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At least 19 recordsLinked to original sources
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↗
PubMed2005

A genetic interpretation of the variation in inbreeding depression.

Inbreeding depression is expected to play an important but complicated role in evolution. If we are to understand the evolution of inbreeding depression (i.e., purging), we need quantitative genetic interpretations of its variation. We introduce an experimental design in which sires are mated to multiple dams, some of which are unrelated to the sire but others are genetically related owing to an arbitrary number of prior generations of selfing or sib-mating. In this way we introduce the concept of "inbreeding depression effect variance," a parameter more relevant to selection and the purging of inbreeding depression than previous measures. We develop an approach for interpreting the genetic basis of the variation in inbreeding depression by: (1) predicting the variation in inbreeding depression given arbitrary initial genetic variance and (2) estimating genetic variance components given half-sib covariances estimated by our experimental design. As quantitative predictions of selection depend upon understanding genetic variation, our approach reveals the important difference between how inbreeding depression is measured experimentally and how it is viewed by selection.

Analysis of Variance↗
PubMed2006

Selection and inbreeding depression: effects of inbreeding rate and inbreeding environment.

The magnitude of inbreeding depression in small populations may depend on the effectiveness with which natural selection purges deleterious recessive alleles from populations during inbreeding. The effectiveness of this purging process, however, may be influenced by the rate of inbreeding and the environment in which inbreeding occurs. Although some experimental studies have examined these factors individually, no study has examined their joint effect or potential interaction. In the present study, therefore, we performed an experiment in which 180 lineages of Drosophila melanogaster were inbred at slow and fast inbreeding rates within each of three inbreeding environments (benign, high temperature, and competitive). The fitness of all lineages was then measured in a common benign environment. Although slow inbreeding reduced inbreeding depression in lineages inbred under high temperature stress, a similar reduction was not observed with respect to the benign or competitive treatments. Overall, therefore, the effect of inbreeding rate was nonsignificant. The inbreeding environment, in contrast, had a larger and more consistent effect on inbreeding depression. Under both slow and fast rates of inbreeding, inbreeding depression was significantly reduced in lineages inbred in the presence of a competitor D. melanogaster strain. A similar reduction of inbreeding depression occurred in lineages inbred under high temperature stress at a slow inbreeding rate. Overall, our findings show that inbreeding depression is reduced when inbreeding takes place in a stressful environment, possibly due to more effective purging under such conditions.

Animals↗
PubMed2005

Outbreeding depression, but no inbreeding depression in haplodiploid Ambrosia beetles with regular sibling mating.

In sexual reproduction the genetic similarity or dissimilarity between mates strongly affects offspring fitness. When mating partners are too closely related, increased homozygosity generally causes inbreeding depression, whereas crossing between too distantly related individuals may disrupt local adaptations or coadaptations within the genome and result in outbreeding depression. The optimal degree of inbreeding or outbreeding depends on population structure. A long history of inbreeding is expected to reduce inbreeding depression due to purging of deleterious alleles, and to promote outbreeding depression because of increased genetic variation between lineages. Ambrosia beetles (Xyleborini) are bark beetles with haplodiploid sex determination, strong local mate competition due to regular sibling mating within the natal chamber, and heavily biased sex ratios. We experimentally mated females of Xylosandrus germanus to brothers and unrelated males and measured offspring fitness. Inbred matings did not produce offspring with reduced fitness in any of the examined life-history traits. In contrast, outcrossed offspring suffered from reduced hatching rates. Reduction in inbreeding depression is usually attributed to purging of deleterious alleles, and the absence of inbreeding depression in X. germanus may represent the highest degree of purging of all examined species so far. Outbreeding depression within the same population has previously only been reported from plants. The causes and consequences of our findings are discussed with respect to mating strategies, sex ratios, and speciation in this unusual system.

Analysis of Variance↗
PubMed1995

Individual variation in inbreeding depression: the roles of inbreeding history and mutation.

We use mutation-selection recursion models to evaluate the relative contributions of mutation and inbreeding history to variation among individuals in inbreeding depression and the ability of experiments to detect associations between individual inbreeding depression and mating system genotypes within populations. Poisson mutation to deleterious additive or recessive alleles generally produces far more variation among individuals in inbreeding depression than variation in history of inbreeding, regardless of selfing rate. Moreover, variation in inbreeding depression can be higher in a completely outcrossing or selfing population than in a mixed-mating population. In an initially random mating population, the spread of a dominant selfing modifier with no pleiotropic effects on male outcross success causes a measurable increase in inbreeding depression variation if its selfing rate is large and inbreeding depression is caused by recessive lethals. This increase is observable during a short period as the modifier spreads rapidly to fixation. If the modifier alters selfing rate only slightly, it fails to spread or causes no measurable increase in inbreeding depression variance. These results suggest that genetic associations between mating loci and inbreeding depression loci could be difficult to demonstrate within populations and observable only transiently during rapid evolution to a substantially new selfing rate.

