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PubMed2003

Inbreeding pattern and reproductive success in a rural community from Galicia (Spain).

The present paper is based on information on marital patterns and reproductive performance (reconstituted families) in the rural community of Los Nogales, Galicia, Spain. Biodemographic data were used to analyse temporal changes and structure of consanguinity in the population, as well as consanguinity versus reproductive success. Of 2347 marriages celebrated between 1871 and 1977, 5.15% were between relatives (up to third degree). The population's inbreeding coefficient was above the Spanish average after 1890, and levels were high during the first part of the 20th century. A possible underestimation of inbreeding coefficients is attributed to the elevated frequency of extramarital births occurring in the Los Nogales population (13.47%). The structures of consanguineous matings, expressed as C22/C33 and C33/C44, turned out to be 0.86 and 0.82 respectively. Regarding migration, before 1920 consanguinity increased, but net migration was negative. In the period 1920-1929 consanguinity began to decrease, prior to maximum emigration. As for reproductive success, information from 1503 reconstituted families shows that complete fertility was slightly higher among consanguineous families despite a greater infant mortality. Lower infertility in consanguineous matings, as well as lower age at marriage and first maternity, could explain the above results.

Adolescent↗
PubMed1999

The effect of inbreeding and population hybridization on developmental instability in petals and leaves of the rare plant silene diclinis (Caryophyllaceae)

Studies of fluctuating asymmetry (FA), a measure of developmental instability (DI), may provide insights into the importance of genetic factors in the long-term survival of small and isolated populations. In the present study of the rare, endemic plant Silene diclinis, I tested how moderate inbreeding within populations (full-sib crosses) and hybridization between populations influenced levels of developmental instability of petals and leaves, using plants derived from controlled crosses and raised under uniform growth conditions. The area and length of petals and leaves were digitized and measured with an image analysis system, but only bifid petals could be tested for true fluctuating asymmetry (normally distributed left-minus-right values with a mean of zero). Based on a bootstrap procedure, I found little evidence for directional asymmetry and antisymmetry in the area and length of the two lobes of the petals. Only the length measurements showed a significant leptokurtic distribution, which may reflect limited resolution (too few classes) in the image analysis system. Randomization tests were performed to test for differences between crossing treatments. Levels of FA of petal area and petal length were significantly higher for both the inbred and the interpopulation hybrid progenies relative to offspring from crosses between unrelated plants from the same population (control). There was no significant treatment effect on DI of leaves. Comparison of plants in the control group revealed that DI of leaf area was significantly higher than FA of petal area, and that these parameters were uncorrelated. This study demonstrates that FA of petals in Silene diclinis is sensitive to moderate levels of inbreeding and outbreeding, and therefore might serve as an indicator of genetic stress.

Journal Article↗
PubMed2001

High resolution microsatellite based analysis of the mating system allows the detection of significant biparental inbreeding in Caryocar brasiliense, an endangered tropical tree species.

In this work we investigate the mating system of four populations of the endangered tropical tree species Caryocar brasiliense, using genetic data from 10 microsatellite loci. Eight to 10 open-pollinated progeny arrays of 16 individuals, together with their mother tree, were sampled per population. Mating system parameters were estimated under the mixed mating model, implemented by the software MLTR. The single-locus outcrossing rate (ts) varied among loci and populations, but multilocus outcrossing rates (tm) were equal to one for all four populations. Nevertheless, biparental inbreeding (tm - ts) was different from zero for all populations, indicating that outcrossing events may occur between relatives. Our results also indicate that the high polymorphism of microsatellite markers provide an extraordinary resolution to discriminate precisely selfing events from outcrossing events between close relatives. Our results indicate that, although highly outcrossed, C. brasiliense shows high levels of biparental inbreeding, most likely due to the limited flight range of pollinators and restriction in seed dispersal. Furthermore, these results suggest that Cerrado fragmentation could limit gene flow by isolating seed dispersers and territorial small sized bat pollinators inside fragments, increasing the rate of mating between close relatives. The conservation of nonisolated populations in large preserved areas may be necessary to foster outcrossing events between unrelated individuals and thus maintain species viability.

