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Effects of inbreeding on skeletal development of Rattus villosissimus.

In a species of Australian native rat, Rattus villosissimus, which experiences extreme population fluctuations and possibly episodes of local inbreeding in the wild, generations of inbreeding in a laboratory colony led to altered skull shape and increased fluctuating asymmetry in some skeletal characters. Although inbreeding was closely associated with the number of generations in captivity, the effect of inbreeding after controlling statistically for the generation number was to decrease skull length and width. The effect of generations in captivity after controlling for inbreeding was to increase skull length and width. The joint effect of these confounded determinants was to produce rats with increasingly broad and short skulls through generations of inbreeding. Developmental anomalies of the incisors and feet appeared in the population. The average effects of inbreeding on fluctuating asymmetry were not strong, as most inbred and noninbred rats were not detectably asymmetric. Asymmetry appeared to be a threshold phenomenon, as significantly asymmetric animals were more prevalent among the more highly inbred rats of later generations. We detected no trend for a lessening impact of inbreeding after many generations, as would have been expected if selection had been purging the population of its genetic load. Individual heterozygosity across five polymorphic allozyme loci was correlated with size and asymmetry metrics, but only in so far as could be accounted for by the correlation of sample heterozygosity with the level of inbreeding and the effect of inbreeding on size and asymmetry.

Animals↗
PubMed2006

Inbreeding and endangered species management: is New Zealand out of step with the rest of the world?

There is growing evidence that inbreeding can negatively affect small, isolated populations. This contrasts with the perception in New Zealand, where it has been claimed that native birds are less affected by inbreeding depression than threatened species from continental regions. It has been argued that New Zealand's terrestrial birds have had a long history of small population size with frequent inbreeding and that this has 'purged" deleterious alleles. The rapid recovery of many tiny and inbred populations after introduced predators have been controlled, and without input from more genetically diverse populations, has further supported the view that inbreeding is not a problem. This has led to a general neglect of inbreeding as a factor in recovery programs for highly endangered species such as the Black Robin (Petroica traversi) and Kakapo (Strigops habroptilis). We examined the reasons for this situation and review the New Zealand evidence for genetic purging. Complete purging of the genetic load and elimination of inbreeding depression are unlikely to occur in natural populations, although partial purging may be more likely where small populations have become inbred over an extended period of time, such as on small isolated islands. Recent molecular data are consistent with the view that island endemics, including New Zealand's threatened birds, have low genetic variation and hence have possibly gone through longer periods of inbreeding than threatened species from continental regions. Nevertheless, results from recent field studies in New Zealand indicate that, despite the opportunity for purging, inbreeding depression is evident in many threatened species. Although inbreeding depression has not prevented some populations from recovering from severe bottlenecks, the long-term consequences of inbreeding and small population size--the loss of genetic variation--are potentially much more insidious. The degrees to which genetic factors reduce population viability generally remain unquantified in New Zealand. Although minimizing ecological risks (e.g., preventing reinvasion of islands by mammalian predators) will continue to receive high priority in New Zealand because of their much larger impacts, we advocate that genetic considerations be better integrated into recovery plans.

Animals↗
PubMed2006

Udder health shows inbreeding depression in Danish Holsteins.

The purpose of this study was to estimate inbreeding depression for udder health using records on mastitis incidence and somatic cell count (SCC). Data were selected based on a pedigree completeness index so that inbreeding coefficients were reliable. Average inbreeding was 3.3%. The presence or absence of mastitis was considered in first (CM1), second (CM2), and third (CM3) lactations, and was recorded as a binary trait. Somatic cell count was also included and analyzed on the log scale. A minimum of 140,000 cows with records were included per trait. Linear sire models were used and (co)variance components were estimated. Linear and curvilinear effects of the coefficient of inbreeding were included. Inbreeding significantly affected all traits investigated. Three traits, CM1, CM3, and SCC, showed a nonlinear relationship between phenotype and inbreeding coefficient. A cow with 5% inbreeding compared with a cow with 2% inbreeding had a higher SCC and a higher incidence of mastitis. The SCC increased by 1,500 cells/mL in first lactation and the incidence of mastitis increased by 1.08, 0.55, and 0.98% in first, second, and third lactation, respectively. The corresponding reduction in net return from these traits over 3 lactations amounted to 11.00 US dollars under Danish production circumstances. These results are a step on the way to estimating the total cost of inbreeding depression to determine an acceptable rate of inbreeding.

