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PubMed2000

The genetic contribution of single male immigrants to small, inbred populations: a laboratory study using Drosophila melanogaster.

This study examined the genetic contribution of single male immigrants to small, inbred laboratory populations of Drosophila melanogaster. Genetic contribution was assessed by measuring the relative frequency of immigrant marker alleles in the first and second generations after immigration, while controlling for any selection effects at the marker locus, and for the experience of male immigrants. When immigrants were outbred, the mean frequency of the immigrant allele was significantly higher than its initial frequency, in both the first and second generations after immigration. There was no significant change in allele frequency for populations receiving inbred immigrants. The increase in allele frequency for outbred immigrants was attributed to an initial outbred vigour fitness advantage of immigrant males over resident males experiencing inbreeding depression. Hybrid vigour of immigrant progeny and the rare-male effect did not have a statistically significant role in the fitness advantage of the immigrant allele. The results suggest that inbreeding may have a considerable impact on the contribution of immigrants to the genetic diversity of populations.

Alleles↗
PubMed2000

Genetic structure in the nonrewarding, bumblebee-pollinated orchid Calypso bulbosa.

Among- and within-population variation at neutral loci is governed by an interaction between stochastic processes and gene flow. A previous study of pollen dispersal in which the transfer of individually marked pollinia was monitored, indicated not only that populations of the nonrewarding, bumblebee-pollinated orchid Calypso bulbosa are connected by substantial levels of gene flow, but also that seed production may be the result of self-fertilization to a considerable extent. We examined the genetic structure of 21 C. bulbosa populations in northern Sweden by F-statistics analyses of variation at three polymorphic allozyme loci. Four populations each consisted of two or three distinct patches, which also allowed us to evaluate among-patch differentiation. The inbreeding coefficient over all loci within populations was high (FIS=0.283). F-statistics indicated that the level of genetic differentiation among patches within populations varied among populations. FST among patches within populations ranged between -0.021 and 0.119 and was significantly different from zero in two of the populations. There was low to moderate genetic differentiation among populations (FST=0. 072). A Mantel test indicated a positive correlation between geographical and genetic distances among populations, but this correlation was dependent on the difference in allele frequencies between the southernmost population sampled and all other populations. Self-fertilization and substructuring within sampling units (within patches and populations) may have contributed to the high inbreeding coefficients observed in many C. bulbosa populations. Long-distance seed and pollen dispersal may account for the low to moderate genetic differentiation among populations.

Animals↗
PubMed2001

Noninvasive paternity assignment in Gombe chimpanzees.

The relative success of chimpanzee male mating strategies, the role of male dominance rank and the success of inbreeding avoidance behaviour can only be assessed when paternities are known. We report the probable paternities of 14 chimpanzees included in a long-term behavioural study of chimpanzees (Pan troglodytes schweinfurthii) at Gombe National Park, Tanzania. DNA samples were collected noninvasively from shed hair and faeces and genotyped using 13-16 microsatellite loci characterized in humans. All 14 offspring could be assigned to fathers within the community. While there is a positive relationship between male rank and reproductive success, we demonstrate that a range of male mating strategies (possessiveness, opportunistic mating and consortships) can lead to paternity across all male ranks. Several adult females were at risk of breeding with close male relatives. Most successfully avoided close inbreeding but in one case a high-ranking male in the community mated with his mother and produced an offspring. In contrast to recent data on chimpanzees (P. t. verus) from the Taï forest, Côte d'Ivoire, no evidence of extra-group paternity was observed in our study. Reanalysis of Taï data using a likelihood approach casts doubt on the occurrence of extra-group paternity in that community as well.

Animals↗
PubMed2003

Estimation of pairwise relatedness between individuals and characterization of isolation-by-distance processes using dominant genetic markers.

