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PubMed2001

Inbreeding and effective population size of Japanese Black cattle.

The objective of this research was to estimate the amount of inbreeding and effective population size of the Japanese Black breed using pedigree records from bulls and heifers registered between 1985 and 1997. Inbreeding was quantified by three F-statistics: actual inbreeding, inbreeding expected under random mating, and inbreeding due to population subdivision. During the period of 1985 to 1997, the inbreeding expected under random mating increased from 2.3% to 5.0%, whereas the increase of actual inbreeding was more gradual (from 4.7% to 5.4%). The inbreeding due to population subdivision decreased almost linearly and reached 0.5% in 1997, indicating that genetic subdivision of the Japanese Black cattle population has essentially disappeared. The effective size of the breed was estimated from the increasing rate of inbreeding expected under random mating. In the earlier half of this period (1986 to 1990), the breed maintained an effective size of approximately 30. However, after 1991 the effective size sharply decreased and the harmonic mean between 1993 and 1997 was only 17.2. The main cause of this reduction of the effective size was considered to be the intensive use of a few prominent sires. To increase the effective size, an upper limit in the use of AI semen per sire should be imposed.

Animals↗
PubMed2000

Effects of inbreeding on production and survival in Jerseys.

Responses of registered Jersey cows to various levels of inbreeding were examined with pedigree data supplied by the American Jersey Cattle Association and test-day production data from 1970 through 1998 obtained from the Animal Breeding Center at Cornell University. Rate of increase in level of inbreeding is accelerating with time, making it more difficult for producers to make matings that avoid the potentially deleterious effects of inbreeding. Production losses caused by inbreeding were significant and curvilinear for all traits studied except somatic cell linear score, with the greatest losses at higher levels of inbreeding. Inbreeding was found to have the greatest effect on production at early ages and early in lactation. Early onset of the deleterious effects of inbreeding resulted in larger net present value losses than if effects of inbreeding occurred later in the life of an animal. Losses were probably enhanced because of the need to freshen animals as early as possible to maximize net present value returns. Survival decreased as level of inbreeding increased and was likely to have a greater negative impact on the financial health of the dairy enterprise than production losses.

Age Factors↗
PubMed1992

Inbreeding in Swiss Braunvieh and its influence on breeding values predicted from a repeatability animal model.

Inbreeding coefficients were computed for 910,444 animals of the Swiss Braunvieh population. Of the animals born in 1984, 71.5% were inbred with 67.9, 3.4, and .2% having inbreeding coefficients between greater than 0 and 5%, greater than 5 to 10%, and greater than 10%, respectively. The average inbreeding coefficient was 1.14% but, for animals with both parents and at least one grandparent known, it was 1.67%. Breeding values for total milk, fat, and protein yields and for fat and protein percentages were predicted using a repeatability animal model including a regression on the inbreeding coefficient. Phenotypic performance was sizeably depressed for milk yield only (-26 kg/% of inbreeding or 2.4% of the phenotypic standard deviation). Adjusting for inbreeding increased the estimated genetic trend slightly. Inbreeding is only partially accounted for when it is ignored in the construction of the inverse of the numerator relationship matrix. This effect was investigated by comparing predicted breeding values from a model including the complete matrix with predicted breeding values from a model including a matrix constructed with inbreeding ignored. Only .8% of all predicted breeding values were affected by more than +/- 5.5 kg. The maximum difference observed was 55.3 kg. The observed average absolute differences between the breeding values of offspring predicted with the two models increased with inbreeding of parents.

Animals↗
PubMed2004

Curvilinear inbreeding effects on some performance traits in laying hens.

Quadratic partial regression coefficients were estimated for the inbreeding level on five performance traits (body weight, average egg weight, age at first egg, percentage of fertilized eggs, and hatchability of set eggs) of two strains of laying hens. Data on 5631 of H77 layers and 3563 of N88 layers from nine consecutive generations were analysed. Only dams were accounted for. Partial regression coefficients were estimated by REML with a single-trait animal model, which included fixed effects (generation and hatching period) and random effects (additive genetic and error effects). The mean inbreeding level was 0.87% in strain H77 and 1.08% in strain N88. The inbreeding effects were analysed based on the quadratic partial regression equations. A slight inbreeding depression was found for all the traits analysed in N88. In strain H77, negative effects of inbreeding were only noted for body weight and average egg weight. The small inbreeding effects shown here resulted from a relatively low level of homozygosity in the populations studied. The strains were found to differ in the effects of inbreeding. It is worth pointing out that differences were noted both between the inbreeding depression estimated from the partial linear regression equation and the quadratic partial regression equation, as well as different inbreeding levels.