Animals↗
PubMed1995

Calculation and use of inbreeding coefficients for genetic evaluation of United States dairy cattle.

Inbreeding coefficients are calculated routinely for all animals included in national genetic evaluations for yield traits. The base population for inbreeding is defined as animals born during 1960. Animals with unknown parents are assumed to have inbreeding coefficients that are equal to the mean of coefficients for animals with known parents born during the same year. Mean inbreeding coefficients reached .03 to .04 for recent years, and coefficients for some animals exceeded .50. The annual increase in level of inbreeding was highest for Milking Shorthorns, but the rate of change of that increase was greatest for Holsteins. Accounting for inbreeding in calculation of the inverse of the relationship matrix had only a small effect on evaluations. For Jersey, the maximum change in breeding value was 73 kg of milk for cows and 40 kg of milk for bulls with > or = 10 daughters. Estimates of inbreeding depression were similar across breeds for production traits and were -29.6 kg of milk, -1.08 kg of fat, and -.97 kg of protein per 1% of inbreeding for Holsteins. In January 1994, the USDA began considering the percentage of inbreeding when calculating inverses of relationship matrices, the largest matrix representing over 20 million Holsteins; this inbreeding percentage was released to the dairy industry for bulls.

Animals↗
PubMed1998

The effects of inbreeding on the lifetime performance of dairy cattle.

The effects of inbreeding on the lifetime performance of dairy cattle were examined using data for production, somatic cell score, and linear type for all Holstein cows that were scored between 1983 and 1993. The results of fixed and mixed animal models differed. Relative net income adjusted for opportunity cost for the 2,610,123 cows with an 84-mo opportunity for herdlife was depressed by $14.79 for fluid market pricing and by $12.40 for manufacturing pricing per 1% increase in inbreeding. Mixed model estimates of depression per 1% of increase in inbreeding were +0.55 d for age at first calving, -6 d for days of productive life, and -4.8 for days in milk. Inbreeding decreased the mature equivalent production of milk, fat, and protein during first lactation by 27, 0.9, and 0.8 kg and the lifetime production of milk, fat, and protein by 177, 6.0, and 5.5 kg, respectively, per 1% increase in inbreeding. Inbreeding had little effect on conformation traits. The effects of inbreeding were cumulative, and effects on lifetime profit functions were relatively larger than the effects on lactation traits. Registered cows had higher levels of inbreeding and larger standard deviations than did grade cows. Inbreeding in registered cows depressed relative net income adjusted for opportunity cost for fluid and manufacturing prices by $24.43 and $21.78, respectively; income was depressed $9.43 and $9.02, respectively, for grade cows. The difference between registered and grade cattle is likely due to the incomplete pedigree information in grade animals. Inbreeding among cows in this study was not high on average, but economic losses represented a significant cost to the producer.

Animals↗
PubMed1999

Selection and mating considering expected inbreeding of future progeny.

Animals most related or least related to current members of their breed were revealed by calculating the expected inbreeding of their future progeny. A sample of potential mates was chosen by randomly selecting 600 females from a recent birth year (1995). Relationships among the sample were computed by the tabular method. Relationships of other animals to the sample population were computed quickly from the relationships of their parents or ancestors. To-Mar Blackstar-ET and Round Oak Rag Apple Elevation were most related to the Holstein breed with expected inbreeding of 7.9 and 7.7%, respectively. Corresponding Jersey bulls were Highland Magic Duncan and Soldierboy Boomer Sooner of CJF with expected inbreeding of 10.9 and 9.5%, respectively. The highest expected inbreeding was 11.1% for Selwood Bettys Commander, 8.6% for Forest Lawn Simon Jetway, 10.1% for Dutch Mill Telestars Fayette, and 7.4% for Korncrest Pacesetter for Ayrshire, Brown Swiss, Guernsey, and Milking Shorthorn breeds, respectively. Regression on inbreeding in the genetic evaluation model removed effects of past inbreeding. Future inbreeding effects could be included for each potential mating or by adjusting breeding values for average inbreeding expected with random mating. The correlation between Holstein breeding values unadjusted and adjusted for inbreeding was 0.9976. The estimated genetic trend was 6% lower with future inbreeding included.