A new estimator of the pairwise relatedness coefficient between individuals adapted to dominant genetic markers is developed. This estimator does not assume genotypes to be in Hardy-Weinberg proportions but requires a knowledge of the departure from these proportions (i.e. the inbreeding coefficient). Simulations show that the estimator provides accurate estimates, except for some particular types of individual pairs such as full-sibs, and performs better than a previously developed estimator. When comparing marker-based relatedness estimates with pedigree expectations, a new approach to account for the change of the reference population is developed and shown to perform satisfactorily. Simulations also illustrate that this new relatedness estimator can be used to characterize isolation by distance within populations, leading to essentially unbiased estimates of the neighbourhood size. In this context, the estimator appears fairly robust to moderate errors made on the assumed inbreeding coefficient. The analysis of real data sets suggests that dominant markers (random amplified polymorphic DNA, amplified fragment length polymorphism) may be as valuable as co-dominant markers (microsatellites) in studying microgeographic isolation-by-distance processes. It is argued that the estimators developed should find major applications, notably for conservation biology.

Computer Simulation↗
PubMedDate not supplied

Sexual dimorphism in gender plasticity and its consequences for breeding system evolution.

Flowering plants are able to develop gametes throughout their lives. As a consequence, environmental conditions can impact this development and alter a plant's functional gender or the degree to which it achieves fitness through male or female function. Two dimorphic breeding systems are widespread among angiosperm families: gynodioecy (hermaphrodites and females) and dioecy (males and females). Gynodioecy can evolve into dioecy, via loss of female function on the hermaphrodites, or it can remain stable. Here I discuss how developmental plasticity of gender can impact the sex ratio of populations and thereby influence the transition of one breeding system into another. I review studies showing that greater plasticity of fruit production by hermaphrodites as compared with females causes sex ratios among populations to vary in response to environmental conditions, with higher female frequency expected in harsh or low-quality sites. I also review how dioecy may evolve in dry sites to avoid inbreeding and any consequent inbreeding depression. Taken together, these studies show the importance of understanding how ecological development affects functional gender and consequently the evolutionary stability or malleability of dimorphic breeding systems.

Asteraceae↗
PubMed2004

Stabilizing selection on genomic divergence in a wild fish population.

Conservation programs use breeding protocols to increase genomic divergence (by mating genetically dissimilar individuals) in an attempt to circumvent population declines resulting from inbreeding depression. However, disruption of either beneficial gene complexes or local genetic adaptations can lead to outbreeding depression, and thus, there should be a reduction in fitness of individuals at either end of the genomic divergence continuum. Although such simultaneous inbreeding and outbreeding depression has been observed in plant populations, it rarely has been demonstrated in animal populations. Here, I use both genetic and phenotypic measures to show that there is stabilizing selection on genomic divergence in a wild population of bluegill sunfish (Lepomis macrochirus). I also show that breeding individuals that exercise mate choice produce offspring that are closer to the optimal level of genomic divergence than random mating alone would predict.

Animals↗
PubMed2005

Genetic diversity and reproductive success in mandrills (Mandrillus sphinx).

Recent studies of wild animal populations have shown that estimators of neutral genetic diversity, such as mean heterozygosity, are often correlated with various fitness traits, such as survival, disease susceptibility, or reproductive success. We used two estimators of genetic diversity to explore the relationship between heterozygosity and reproductive success in male and female mandrills (Mandrillus sphinx) living in a semifree ranging setting in Gabon. Because social rank is known to influence reproductive success in both sexes, we also examined the correlation between genetic diversity and social rank in females, and acquisition of alpha status in males, as well as length of alpha male tenure. We found that heterozygous individuals showed greater reproductive success, with both females and males producing more offspring. However, heterozygosity influenced reproductive success only in dominant males, not in subordinates. Neither the acquisition of alpha status in males, nor social rank in females, was significantly correlated with heterozygosity, although more heterozygous alpha males showed longer tenure than homozygous ones. We also tested whether the benefits of greater genetic diversity were due mainly to a genome-wide effect of inbreeding depression or to heterosis at one or a few loci. Multilocus effects best explained the correlation between heterozygosity and reproductive success and tenure, indicating the occurrence of inbreeding depression in this mandrill colony.

Animals↗
PubMed2003

The history of effective population size and genetic diversity in the Yellowstone grizzly (Ursus arctos): implications for conservation.