Crosses, Genetic↗
PubMed2001

Microsatellite analysis of the inbreeding grass weed Barren Brome (Anisantha sterilis) reveals genetic diversity at the within- and between-farm scales.

Nine microsatellites were used to screen 131 samples of Barren Brome (Anisantha sterilis: synonym Bromus sterilis) collected from within the fields of three English farms [from Oxfordshire (Oxon), Leicestershire (Leics) and Wiltshire (Wilts)] and eight seeds taken from samples of each of 10 farms across England, UK. Most individuals (approximately 97%) were homozygous. Polymorphism occurred at all nine loci in all three farms sampled at the field scale, and at most loci for nine of the other 10 farm samples. Between three and 11 alleles were found per locus. Gene diversity (D = 1 - summation operator p(i)2) ranged from 0.088 to 0.760. Polymorphism occurred among individuals within and among fields, and farms. Some alleles were found in only one farm. On the basis of the alleles at all nine loci in the 211 sampled plants, a total of 92 (44%) different genotypes was identified. Clustering analysis using the unweighted pair group method with arithmetic averages (UPGMA) for the combined Oxon, Wilts and Leics samples did not cluster them into their respective farms. Similarly, a phenogram of samples from all 10 farms showed considerable mixing of individuals with respect to farm origins. Identification of genotypes on field plans showed evidence of both spatial localization and mixing. Previous reports have suggested that A. sterilis is strictly inbreeding with little intrapopulation variation at the genetic level. Our data reveal that A. sterilis exists as numerous separate and genetically different lines, which are maintained by inbreeding but which very occasionally outcross. Possible explanations for this pattern of high genetic diversity are discussed.

Alleles↗
PubMed1997

Consanguineous marriages in a Saudi population and the effect of inbreeding on prenatal and postnatal mortality.

Consanguineous marriages are strongly favoured in the Saudi population. A population-based study of consanguineous marriages was conducted in the Riyadh area. The prevalence rate of consanguineous marriages was 51.3% with an average inbreeding coefficient of 0.02265, which is high compared with many other countries. The most important variables affecting inbreeding were the regional background of the family (p < 0.001) and the level of education, which was inversely associated with consanguineous marriage (p < 0.001). Perinatal and postnatal mortalities were not significantly different between consanguineous and non-consanguineous families.

Abortion, Spontaneous↗
PubMedDate not supplied

Does inbreeding lead to decreased human fertility?

In most Western countries there is a widespread belief, fostered in part by historical prejudice and religious proscription, that inbreeding in human populations causes a reduction in fertility. Support for this belief has been claimed in HLA-based studies, with increased rates of fetal losses suggested in HLA-compatible unions. To critically assess the overall status of fertility in consanguineous unions, data on 30 populations resident in six countries were collated from a systematic review of the literature. The mean numbers of live births were then compared in four consanguinity test categories, ranging from second cousin to uncle-niece/double first cousin, and corresponding non-consanguineous reference groups. Linear regressions indicated a positive association between consanguinity and fertility at all levels of inbreeding, attaining statistical significance at first cousin level (p < 0.0001). The results were, however, subject to a number of potential limitations, in particular lack of control for important socio-demographic variables. To overcome this problem, data on first cousin marriages were abstracted from the National Family and Health Survey conducted in India during 1992-1993. Multivariate analysis showed that fertility in first cousin unions was positively influenced by a number of variables, including illiteracy, earlier age at marriage and lower contraceptive uptake, but the most important of these parameters were duration of marriage and reproductive compensation. In net terms, consanguinity was not found to be associated either with a significant positive or negative effect on fertility.

Adolescent↗
PubMedDate not supplied

The use of parental isonymy in inbreeding in two Outer Hebridean populations.