Animals↗
PubMed2003

Inbreeding effects on lifetime in David's deer (Elaphurus davidianus, Milne Edwards 1866) population.

The current population of David's deer is derived from 18 individuals kept in Woburn Abbey Park (England). The aim of this study is to evaluate the inbreeding rate as well as inbreeding depression in longevity. The recorded data have been extracted from the International Species Information System (ISIS). Complete records of 2042 individuals (born in 1947-2000) from zoological gardens were studied. The following four subsets of data were formed: all individuals, individuals over 31 days of life, sexually mature individuals (above 450 days old) and individuals with identified sex. Two models (including inbreeding coefficient as linear and quadratic covariables, respectively) have been employed. These computations were performed by the use of the DFREML package programs. This study has shown that average levels of inbreeding in the David's deer are relatively low (no exceed 0.028). The highest level of inbreeding was registered for mature individuals. In general, the average inbreeding on length of life was small for the above mentioned the inbreeding level (from 24 days to 77 days). However, on the basis estimated regression coefficients it can be suggested that an increase of inbreeding could lead to a drastic reduction of longevity. Relationships between inbreeding level and longevity are usually better described by quadratic partial regression (except for the oldest individuals). On the other hand, from a statistical point of view, a relatively low inbreeding level of the population studied is not suitable to derive the slope of the dependencies.

Animals↗
PubMed2025

Inbreeding load in finite populations from dominant and overdominant mutations.

Inbreeding depression is a widespread phenomenon that reflects the burden of deleterious effects hidden in heterozygosis in non-inbred populations but exposed in homozygosis in inbred individuals, known as inbreeding load (B). This load can be due to partially or fully recessive deleterious mutations (dominance model) or to heterozygote advantage (overdominance model, where both homozygotes are deleterious relative to the heterozygote). There are many studies addressing the changes in inbreeding load in finite populations assuming the dominance model. However, the contribution of overdominance to inbreeding depression has been focused on infinite-size populations. We carried out computer simulations to investigate the joint impact of dominant and pure overdominant mutations on inbreeding load, both for self-fertilizing populations and for panmictic populations suffering from a drastic bottleneck. We found that the overdominant inbreeding load can be substantially reduced by drift even for symmetrical overdominance, at least when considering mutations of small effect. For panmictic bottlenecked populations, the reduction in inbreeding load under dominance and overdominance loci cannot be easily distinguished. However, while purging depletes inbreeding load from dominant loci, slowing inbreeding depression and leading to partial fitness recovery, for overdominant loci fitness declines monotonically.

Inbreeding↗
PubMed2000

A study of contemporary levels and temporal trends in inbreeding in the Tangier Island, Virginia, population using pedigree data and isonymy.

In this study we describe inbreeding in a large pedigree from Tangier Island, Virginia, in which we compare two commonly used methods to estimate inbreeding in humans: pedigree and isonymy (identical surnames of spouses). Genealogical data on 3,512 individuals dating back to 1722 were used. Using the pedigree method, we determined an average inbreeding coefficient (F) of 0.00873 for the community as a whole, and 0.018 for inbred individuals. Analysis of temporal trends showed that inbreeding began around 1800 and peaked at 0.0109 in 1824-1849 and 1875-1899. Thereafter, inbreeding steadily declined to 0.00565 in 1975-1997. Analysis of pedigree structure complexity over time showed that close consanguinity contributes to inbreeding in the earlier cohorts, and remote consanguinity accounts for much of the inbreeding in the later cohorts. The number of common ancestors increases over time, as does the number of paths connecting inbred individuals to these common ancestors. Inbreeding estimates based on the isonymy approach yielded a 2.2-fold higher value of F (0.01945) compared to the pedigree method. Total isonymy estimates over 25-year cohorts overestimated inbreeding values from pedigree data between 1. 5-8-fold. We speculate that the overestimation is probably due to the inability of our data to satisfy the method's assumption of monophyletic origin of each surname. In conclusion, inbreeding in the Tangier Island population is consistent with the isolated nature of its population, and temporal trends reflect patterns in emigration and a breakdown in isolation over time.