Protein, mtDNA, and nuclear microsatellite DNA analyses have demonstrated that the Yellowstone grizzly bear has low levels of genetic variability compared with other Ursus arctos populations. Researchers have attributed this difference to inbreeding during a century of anthropogenic isolation and population size reduction. We test this hypothesis and assess the seriousness of genetic threats by generating microsatellite data for 110 museum specimens collected between 1912 and 1981. A loss of variability is detected, but it is much less severe than hypothesized. Variance in allele frequencies over time is used to estimate an effective population size of approximately 80 across the 20th century and >100 currently. The viability of the population is unlikely to be substantially reduced by genetic factors in the next several generations. However, gene flow from outside populations will be beneficial in avoiding inbreeding and the erosion of genetic diversity in the future.

Alleles↗
PubMed2000

Selection-mutation balance in polysomic tetraploids: impact of double reduction and gametophytic selection on the frequency and subchromosomal localization of deleterious mutations.

We modeled the behavior of recessive mutations with deleterious effects to either the sporophyte or the gametophyte, or both, in polysomic tetraploid populations by allowing for varying levels of double reduction, mutation, and self-fertilization. Double reduction causes a decrease of the equilibrium frequencies of deleterious alleles, and it has much more influence on genes subjected to gametophytic selection than on genes solely under sporophytic selection. With gametophytic selection, low frequencies of double reduction are enough to reduce equilibrium frequencies severalfold. Double reduction occurs when sister alleles migrate to the same gamete during meiosis. It depends on the frequency at which a locus recombines with its centromere, and on the frequency of multivalent formation. Therefore, a greater accumulation of deleterious mutations should occur on polysomic chromosomes with a prevalence of bivalent pairing and in chromosomal regions between centromeres and proximal chiasmata. Proximal loci should have a greater impact in reducing the fitness of a polyploid population being inbred. This prediction can explain observations that homozygosities at different subchromosomal regions have distinct effects on inbreeding depression in polyploids. Furthermore, even mildly deleterious alleles can lead to large amounts of inbreeding depression because of their high equilibrium frequencies. Molecular studies correlating level of heterozygosity and degree of heterosis should take into account this nonuniform distribution of deleterious alleles in polyploid genomes. Preservation or enhancement of heterozygosity would be more critical at proximal regions than at other chromosome regions in polysomic polyploid species.

Alleles↗
PubMed1970

A FURTHER ASSESSMENT OF THE ROLE OF FOUNDER EFFECTS IN THE OUTCOME OF Tribolium COMPETITION EXPERIMENTS.

A novel experimental design was employed to further investigate the importance of founder effects in determining the outcome of competition between the flour beetles Tribolium castaneum and T. confusum. Each of 10 replicate cultures in seven competition series was started with 10 pairs of adults of each species that were, in turn, the progeny of 1, 2, 4, 8, 16, 32, or 64 pairs of adults, respectively, from the foundation population. Thus the founder effect occurred one generation prior to the initiation of competition. An analysis of variability among replicate cultures for the first eight monthly censuses showed a significant increase in variation with smaller numbers of original pairs, confirming the hypothesis previously proposed to explain the indeterminate outcome of replicate competition cultures initiated with small numbers of founders. In addition, there was a significant reduction in the rate of elimination of T. confusum with smaller numbers of original pairs. It is suggested that T. castaneum is more sensitive to inbreeding, and that the differential response of the two populations to inbreeding reflects a difference in their homeostatic properties.

Journal Article↗
PubMed1982

Homozygosity and patch structure in plant populations as a result of nearest-neighbor pollination.

The population genetic consequences of nearest-neighbor pollination in an outcrossing plant species were investigated through computer simulations. The genetic system consisted of two alleles at a single locus in a self-incompatible plant that mates by random pollen transfer from a neighboring individual. Beginning with a random distribution of genotypes, restricted pollen and seed dispersal were applied each generation to 10,000 individuals spaced uniformly on a square grid. This restricted gene flow caused inbreeding, a rapid increase in homozygosity, and striking microgeographic differentiation of the populations. Patches of homozygotes bordered by heterozygotes formed quickly and persisted for many generations. Thus, high levels of inbreeding, homozygosity, and patchiness in the spatial distribution of genotypes are expected in plant populations with breeding systems based on nearest-neighbor pollination, and such observations require no explanation by natural selection or other deterministic forces.

Journal Article↗
PubMed1992

Application of DNA fingerprinting to the recovery program of the endangered Puerto Rican parrot.