Animals↗
PubMed2006

Inbreeding avoidance and the evolution of gender dimorphism in Wurmbea biglandulosa (Colchicaceae).

How females establish in populations of cosexuals is central to understanding the evolution of gender dimorphism in angiosperms. Inbreeding avoidance hypotheses propose that females can establish and be maintained if cosexual fitness is reduced because they self-fertilize, and their progeny express inbreeding depression. Here we assess the role of inbreeding avoidance in maintaining sexual system variation in Wurmbea biglandulosa. We estimated costs of self-pollination, mating patterns, and inbreeding depression in gender monomorphic (cosexuals only) and dimorphic (males and females) populations. Costs of selfing, estimated from seed set of experimentally self- and cross-pollinated flowers, were severe in both males and cosexuals (inbreeding depression, sigma = 0.86). In a field experiment, intact males that could self produced fewer seeds than both emasculated males and females, whereas seed set of intact and emasculated cosexuals did not differ. Thus, pollinator-mediated selfing reduces fitness of males but not cosexuals under natural conditions. Outcrossing rates of males revealed substantial selfing (t = 0.68), whereas females and cosexuals were outcrossed (0.92 and 0.97). For males, progeny inbreeding coefficients exceeded parental coefficients (0.220 vs. 0.009), whereas for females and cosexuals these coefficients did not differ and approached zero. Differences in coefficients between males and their progeny indicate that selfed progeny express severe inbreeding depression (sigma = 0.93). Combined with inbreeding depression for seed set, cumulative sigma = 0.99, indicating that most or all selfed zygotes fail to reach reproductive maturity. We propose that present sexual system variation in W. biglandulosa is maintained by high inbreeding depression coupled with differences in selfing rates among monomorphic and dimorphic populations.

Biological Evolution↗
PubMed2004

Inbreeding effects on metrical phenotypes among North Indian Children.

This study aimed to examine the effects of inbreeding on 12 quantitative phenotypes like body weight, height, sitting height, head circumference, head length, head breadth, chest circumference, verbal, performance and full scale intelligence quotients, systolic and diastolic blood pressures among North Indian Children. The sample consisted of 3,253 subjects (1,683 males and 1,570 females) including offspring of first cousins, first cousins once removed, second cousins, (inbred part of samples) and unrelated spouses (non-inbred part of samples) ranging in age from 6 to 14 years from the Aligarh district, Uttar Pradesh in North India. Samples were selected purposively to estimate the average inbreeding coefficients based on 3 ancestral generations and using Wright's path method. The average inbreeding coefficient of the present inbred part of sample is 0.04609. The mean ages of males and females were almost equal for both inbred and non-inbred individuals. A significant reduction of means (p < 0.05) or inbreeding depression has been observed in inbred series for all anthropometric and psychometric traits for both the sexes. A significant elevation of mean with inbreeding is observed for systolic and diastolic blood pressure. The average inbreeding depression per 10% inbreeding appeared very high in verbal IQ (> or =23), performance IQ (> or =40), full scale IQ (> or =28), systolic blood pressure (> or =10) and diastolic blood pressure (> or =12) among both sexes. On the whole, relatively greater amount of inbreeding effects are apparent among all measures of intelligence quotient and blood pressures compared to the anthropometric traits. The results of the present work have thrown light on the nature and mechanism of genetic effects of inbreeding on certain quantitative traits in human.

Adolescent↗
PubMed1997

Effects of inbreeding in three life stages of Drosophila buzzatii after embryos were exposed to a high temperature stress.

The interaction between inbreeding and high-temperature stress was examined in the cactophilic fruit fly, Drosophila buzzatii. Embryos of four inbreeding levels (F = 0, F = 0.25, F = 0.375, F = 0.5) were either maintained at 25 degrees C throughout egg-to-adult development or were exposed to 41.5 degrees C for 110 min at an age of 20 h. Hatching, larva-to-pupa survival, pupa-to-adult survival, and egg-to-adult survival were estimated. Heat shock reduced hatching rates, but survival to adulthood for individuals that hatched was unaffected by the heat shock. Inbreeding reduced the proportion of eggs hatching in the 25 degrees C control group only. For larva-to-pupa and pupa-to-adult survival there was no interaction between inbreeding and stress. The effect of inbreeding on egg-to-adult survival was stronger in the 25 degrees C control group compared with the group exposed to heat shock. The results imply environmental dependency of inbreeding depression and suggest that stress tolerance may not always be reduced by inbreeding. The thermal microenvironment of cactus rots in the field was assessed by measuring temperatures inside 17 rots. Internal rot temperatures varied with a maximum temperature of 48 degrees C during the day. Selection for temperature tolerance in nature may have depleted genetic variation for this trait limiting the effect of inbreeding on thermal resistance.