Adolescent↗
PubMed1988

Inbreeding and genetic disease in Sottunga, Finland.

The contribution of inbreeding to the prevalence of recessive genetic diseases in the Aland Island parish of Sottunga is investigated. Genealogical data for 3,030 individuals spanning up to 15 generations were used to estimate inbreeding. This small island community shows a low average inbreeding value of .0031 for the period 1725-1975. A cohort analysis shows that inbreeding increased from 1750 to 1900, when maximum inbreeding for those born in Sottunga reached .0057. A sharp decline in inbreeding occurred thereafter. Individuals with island-born parents made the largest contributions to inbreeding in all time periods compared to those with one or two migrant parents. These trends are consistent with changing migration patterns and isolate breakdown in Aland since 1900. An analysis of pedigree development demonstrates that remote consanguinity contributed more to inbreeding through time than close consanguinity. Both the number of common ancestors and the number of paths of relationship between spouses increased dramatically through time, the latter at a much faster rate. The contribution to average inbreeding per path, however, diminished rapidly through time. This analysis indicates that inbreeding does not account for the high incidence of autosomal recessive disorders, such as tapetoretinal disease, found in the parish.

Consanguinity↗
PubMed1991

Effects of a change in the level of inbreeding on the genetic load.

"The effects of inbreeding may not be as noticeable in the first generation as the invigoration immediately apparent after crossing". This statement, published in 1919, has received little attention, and has apparently never been tested empirically, although the reduction of the genetic load of populations by inbreeding is well known in theoretical terms. Because inbreeding increases homozygosity, and hence the effectiveness of selection against recessive or partially recessive detrimental alleles, changes in levels of inbreeding can lead to a reduction in the frequencies of such mutant alleles. This results in equilibration at higher population mean fitness and is referred to as 'purging' populations of their genetic load. Severe inbreeding can also reduce genetic load due to overdominant alleles, provided selection coefficients are not symmetrical at all loci, because alleles giving lower fitness will be reduced in frequency at equilibrium. With either fitness model, however, reduction in genetic load takes time, and the initial effect of an increase in inbreeding is reduced fitness due to homozygosity. There are few data relating to the extent to which fitness is reduced during inbreeding in a set of lines and to how long the reduction lasts before increasing again to the initial level, or higher. Inbreeding experiments involving sib mating in mice and Drosophila subobscura, and successive bottlenecks in house flies have yielded some evidence consistent with the purging hypothesis. Here, we report results of an experiment demonstrating a prolonged time-course of recovery of mean fitness under self-fertilization of a naturally outcrossing plant, and also compare our results with expectations derived by computer calculations. Our results show that the genetic load present in an outcrossing population can be explained only with a high mutation rate to partially recessive deleterious alleles, and that inbreeding purges the population of mutant alleles.

Animals↗
PubMed2000

Inbreeding depression and mating systems in two species of Linanthus (Polemoniaceae).

Theory predicts that, at equilibrium, the magnitude of inbreeding depression caused by recessive alleles should decrease as the level of self-fertilization increases, facilitating the evolution of even higher selfing rates. Data are presented on mating systems and inbreeding depression in multiple populations of two annual species in the genus Linanthus (Polemoniaceae). Outcrossing rates were found to be less than 0.075 in populations of a small-flowered species, L. bicolor, and ranged from 0.104 to 0.300 in populations of a larger-flowered species, L. jepsonii. Inbreeding depression for both species was low for all life history stages, with cumulative inbreeding depression less than 0.23 in all populations. Significant inbreeding depression for pollen fertility was found in L. jepsonii populations and may contribute substantially to total inbreeding depression. A competitive treatment had no significant effect on the expression of inbreeding depression for above-ground dry mass. In accordance with theoretical expectations, the magnitude of inbreeding depression was lower in L. bicolor, the more highly selfing species. The magnitude of inbreeding depression in L. jepsonii, although greater than that of L. bicolor, is not sufficient to prevent evolution of increased selfing rates in this species, according to some theoretical models of mating system evolution.