The Puerto Rican parrot was reduced to approximately 13 animals in 1975 and as a conservation measure, a captive population was established from a few founders taken from the wild between 1973 and 1983. The number of successful breeding pairs in captivity has been low, and the captive breeding program has not been as productive as that of the closely related Hispaniolan parrot. Therefore, a genetic study was initiated to examine the relative levels of relatedness of the captive founders using levels of bandsharing in DNA fingerprints. Unrelated captive founder Puerto Rican parrots had the same average level of bandsharing (0.41) as second-degree relatives of the Hispaniolan parrot (0.38, P > 0.05), with an inbreeding coefficient of 0.04. High levels of bandsharing (> 40%) between pairs of males and females correlated with reproductive failure, suggesting that inbreeding depression is partly responsible for the low number of breeding pairs. Consequently, DNA profiling can be used to guide the captive breeding program for the Puerto Rican parrot, and other endangered species, by identifying pairs of males and females with low levels of bandsharing.

Animals↗
PubMed1993

Disease risk as a cost of outbreeding in the termite Zootermopsis angusticollis.

The effect of the sibship of primary reproductives on mate mortality and the survivorship and growth of incipient colonies was studied in the dampwood termite Zootermopsis angusticollis. Males and females paired with nonsibling mates had higher mortality during the first 10-40 days after pairing, although male and female reproductives showed similar patterns of mortality after colony establishment. The source of mortality appeared to be fungal and/or bacterial pathogens. There were no overall differences in the number of eggs and larvae produced by sibling and nonsibling pairs, and no differences in colony size and biomass 4 years after colony establishment. We therefore could not identify any negative effect of inbreeding in the early phases of colony development. Our results suggest that the risk of exposure to pathogens and the ability of termites to locally adapt to disease could influence the genetic identity of primary reproductives and the extent of inbreeding in termite populations.

Journal Article↗
PubMedDate not supplied

An insight into recent consanguinity within the Basque area in Spain. Effects of autochthony, industrialization and demographic changes.

BACKGROUND: The importance of studying the genetic kinship of those human groups characterized by a deeply rooted ethnicity has traditionally been and still is an interesting goal of anthropological and population genetic studies. However, only a few surveys have aimed to learn about the impact of industrial development on the consanguinity of these populations and even those have concentrated on industrialized regions. This approach is worth analysing in Spain, where industrialization was late in relation to other western European countries. AIM: In this work we analyse the characteristics of inbreeding in Guipúzcoa from 1951 to 1995. This Basque province underwent industrial and tourist development earlier than other Spanish regions. It has the highest density of Basque speakers and has always occupied a central position within the map of distribution of the Basque language. Guipúzcoa is geographically placed in the core of the Basque area. SUDJECTS AND METHODS: Data on consanguineous marriages recorded in the province of Guipúzcoa between 1951 and 1995 were taken from Roman Catholic dispensations stored in the Diocesan Archives of San Sebastián, the province's capital city. Over the whole time period, a total of 1152 consanguineous marriages were registered. RESULTS: The high frequencies of first cousin (M22) (F = 1/16) and uncle-niece, aunt-nephew (M12) (F = 1/8) consanguineous marriages distinguish Guipúzcoa from the rest of Iberian populations. The M22/M33 ratio (with M33 being second cousins) has never dropped below 0.67, which represents a significant deviation from the expectation value of 0.25. When consanguineous marriages are classified according to marriage partner birthplaces interesting results emerge. Provincial endogamy shows the highest consanguinity rates (57%) and the proportion of M22/M33 is also rather high (0.63). However, a major contribution to the consanguinity levels and mean inbreeding coefficient recorded in Guipúzcoa over recent decades has been made by immigrant relative groups coming from other geographical areas of Spain. In this segment of population the observed M22/M33 rates are 1.44. CONCLUSIONS: This study shows again how important preferentiality (or avoidance) is in human consanguinity, and also how human groups, in spite of being spatially settled in the same territory, present differential attitudes for given consanguinity patterns.

Consanguinity↗
PubMedDate not supplied

A study of consanguinity in the Sultanate of Oman.