The use of isonomic associations between the parents of spouses is described. Scottish marriage registers contain information on the natal surnames of all four parents of spouses and enable all the four possible types of isonymy between pairs of parents to be identified. Thus assumptions about the sex labelling of pedigrees may be tested and inbreeding coefficients calculated using either each type of isonymy singly or by pooling all types to give 'overall' coefficients. By this latter method the number of potential isonomous events is increased to four times the number of marriages. Assumptions about the randomness of migration with regard to sex may also be tested by comparing coefficients of relationship by isonymy calculated using either paternal or maternal natal surnames. Within populations the coefficients should be lower for the more migrant sex: between populations the reverse should be the case. Similarly the intergenerational 'fluxes' of surnames in parents of either sex may be compared as may be similar variation in surname frequencies. Two small Outer Hebridean islands, Scalpay and Berneray were used to test these assumptions. It was concluded that while the sex labelling of pedigrees appeared to be at random, there was considerable variation in the isonymy inbreeding coefficients and that because of the 4 X greater amount of data, 'overall' coefficients are more reliable. In both islands there appeared to be a greater lability in migrational terms of the female population, although it was impracticable to examine all marriages involving residents of the two islands.

Analysis of Variance↗
PubMedDate not supplied

Surnames in Ferrara: distribution, isonymy and levels of inbreeding.

The distributions of surnames in populations of small and large towns are almost exactly linearized by a log-log transformation. This indicates probable fit of genetic models to most such distributions, even when the number of surnames is very large. Genetic parameters can then be conveniently calculated from surname distributions. It was found that inbreeding indicators calculated from isonymy are negatively correlated with the size of the towns from which the names were extracted. It was also found that the levels of inbreeding at present observed in Ferrara have little effect on the frequency of homozygotes for the beta-thalassaemia gene.

Consanguinity↗
PubMedDate not supplied

Estimating inbreeding from the Faculty Office Registers, 1534-1540.

Estimates of inbreeding are rather scarce for British populations. A number of studies, especially of Scottish island populations, have focused on pedigree analysis, whilst others have used survey methods or inference from isonymy. By comparison with continental Europe, however, little is known of the historical development of inbreeding. This is undoubtedly due to the lack of evidence from dispensations to marry blood relatives, which are routinely available in the records of marriage of the Roman Catholic church. The paper uses as its data source the Faculty Office Registers, 1534-1540, which were the product of a new system of issuing dispensations following the Dispensations Act of 1533, and which are among the earliest administrative records of the Church of England, founded as a result of Henry VIII's breach with Rome. Dispensations are recorded in the Faculty Office until 1540, when all prohibitions on marriage beyond the proscribed relationships laid down in Leviticus were lifted. The data suggest surprisingly low levels of consanguineous marriage, including a lack of first-cousin marriages. These findings are discussed in terms of the reliability of the archive, and of the social and religious views attending marriage between blood relatives in the medieval and early modern periods.

Consanguinity↗
PubMedDate not supplied

Inbreeding effects on prereproductive mortality: a case-control study in Saguenay-Lac-Saint-Jean (Québec, Canada) based on a population registry 1838-1971.

Effects of inbreeding on the prereproductive mortality, excluding spontaneous abortions, were investigated among offspring of 251 marriages between first-degree cousins (2:2) and 358 marriages between first-degree cousins once removed (2:3) from Saguenay-Lac-Saint-Jean. A control group matched on the demographic and socioeconomic characteristics of the consanguineous marriages was created. The mortality rates were calculated from a computerized population registry. The stillbirth rate was not significantly higher in the 2:2 and 2:3 groups compared with their respective control groups (p > 0.05). Mortality during the first year was significantly higher in both consanguineous groups (p < 0.01) whereas mortality between 1 and 15 years was not (p > 0.05). In Saguenay-Lac-Saint-Jean, less than 1% of the prereproductive mortality, excluding spontaneous abortions, can be attributed to consanguineous marriages. This study is in agreement with previous reports showing that inbreeding had a minor impact in prereproductive mortality.

Case-Control Studies↗
PubMed1999

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.

Adult↗
PubMed2003

Estimation of the inbreeding coefficient through use of genomic data.

