more children than their less attractive counterparts. In men, there was a threshold effect so that men in the lowest attractiveness quartile had 13% fewer children than others who did not differ from each other in the average number of children. These associations were partly but not completely accounted for by attractive participants' increased marriage probability. A linear regression analysis indicated relatively weak directional selection gradient for attractiveness (β=0.06 in women, β=0.07 in men). These findings indicate that physical attractiveness may be associated with reproductive success in humans living in industrialized settings.     

Lifetime reproductive effort in humans

Lifetime reproductive effort (LRE) measures the total amount of metabolized energy diverted to reproduction during the lifespan. LRE captures key components of the life history and is particularly useful for describing and comparing the life histories of different organisms. Given a simple energetic production constraint, LRE is predicted to be similar in value for very different life histories. However, humans have some unique ecological characteristics that may alter LRE, such as the long post-reproductive lifespan, lengthy juvenile period and the cooperative nature of human foraging and reproduction. We calculate LRE for natural fertility human populations, compare the findings to other mammals and discuss the implications for human life-history evolution. We find that human life-history traits combine to yield the theoretically predicted value (approx. 1.4). Thus, even with the subsidized energy budget and uniqueness of the adult lifespan, human reproductive strategies converge on the same optimal value of LRE. This suggests that the fundamental demographic variables contained in LRE trade-off against one another in a predictable and highly constrained manner.     

Inbreeding effects on reproductive outcome: a study based on a large sample from the endogamous Vadde of Kolleru Lake, Andhra Pradesh, India.

Inbreeding effects on reproductive outcome vis-à-vis fertility, prenatal loss and prereproductive mortality, and secondary sex ratio of live and dead children were examined in a large sample of 2078 women of the Vadde fishing population of Kolleru Lake in Andhra Pradesh, India. Demographically, this population is a single endogamous unit. By using an exponential regression model with the proportion of offspring survival as a dependent variable and the inbreeding coefficient as an independent variable, I further examined the inbreeding effects. The results were compared with results from other fishing groups and other southern Indian and non-Indian populations. The results among the Vadde were consistent with those found for other groups of Telugu-speaking fishermen and several other southern Indian populations in that the effects were neither perceptible nor significant. The average B value and the number of lethal equivalents found for the highly inbred southern Indian populations in general and for the Vadde in particular were much smaller than those from other parts of the world, providing empirical support to Sanghvi's hypothesis on long-term effects of inbreeding.     

Antimutagenic effects in humans.

The application of antimutagenicity studies to human somatic mutation is discussed, with emphasis on the potential for future studies. Five assay-gene combinations are now available for measuring human somatic mutation in lymphocytes and erythrocytes. Results with these combinations have defined the human background levels, and show clear responses of mutant frequency to a variety of mutagens. The testing of antimutagenic effects on background frequencies is feasible, but has not yet been done. The major uncertainty in such studies is the unknown age of mutant cells in the background, since only the newly forming mutants are potentially susceptible to most antimutagenic treatments. Intervention studies in the face of active mutagenicity and the use of other genotoxicity endpoints, such as chromosome aberrations, micronuclei and DNA adducts, are considered briefly.     

Inbreeding effects on fetal growth in Beirut, Lebanon

Effects of consanguineous marriages on offspring's gestational age and anthropometrics at birth were investigated in Beirut through a hospital-based survey of 1,252 newborns. Twenty-five percent of all newborns were inbred, and the mean inbreeding coefficient was 1.25%. Neither prematurity rate nor weight, length, head circumference, and chest circumference (considered individually, or as a whole) showed a significant pattern by type of parental consanguinity. Failure to demonstrate significant inbreeding effects is reported in several other studies and generally interpreted as the long-term result of continued inbreeding practices.