Analysis of Variance↗
PubMed2000

Equivalent inbreeding depression under laboratory and field conditions in a tree-hole-breeding mosquito.

Understanding the consequences of inbreeding has important implications for a wide variety of topics in population biology. However, most studies quantifying the effects of inbreeding are performed under artificial farm, greenhouse, laboratory or zoo conditions. Although several authors have argued that the deleterious effects of inbreeding (inbreeding depression) are likely to be more severe under natural field conditions than in artificial experimental environments, these arguments are usually speculative or based on indirect comparisons. We quantified the effects of inbreeding on fitness traits in a tree-hole-breeding mosquito Aedes geniculatus) under near-optimal laboratory conditions and in three natural tree holes. Our index of fitness (Ro) was lower in the field than in the laboratory and declined due to inbreeding in both However, environments, we found no significant interactions between inbreeding depression and environmental conditions. In both the field and laboratory a 10% increase in the inbreeding coefflicient (F) led to a 12-15) decline in fitness (Ro) These results suggest that inbreeding depression will not necessarily be more extreme under natural field conditions than in the laboratory.

Aedes↗
PubMed2002

Severe inbreeding depression in collared flycatchers (Ficedula albicollis).

The causes and magnitude of inbreeding depression are of considerable importance for a wide range of issues in evolutionary and conservation biology, but we have only a limited understanding of inbreeding depression in natural populations. Here, we present a study of inbreeding in a large wild population of collared flycatchers (Ficedula albicollis). Inbreeding was rare, to the extent that we detected only 1.04% of 2139 matings over 18 years that resulted in offspring with a non-zero inbreeding coefficient, f > 0. When it did occur, inbreeding caused a significant reduction in the egg-hatching rate, in fledgling skeletal size and in post-fledging juvenile survival, with the number of offspring being recruited to the breeding population from a nest of f = 0.25 being reduced by 94% relative to a non-inbred nest. A maximum-likelihood estimate of the number of lethal equivalents per gamete was very high at B = 7.47, indicating a substantial genetic load in this population. There was also a non-significant tendency for inbreeding depression to increase with the strength of selection on a trait. The probability of mating between close relatives (f = 0.25) increased throughout the breeding season, possibly reflecting increased costs of inbreeding avoidance. Our results illustrate how severe inbreeding depression and considerable genetic load may exist in natural populations, but detecting them may require extensive long-term datasets.

Animals↗
PubMed2000

An association between a floral trait and inbreeding depression.

Inbreeding depression is a general phenomenon that is well documented in many plants and animals. Furthermore, it is generally considered to be the driving force behind mating-system evolution. Traditionally, the focus has been on the mean level of inbreeding depression in populations. However, more recently, the variation in inbreeding depression among individuals within populations has been shown to be influential in mating-system evolution. One set of theories predicts that genetic associations will develop between a mating-system locus and loci causing inbreeding depression, whereas another suggests either that no such association will occur or that it will be difficult to detect empirically. Here, we focus on variation in inbreeding depression among individuals and present empirical evidence of a genetic association between genes causing inbreeding depression and a floral trait influencing the mating system (i.e., selfing rate). We found a positive association between inbreeding depression and herkogamy (the degree to which the stigma and anthers are separated) in an annual plant, Gilia achilleifolia. These results are consistent with theory predicting that an individual's history of inbreeding will affect its level of inbreeding depression and highlight the potential importance of genetic associations between selfing-modifier traits and viability in mating-system evolution.

California↗
PubMed2000

Maintenance of androdioecy in the freshwater shrimp, Eulimnadia texana: estimates of inbreeding depression in two populations.