Omani society has a long tradition of consanguinity, which goes back to pre-Islamic times. The aim of the present study was to determine the prevalence of consanguineous marriage and the mean coefficient of inbreeding in Oman. Consanguinity rates among 60,635 couples (20.8% of the national population of childbearing age) were determined on the basis of a questionnaire in major delivery units. In this large survey, which included all sections of the community, 24.1% of marriages were reported between first cousins and 11.8% of marriages were between second cousins. In addition, a further 20.4% of marriages were contracted within specific tribal groupings. Because of the strictly endogamous nature of the tribal groups in Oman, all marriages would be expected to be consanguineous to some degree, albeit at a level beyond that of second cousins (F < or = 0.0156). To obtain a more detailed picture of the patterns of consanguinity, and to assess the validity of the questionnaire-based study, 500 pedigrees were investigated in detail. The mean coefficient of inbreeding (alpha) in these pedigrees was 0.0204, compared with 0.0198 in the larger survey, suggesting that the data were broadly comparable and confirming the high degree of consanguinity in the population of Oman.

Consanguinity↗
PubMedDate not supplied

Consanguineous marriage in PR China: a study in rural Man (Manchu) communities.

Although there is a long history of consanguineous marriage in China, information on its prevalence is very limited. The Man (Qing) dynasty ruled China for over 250 years, but no consanguinity studies have been reported on this important population. The objective of the present investigation was to determine the present-day level of consanguineous marriage in the Man community, and to compare the data with existing consanguinity information on other Chinese populations. The study was conducted in a group of 11 rural Man communities in the north-eastern Chinese province of Liaoning. Household-based interviews were conducted by local staff on 513 couples, 418 of whom were Man with another 95 Man-Han inter-ethnic marriages. Basic pedigrees were constructed to determine the biological relationship between each set of spouses. Thirty of the 418 couples were in a consanguineous union, with a mean coefficient of inbreeding alpha = 0.0012. The small population sizes of the study may have contributed to the spatial variation in the patterns of inbreeding. Across generations there was a reduction in consanguineous marriages and an increase in inter-ethnic unions, which paralleled changes in civil marriage regulations.

Adult↗
PubMedDate not supplied

Consanguinity in two Uruguayan cities: historical evolution and characteristics (1800--1994).

BACKGROUND: Information about consanguinity in Uruguay is scarce and limited to the end of the 20th century. AIM: To determine the frequency and characteristics of consanguineous marriages, as well as chronological trends, in two Uruguayan cities over almost two centuries. SUBJECTS AND METHODS: We analysed 28,393 Roman Catholic Church marriage records and Diocesan consanguinity dispensations belonging to the cities of Melo (Northeast), and Montevideo (South), for the period 1800--1994. RESULTS: 633 (2.23%) marriages were consanguineous. Among them, first cousin marriages were the most common (58.8% of all consanguineous marriages, including double consanguineous), especially those where the bride and groom were related through their maternal side. During the first decades of the 19th century both regions showed low levels of consanguinity. Consanguinity reached its maximum during the mid-1800s and decreased significantly throughout the 20th century. The overall mean coefficients of inbreeding were moderate in both cases, being greater in the Northeast (alpha=0.00165) than in the South (alpha = 0.00089). CONCLUSIONS: The low level of consanguinity as well as the structure of consanguineous marriages (distribution by degrees) is similar to that found in other southern South American countries. Temporal trends are similar to those found in industrialized regions in Europe, with maximum inbreeding levels during the middle-late 19th century; however, the clear predominance of first cousin unions, differs from most of the data for European countries. Small differences between the two cities can be related to diverse facts, such as socio-economic conditions, ethnic origin, immigration, and sampling.

Consanguinity↗
PubMedDate not supplied

Neural-tube defects in a prehistoric south-western Indian population.

Concern with the frequency and patterning of the occurrence of midline neural-tube defects among contemporary human populations is widespread. These defects are, however, quite old and occur in unusually high numbers of prehistoric skeletons. A common explanation offered for such high incidence has been inbreeding among small, reproductively isolated populations. In a sample of 54 skeletons from the prehistoric south-western Indian site of Tijeras Pueblo in New Mexico, failure of neural-tube closure occurs in 10% of sacra recovered. While a more homogeneous genetic background and inbreeding may account for a portion of this elevated prevalence, the cause appears to lie with cultural-environmental factors. It is suggested that the aetiology of these conditions has become more complex in recent human history.

Adolescent↗