Animals↗
PubMed2003

Inbreeding depression in fecundity and inbred line extinction in the bulb mite, Rhizoglyphus robini.

This study investigated the magnitude of inbreeding depression in fecundity, and whether the depression is purged during six generations of sib mating in the bulb mite, Rhizoglyphus robini. The progeny resulting from a single generation of brother-sister mating suffered significant inbreeding depression in fecundity. During the following six generations of continuous sib-mating, 58% lines were lost, 45% because of sterility and 13% because of preadult mortality. The lines were then outcrossed, and their inbreeding depression compared with that of the base population. The inbreeding depression for the outcrossed population was 0.15, and for the base population 0.19, but the difference was not significant. The lack of significant purging of inbreeding depression indicates that it was caused either by detrimental genes of small effect, or by the breaking down of overdominant relations between alleles. However, the large proportion of extinct lines points to the former mechanism as a predominant cause of inbreeding depression. Theory predicts that the probability of line extinction with inbreeding increases with its load of mutations. If phenotypic variation in fecundity was partly because of differences in numbers of mutations carried by individuals, the fecundity of the line founder could be expected to correlate with the probability that the line derived from it will survive long-term inbreeding. Indeed, fecundity of founder females was significantly associated with line survival, which suggests that line extinction rate may be used as a method to study individual mutational loads, for example, in studies of sexual selection.

Animals↗
PubMed2004

Understanding the relationship between the inbreeding coefficient and multilocus heterozygosity: theoretical expectations and empirical data.

Geneticists have been interested in inbreeding and inbreeding depression since the time of Darwin. Two alternative approaches that can be used to measure how inbred an individual is involve the use of pedigree records to estimate inbreeding coefficients or molecular markers to measure multilocus heterozygosity. However, the relationship between inbreeding coefficient and heterozygosity has only rarely been investigated. In this paper, a framework to predict the relationship between the two variables is presented. In addition, microsatellite genotypes at 138 loci spanning all 26 autosomes of the sheep genome were used to investigate the relationship between inbreeding coefficient and multilocus heterozygosity. Multilocus heterozygosity was only weakly correlated with inbreeding coefficient, and heterozygosity was not positively correlated between markers more often than expected by chance. Inbreeding coefficient, but not multilocus heterozygosity, detected evidence of inbreeding depression for morphological traits. The relevance of these findings to the causes of heterozygosity--fitness correlations is discussed and predictions for other wild and captive populations are presented.

Animals↗
PubMed2005

Inbreeding depression in self-incompatible and self-compatible populations of Leavenworthia alabamica.

Inbreeding depression is one of the leading factors preventing the evolution of self-fertilization in plants. In populations where self-fertilization evolves, theory suggests that natural selection against partially recessive deleterious alleles will reduce inbreeding depression. The purpose of this study was to evaluate this hypothesis by comparing the magnitude of inbreeding depression in self-incompatible and self-compatible populations of Leavenworthia alabamica. Within-population crosses were conducted to compare the quantity and quality of offspring produced by outcrossing and self-fertilization. These progeny were grown in a common greenhouse and inbreeding depression was measured in germination, survival, biomass, transition rate to flowering, flower number, petal length, pollen grains/anther, pollen viability, and ovule number. In comparison to outcrossing, self-fertilization led to the production of fewer and smaller seeds within self-incompatible populations. Moreover, inbreeding depression was observed in eight of 11 offspring traits within self-incompatible populations of L. alabamica. In contrast, there was significant inbreeding depression only in flower number within self-compatible populations. The results of this study are consistent with the idea that self-fertilization selectively removes partially recessive deleterious alleles causing inbreeding depression in natural plant populations. However, in plant species such as L. alabamica where self-compatibility may evolve in small populations following long-distance dispersal, declines in inbreeding depression may also be facilitated by genetic drift.

Alabama↗
PubMed1999

Inbreeding depression in the wild.