Androdioecy is an uncommon form of reproduction in which males coexist with hermaphrodites. Androdioecy is thought to be difficult to evolve in species that regularly inbreed. The freshwater shrimp Eulimnadia texana has recently been described as both androdioecious and highly selfing and is thus anomalous. Inbreeding depression is one factor that may maintain males in these populations. Here we examine the extent of "late" inbreeding depression (after sexual maturity) in these clam shrimp using two tests: (1) comparing the fitness of shrimp varying in their levels of individual heterozygosity from two natural populations that differ in overall genetic diversity; and (2) specifically outcrossing and selfing shrimp from these same populations and comparing fitness of the resulting offspring. The effects of inbreeding differed within each population. In the more genetically diverse population, fecundity, size, and mortality were significantly reduced in inbred shrimp. In the less genetically diverse population, none of the fitness measures was significantly lowered in selfed shrimp. Combining estimates of early inbreeding depression from a previous study with current estimates of late inbreeding depression suggests that inbreeding depression is substantial (delta = 0.68) in the more diverse population and somewhat lower (delta = 0.50) in the less diverse population. However, given that males have higher mortality rates than hermaphrodites, neither estimate of inbreeding depression is large enough to account for the maintenance of males in either population by inbreeding depression alone. Thus, the stability of androdioecy in this system is likely only if hermaphrodites are unable to self-fertilize many of their own eggs when not mated to a male or if male mating success is generally high (or at least high when males are rare). Patterns of fitness responses in the two populations were consistent with the hypothesis that inbreeding depression is caused by partially recessive deleterious alleles, although a formal test of this hypothesis still needs to be conducted.

Animals↗
PubMed2003

Inbreeding depression and haplodiploidy: experimental measures in a parasitoid and comparisons across diploid and haplodiploid insect taxa.

It has long been assumed that inbreeding depression in haplodiploid organisms is low due to their ability to purge genetic load in haploid males. It has been suggested that this low genetic load could facilitate the evolution of inbreeding behaviors driven by local mate competition in hymenopteran parasitoids. I have examined inbreeding depression in haplodiploids in two ways. First I show that an outbreeding haplodiploid wasp Uscana semifumipennis (Hymenoptera: Trichogrammatidae) suffers substantial inbreeding depression. Longevity was 38% shorter, fecundity was 32% lower, and sex ratio was 5% more male for experimentally inbred wasps when compared to outbred controls. There were interactions between size and both fecundity and sex ratio for inbred wasps that were not seen for outbred individuals. Second, an analysis of data from the literature suggests that when inbreeding is experimentally imposed on populations, haplodiploid insects and mites as a group do suffer less from inbreeding depression than diploid insects, although substantial inbreeding depression in haplodiploid taxa does exist. The meta-analysis revealed no difference in inbreeding depression between gregarious haplodiploid wasps, which are likely to have a history of inbreeding, and solitary haplodiploid species, which are assumed to be primarily outbred.

Analysis of Variance↗
PubMed2005

Heterozygosity, inbreeding and neonatal traits in Soay sheep on St Kilda.

We investigated whether birth weight and neonatal survival, a period within which 24% of all mortalities occur, were correlated with levels of inbreeding in St Kilda Soay sheep, using pedigree inbreeding coefficients and four marker-based estimators of inbreeding. None of the inbreeding estimators, either of the offspring, or of their mothers, explained significant variation in a lamb's birth weight or probability of surviving the neonatal period, suggesting low inbreeding depression for these traits. We evaluated the correlation between the marker-based measures of inbreeding and inbreeding coefficients obtained from the Soay pedigree, where paternal links were inferred using the same panel of microsatellite markers. Even when using a relatively complete portion of the pedigree, in which all individuals had known maternal and paternal grandparents, the correlation was found to be weak (r = -0.207, where mean f = 0.0168). These results add support to the recent prediction that when the mean and variance in inbreeding are low in a population, heterozygosity-fitness correlations can be very weak or even undetectable. The pursuit of more detailed pedigrees offers the best prospect for identifying inbreeding depression within this study population.

Animals↗