Animals↗
PubMed2006

Reduced inbreeding depression due to historical inbreeding in Drosophila melanogaster: evidence for purging.

An important issue in conservation biology and the study of evolution is the extent to which inbreeding depression can be reduced or reversed by natural selection. If the deleterious recessive alleles causing inbreeding depression can be 'purged' by natural selection, outbred populations that have a history of inbreeding are expected to be less susceptible to inbreeding depression. This expectation, however, has not been realized in previous laboratory experiments. In the present study, we used Drosophila melanogaster as a model system to test for an association between inbreeding history and inbreeding depression. We created six 'purged' populations from experimental lineages that had been maintained at a population size of 10 male-female pairs for 19 generations. We then measured the inbreeding depression that resulted from one generation of full-sib mating in the purged populations and in the original base population. The magnitude of inbreeding depression in the purged populations was approximately one-third of that observed in the original base population. In contrast to previous laboratory experiments, therefore, we found that inbreeding depression was reduced in populations that have a history of inbreeding. The large purging effects observed in this study may be attributable to the rate of historical inbreeding examined, which was slower than that considered in previous experiments.

Alleles↗
PubMedDate not supplied

Ancestral inbreeding only minimally affects inbreeding depression in mammalian populations.

Inbreeding depression can be reduced, or purged, by selection against deleterious alleles. This prediction is the basis of the recommendation that captive wildlife populations suffering from inbreeding depression be intentionally bred from healthy inbred animals. Yet data on the effectiveness of purging inbreeding depression are few. In this study I present and use two different regression models (an ancestral inbreeding model and a lethal recessive model) to test for the presence of purging effects in 25 captive mammalian populations. Fitness components examined were neonatal survival, survival from neonate to weaning, and litter size. In only one species was purging statistically significant. However, 15 of 17 species that showed inbreeding depression exhibited a slight decline in inbreeding depression in neonatal survival among descendants of inbred animals. These results show a small but highly significant trend of purging on neonatal survival. No trends in purging effects were observed in weaning survival or litter size. The effects were not likely to be strong enough to be of practical use in eliminating inbreeding depression.

Animals↗
PubMed2005

A simulation study on detecting purging of inbreeding depression in captive populations.

Inbreeding depression threatens the survival of small populations of both captive and wild outbreeding species. In order to fully understand this threat, it is necessary to investigate what role purging plays in reducing inbreeding depression. Ballou (1997) undertook such an investigation on 25 mammalian populations, using an ancestral inbreeding regression model to detect purging. He concluded that there was a small but highly significant trend of purging on neonatal survival across the populations. We tested the performance of the regression model that Ballou used to detect purging on independently simulated data. We found that the model has low statistical power when inbreeding depression is caused by the build-up of mildly deleterious alleles. It is therefore possible that Ballou's study may have underestimated the effects of ancestral inbreeding on the purging of inbreeding depression in captive populations if their inbreeding depression was caused mainly by mildly deleterious mutations. We also developed an alternative regression model to Ballou's, which showed an improvement in the detection of purging of mildly deleterious alleles but performed less well if deleterious alleles were of a large effect.

Alleles↗
PubMed2003

Environment-dependent inbreeding depression in a hermaphroditic freshwater snail.

Inbreeding depression was simultaneously studied under contrasted environments, laboratory and natural conditions, using individuals originating from 14 families of the freshwater snail Physa acuta. Both survival and growth of juveniles showed inbreeding depression under laboratory conditions. The same fitness components were monitored with mature snails either kept under laboratory conditions or released at a natural site and analysed using capture-mark-recapture models. Genetic composition of both samples was similar. Inbreeding depression on survival was highest in the laboratory while strong outbreeding depression was revealed in the field. Thus inbreeding depression may not be always higher under natural conditions, at the opposite of what is commonly assumed. We suggest that inbreeding depression is dependent on metabolic requirements imposed by the environment. Other evidences showing that inbreeding depression is environment-dependent are reviewed. We conclude that genetic models should include both genetic and environmental variance in inbreeding depression for studying mating system evolution.

Adaptation, Physiological↗
PubMed2024

Detecting inbreeding depression in structured populations.