Despite its practical application in conservation biology and evolutionary theory, the cost of inbreeding in natural populations of plants and animals remains to a large degree unknown. In this review we have gathered estimates of inbreeding depression (delta) from the literature for wild species monitored in the field. We have also corrected estimates of delta by dividing by F (coefficient of inbreeding), to take into account the influence that the variation in F will have on delta. Our data set includes seven bird species, nine mammal species, four species of poikilotherms (snakes, fish and snails) and 15 plant species. In total we obtained 169 estimates of inbreeding depression for 137 traits; 81 of those estimates included estimates of F. We compared our mammalian data (limited to those traits related to juvenile mortality) to the estimates for captive zoo species published by Ralls et al. (1988) to determine if, as predicted from the literature, natural estimates of inbreeding depression are higher than captive estimates. The mean delta +/- SE (significantly different from zero and not corrected for F ) for homeotherms was 0.509 +/- 0.081; for poikilotherms, 0.201 +/- 0.039; and for plants, 0.331 +/- 0.038. Levels of inbreeding depression this high in magnitude will be biologically important under natural conditions. When we limited our data set to mortality traits for mammals and corrected for F=0.25 (as is the case for the Ralls et al. data set), we found a significant difference between the two data sets; wild estimates had a substantially higher mean cost of inbreeding at F = 0.25: 2.155 (captive species: 0.314). Of the 169 estimates of delta, 90 were significantly different from zero, indicating that inbred wild species measured under natural conditions frequently exhibit moderate to high levels of inbreeding depression in fitness traits.

Animals↗
PubMed2000

A comparative study of ejaculate traits in three endangered ungulates with different levels of inbreeding: fluctuating asymmetry as an indicator of reproductive and genetic stress.

We studied three closely related species of endangered gazelles (Gazella dorcas, Gazella dama and Gazella cuvieri) with different levels of inbreeding in order to determine at which intensities inbreeding influences ejaculate traits. We also examined whether fluctuating asymmetry (FA) is a reliable indicator of genetic as well as reproductive stress. Our results show that, within each population, the individual coefficient of inbreeding is inversely related to ejaculate quality only in the species with the highest levels of inbreeding (G. cuvieri). In addition, FA is a reliable indicator of individual levels of inbreeding in both the species with the highest levels of inbreeding (G. cuvieri) and the species with intermediate levels of inbreeding (G. dama). Thus, FA appears in individuals whose levels of inbreeding are still not high enough to affect male reproductive potential and should therefore be considered a sensitive indicator of genetic stress. Finally, FA is also a reliable indicator of male reproductive stress since it is related to individual semen quality in all the species studied.

Animals↗
PubMed2003

Inbreeding depresses immune response in song sparrows (Melospiza melodia): direct and inter-generational effects.

A thorough knowledge of relationships between host genotype and immunity to parasitic infection is required to understand parasite-mediated mechanisms of genetic and population change. It has been suggested that immunity may decline with inbreeding. However, the relationship between inbreeding level and a host's response to a novel immune challenge has not been investigated in a natural population. We used the pedigreed population of song sparrows (Melospiza melodia) inhabiting Mandarte Island, Canada, to test the hypothesis that a sparrow's cell-mediated immune response (CMI) to an experimental challenge would decline with individual or parental inbreeding. CMI in 6-day-old chicks declined significantly with their mother's coefficient of inbreeding, demonstrating an inter-generational effect of maternal inbreeding on offspring immunity. In fledged juveniles and adult sparrows, CMI declined markedly with an individual's own coefficient of inbreeding, but not its mother's. This relationship was consistent across seasons, and was not attributable solely to heterosis in offspring of immigrant breeders. CMI also declined with age and increased with body condition in adult sparrows, but inbreeding explained 37% of the total variation. We emphasize the implications of this dramatic inbreeding depression in cell-mediated immunity for theories of parasite-mediated evolution and the susceptibility of small, inbred populations.

Animals↗
PubMed2004

Sex-specific, counteracting responses to inbreeding in a bird.

Inbreeding often depresses offspring fitness. Because females invest more than males in a reproductive event, inbreeding is expected to be more costly to mothers than fathers, creating a divergence between the reproductive interests of each sex and promoting sex-specific inbreeding strategies. Males and females may bias the probability of inbreeding by selecting copulation partners, and, in sexually promiscuous species, through male strategic sperm investment in different females and female selection of the sperm of different males. However, these processes are often difficult to study, and the way that different male and female strategies interact to determine inbreeding remains poorly understood. Here we demonstrate sex-specific, counteracting responses to inbreeding in the promiscuous red junglefowl, Gallus gallus. First, a male was just as likely to copulate with his full-sib sister as with an unrelated female. In addition, males displayed a tendency to: (i) initiate copulation faster when exposed to an unrelated female than when exposed to a sister, and (ii) inseminate more sperm into sisters than into unrelated females. Second, females retained fewer sperm following insemination by brothers, thus reducing the risk of inbreeding and counteracting male inbreeding strategies.

Animals↗
PubMed2004

Inbreeding in the Seychelles warbler: environment-dependent maternal effects.