Many linkage studies are performed in inbred populations, either small isolated populations or large populations with a long tradition of marriages between relatives. In such populations, there exist very complex genealogies with unknown loops. Therefore, the true inbreeding coefficient of an individual is often unknown. Good estimators of the inbreeding coefficient (f) are important, since it has been shown that underestimation of f may lead to false linkage conclusions. When an individual is genotyped for markers spanning the whole genome, it should be possible to use this genomic information to estimate that individual's f. To do so, we propose a maximum-likelihood method that takes marker dependencies into account through a hidden Markov model. This methodology also allows us to infer the full probability distribution of the identity-by-descent (IBD) status of the two alleles of an individual at each marker along the genome (posterior IBD probabilities) and provides a variance for the estimates. We simulate a full genome scan mimicking the true autosomal genome for (1) a first-cousin pedigree and (2) a quadruple-second-cousin pedigree. In both cases, we find that our method accurately estimates f for different marker maps. We also find that the proportion of genome IBD in an individual with a given genealogy is very variable. The approach is illustrated with data from a study of demyelinating autosomal recessive Charcot-Marie-Tooth disease.

Charcot-Marie-Tooth Disease↗
PubMed1995

Analysis of inbreeding depression in Agaricus bisporus.

Inbreeding depression was observed in the commercial button mushroom, Agaricus bisporus, by examining two laboratory populations. The outbred population consisted of 20 compatible pairings, 10 homokaryons with each of the homokaryons Ag1-1 and Ag89-65. The inbred population consisted of 104 backcrosses (among which 52 were expected to be sexually compatible) obtained from the pairings of two progenitor homokaryons, Ag1-1 and Ag89-65, with 52 progeny homokaryons derived from the mating between Ag1-1 and Ag89-65. The eight fitness components examined for these two populations were successful matings as identified by the analysis of restriction fragment length polymorphisms, positive mycelial interaction in these successful matings, heterokaryon growth rate, primordium formation by the successful matings, fertile fruiting body formation, time to first break, average number of fruiting bodies per square foot, and average weight per fruiting body. The outcrossed population showed a significant advantage over the inbred population in three of eight fitness components. Two pairs of traits were significantly correlated. The multiplicative fitness ratio of the inbred to the outcrossed population was 0.18. The relevance of inbreeding depression to the evolution of fungal mating systems and to mushroom breeding is discussed.

Agaricus↗
PubMed2001

Inbreeding changes the shape of the genetic covariance matrix in Drosophila melanogaster.

The pattern of genetic covariation among traits (the G matrix) plays a central role in determining the pattern of evolutionary change from both natural selection and random genetic drift. Here we measure the effect of genetic drift on the shape of the G matrix using a large data set on the inheritance of wing characteristics in Drosophila melanogaster. Fifty-two inbred lines with a total of 4680 parent-offspring families were generated by one generation of brother-sister mating and compared to an outbred control population of 1945 families. In keeping with the theoretical expectation for a correlated set of additively determined traits, the average G matrix of the inbred lines remained proportional to the outbred control G matrix with a proportionality constant approximately equal to (1 - F), where F is the inbreeding coefficient. Further, the pattern of covariance among the means of the inbred lines induced by inbreeding was also proportional to the within-line G matrix of the control population with a constant very close to the expectation of 2F. Although the average G of the inbred lines did not show change in overall structure relative to the outbred controls, separate analysis revealed a great deal of variation among inbred lines around this expectation, including changes in the sign of genetic correlations. Since any given line can be quite different from the outbred control, it is likely that in nature unreplicated drift will lead to changes in the G matrix. Thus, the shape of G is malleable under genetic drift, and the evolutionary response of any particular population is likely to depend on the specifics of its evolutionary history.

Animals↗
PubMed2026

Ambrosia beetle invasions are structured by inbreeding, intraspecific hybridisation, and bridgeheads.

When invasive populations establish in regions far from their origin, they may accumulate deleterious mutations that limit population viability and later expansion. Invasions stemming from such bridgehead populations may experience further sequential bottlenecks. However, deleterious mutations can be masked or eliminated when populations outbreed with other lineages. Here, we analyse global invasions of a species complex of persistently inbreeding ambrosia beetles, using genomic data (N=247) from invasive populations in Africa, North America and Australia, and from native populations in Asia. We mostly focus on one species of this complex (Euwallacea fornicatus) which poses a severe threat to tree species worldwide and is rapidly expanding its global range. We uncover a single lineage of this species across California, South Africa, and Western Australia, involving an invasive bridgehead and containing almost no nuclear genetic variation. In South Africa we identify a second lineage that has repeatedly hybridised with the first lineage. Genetic patterns in the native range indicate that such opportunistic outbreeding may be common. Despite lacking nuclear variation, the first lineage contained two CO1 haplotypes that were also observed in every hybrid lineage, pointing to heteroplasmy and possible hybrid origins of this lineage. Native populations had fewer missense mutations than invasive populations, indicating that opportunistic outbreeding may help purge fixed deleterious mutations when local lineage diversity is high. These findings highlight the importance of outbreeding even when inbreeding is common, and they demonstrate the biosecurity threat posed by subsequent gene flow into invasive populations.