The deleterious effects of inbreeding can be substantial in wild populations and mechanisms to avoid such matings have evolved in many organisms. In situations where social mate choice is restricted, extrapair paternity may be a strategy used by females to avoid inbreeding and increase offspring heterozygosity. In the cooperatively breeding Seychelles warbler, Acrocephalus sechellensis, neither social nor extrapair mate choice was used to avoid inbreeding facultatively, and close inbreeding occurred in approximately 5% of matings. However, a higher frequency of extra-group paternity may be selected for in female subordinates because this did reduce the frequency of mating between close relatives. Inbreeding resulted in reduced individual heterozygosity, which, against expectation, had an almost significant (P = 0.052), positive effect on survival. Conversely, low heterozygosity in the genetic mother was linked to reduced offspring survival, and the magnitude of this intergenerational inbreeding depression effect was environment-dependent. Because we controlled for genetic effects and most environmental effects (through the experimental cross-fostering of nestlings), we conclude that the reduced survival was a result of maternal effects. Our results show that inbreeding can have complicated effects even within a genetic bottlenecked population where the "purging" of recessive alleles is expected to reduce the effects of inbreeding depression.

Animals↗
PubMed2006

Life history correlates of inbreeding depression in mandrills (Mandrillus sphinx).

Inbreeding depression reflects the negative consequences of increased homozygosity at genes that affect fitness. We investigate inbreeding depression in a semi-free-ranging colony of mandrills (Mandrillus sphinx), using high-quality pedigree data, comprising five maternal generations and 20 years of morphological and demographic data. We examine the relationship between inbreeding coefficients and four fitness correlates: two growth parameters (mass and height for age) and longevity in both sexes, and age at first conception in females. Inbreeding was correlated with both growth parameters, but only in females, with inbred females being smaller than noninbred females. Inbreeding was also correlated significantly with age at first conception, with inbred females giving birth earlier in life than noninbred females. We suggest that sex-biased maternal investment may explain this sex-differential response to inbreeding, although the lack of a significant association between inbreeding and growth in males may also be due to the provisioned nature of the colony. The surprising relationship between age at first conception and inbreeding may be related to smaller adult size in inbred females, or to their being less able to escape from male sexual coercion.

Age Factors↗
PubMed2007

Inbreeding depression in an autotetraploid herb: a three cohort field study.

Autotetraploids are predicted to have reduced inbreeding depression relative to diploids. However, recent theory and information on genomic changes following autopolyploidy suggest that inbreeding depression may be closer to diploids. In three consecutive years, self and outcross pollinations were conducted on autotetraploid Campanulastrum americanum, seeds were planted into native sites, and biennial offspring were followed through seed production. Inbred individuals had lower germination rates, reduced survival, were smaller, and flowered later, producing fewer fruits with fewer seeds. Inbred offspring had 6% of the cumulative fitness of outcross offspring. Although performance varied substantially among cohorts, inbreeding depression for cumulative fitness was relatively constant, with delta ranging only from 0.92 to 0.95. C. americanum, like many outcrossing species, expressed very high amounts of inbreeding depression. This supports the hypothesis that inbreeding depression of some autotetraploids may be similar to that of diploids. Furthermore, few studies have measured temporal variation in inbreeding depression. Constant inbreeding depression given a sixfold range in cohort performance suggests that inbreeding depression may be relatively robust to environmental variation experienced by natural populations.

Campanulaceae↗
PubMed2006

The genetic architecture of life span and mortality rates: gender and species differences in inbreeding load of two seed-feeding beetles.

We examine the inbreeding load for adult life span and mortality rates of two seed beetle species, Callosobruchus maculatus and Stator limbatus. Inbreeding load differs substantially between males and females in both study populations of C. maculatus--life span of inbred females was 9-13% shorter than the life span of outbred females, whereas the life span of inbred males did not differ from the life span of outbred males. The effect of inbreeding on female life span was largely due to an increase in the slope of the mortality curve. In contrast, inbreeding had only a small effect on the life span of S. limbatus--life spans of inbred beetles were approximately 5% shorter than those of outbred beetles, and there was no difference in inbreeding load between the sexes. The inbreeding load for mean life span was approximately 0.4-0.6 lethal equivalents per haploid gamete for female C. maculatus and approximately 0.2-0.3 for both males and females of S. limbatus, all within the range of estimates commonly obtained for Drosophila. However, contrary to the predictions of mutation-accumulation models, inbreeding load for loci affecting mortality rates did not increase with age in either species, despite an effect of inbreeding on the initial rate of increase in mortality. This was because mortality rates decelerated with age and converged to a mortality plateau for both outbred and inbred beetles.

Animals↗