Journal Article↗
PubMed1999

An uncoupling of male and sexual egg production leads to reduced inbreeding in the cyclical parthenogen Daphnia

Cyclical parthenogenesis involves an alternation of parthenogenetic and sexual reproduction. In cyclical parthenogens with a short generation time, seasonal succession of clones switching to sexual reproduction at different periods of the growing season entails the risk of severe inbreeding with associated fitness costs. We show, however, that differences in genotype frequencies between males and sexual females result in a substantial reduction in the probability of selfing in natural Daphnia populations. This suggests that responses to male- and sexual egg-inducing stimuli may be uncoupled at the level of individual clones as a mechanism to avoid severe inbreeding.

Journal Article↗
PubMed2001

Genetic consequences of polygyny and social structure in an Indian fruit bat, Cynopterus sphinx. I. Inbreeding, outbreeding, and population subdivision.

Population subdivision into behaviorally cohesive kin groups influences rates of inbreeding and genetic drift and has important implications for the evolution of social behavior. Here we report the results of a study designed to test the hypothesis that harem social structure promotes inbreeding and genetic subdivision in a population with overlapping generations. Genetic consequences of harem social structure were investigated in a natural population of a highly polygynous fruit bat, Cynopterus sphinx (Chiroptera: Pteropodidae), in western India. The partitioning of genetic variance within and among breeding groups was assessed using 10-locus microsatellite genotypes for 431 individually marked bats. Genetic analysis of the C. sphinx study population was integrated with field data on demography and social structure to determine the specific ways in which mating, dispersal, and new social group formation influenced population genetic structure. Microsatellite data revealed striking contrasts in genetic structure between consecutive offspring cohorts and between generations. Relative to the 1998 (dry-season) offspring cohort, the 1997 (wet-season) cohort was characterized by a more extensive degree of within-group heterozygote excess (F(IS) = -0.164 vs. -0.050), a greater degree of among-group subdivision (F(ST) = 0.123 vs. 0.008), and higher average within-group relatedness (r = 0.251 vs. 0.017). Differences in genetic structure between the two offspring cohorts were attributable to seasonal differences in the number and proportional representation of male parents. Relative to adult age-classes, offspring cohorts were characterized by more extensive departures from allelic and genotypic equilibria and a greater degree of genetic subdivision. Generational differences in F-statistics indicated that genetic structuring of offspring cohorts was randomized by natal dispersal prior to recruitment into the breeding population. Low relatedness among harem females (r = 0.002-0.005) was primarily attributable to high rates of natal dispersal and low rates of juvenile survivorship. Kin selection is therefore an unlikely explanation for the formation and maintenance of behaviorally cohesive breeding groups in this highly social mammal.

Animals↗
PubMed1996

Autosomal recessive disorders in Saguenay-Lac-Saint-Jean (Quebec, Canada): a study of inbreeding.

Saguenay Lac-Saint-Jean (SLSJ) is a geographically isolated region of northeastern Quebec in which several autosomal recessive disorders have a high incidence. We calculated the inbreeding coefficients of 567 probands and compared them to 1701 matched control individuals. The mean inbreeding coefficient of the group containing all 567 probands was 2.73 times higher than that of the controls (0.001772 versus 0.00065). Thirteen percent (75/567) of the probands were inbred, but only 5% were born to matings between spouses related as second-degree cousins or closer. No marriage between uncle and niece and only two marriages between first-degree cousins were identified in the disorder group. These results strongly suggest that the high incidence of the autosomal recessive disorders in SLSJ is the result of a founder effect.

Consanguinity↗