Measuring inbreeding and its consequences on fitness is central for many areas in biology including human genetics and the conservation of endangered species. However, there is no consensus on the best method, neither for quantification of inbreeding itself nor for the model to estimate its effect on specific traits. We simulated traits based on simulated genomes from a large pedigree and empirical whole-genome sequences of human data from populations with various sizes and structures (from the 1,000 Genomes project). We compare the ability of various inbreeding coefficients ([Formula: see text]) to quantify the strength of inbreeding depression: allele-sharing, two versions of the correlation of uniting gametes which differ in the weight they attribute to each locus and two identical-by-descent segments-based estimators. We also compare two models: the standard linear model and a linear mixed model (LMM) including a genetic relatedness matrix (GRM) as random effect to account for the nonindependence of observations. We find LMMs give better results in scenarios with population or family structure. Within the LMM, we compare three different GRMs and show that in homogeneous populations, there is little difference among the different [Formula: see text] and GRM for inbreeding depression quantification. However, as soon as a strong population or family structure is present, the strength of inbreeding depression can be most efficiently estimated only if i) the phenotypes are regressed on [Formula: see text] based on a weighted version of the correlation of uniting gametes, giving more weight to common alleles and ii) with the GRM obtained from an allele-sharing relatedness estimator.

Humans↗
PubMed1999

The contribution of male-sterility mutations to inbreeding depression in Mimulus guttatus.

The magnitude of inbreeding depression can influence many aspects of a population's ecology and evolution, including the nature of selection acting on the mating system and the chances that the population will go extinct during periods of small population size. If inbreeding depression is caused primarily by recessive mutations of large effect on fitness, such as lethals or steriles, then it is expected to be purged rapidly by selection with moderate amounts of inbreeding. In contrast, inbreeding depression primarily caused by many genes with mild effects on fitness will not be rapidly purged with inbreeding, so it should be a more resilient barrier to the evolution of self-fertilization and a more significant threat to the survival of endangered species. Here I show that recessive male-sterility alleles at individual loci are common in a primarily outcrossing population of the plant Mimulus guttatus. Despite the high frequency of these major mutations, most of the inbreeding depression for male fertility and cumulative measures of lifetime fitness results from more mildly deleterious alleles. Male-sterility alleles contribute to 31% of the inbreeding depression for the fraction of viable pollen grains, and to 26% of the inbreeding depression for total fitness. These results suggest that most of the inbreeding depression for male fertility in this population would not be purged, in the short term, with moderate inbreeding.

Alleles↗
PubMed2002

Environmental conditions affect the magnitude of inbreeding depression in survival of Darwin's finches.

Understanding the fitness consequences of inbreeding (inbreeding depression) is of importance to evolutionary and conservation biology. There is ample evidence for inbreeding depression in captivity, and data from wild populations are accumulating. However, we still lack a good quantitative understanding of inbreeding depression and what influences its magnitude in natural populations. Specifically, the relationship between the magnitude of inbreeding depression and environmental severity is unclear. We quantified inbreeding depression in survival and reproduction in populations of cactus finches (Geospiza scandens) and medium ground finches (Geospiza fortis) living on Isla Daphne Major in the Galápagos Archipelago. Our analyses showed that inbreeding strongly reduced the recruitment probability (probability of breeding given that an adult is alive) in both species. Additionally, in G. scandens, first-year survival of an offspring with f = 0.25 was reduced by 21% and adults with f = 0.25 experienced a 45% reduction in their annual probability of survival. The magnitude of inbreeding depression in both adult and juvenile survival of this species was strongly modified by two environmental conditions, food availability and number of competitors. In juveniles, inbreeding depression was only present in years with low food availability, and in adults inbreeding depression was five times more severe in years with low food availability and large population sizes. The combination of relatively severe inbreeding depression in survival and the reduced recruitment probability led to the fact that very few inbred G. scandens ever succeeded in breeding. Other than recruitment probability, no other trait showed evidence of inbreeding depression in G. fortis, probably for two reasons: a relatively high rate of extrapair paternity (20%), which may lead to an underestimate of the apparent inbreeding depression, and low sample sizes of highly inbred G. fortis, which leads to low statistical power. Using data from juvenile survival, we estimated the number of lethal equivalents carried by G. scandens, G. fortis, and another congener, G. magnirostris. These results suggest that substantial inbreeding depression can exist in insular populations of birds, and that the magnitude of the inbreeding depression is a function of environmental conditions.

Animals↗
PubMed1986

The interdependence of mating structure and inbreeding depression.

The level of inbreeding depression depends on the genetic structure and composition of a population, and is not a meaningful concept in its own right. Models are presented for the dynamics of alleles governing mating strategy when viability is determined by generalized heterosis or lethal recessive alleles. It is shown that a protected polymorphism for mating strategy may ensue from generalized heterosis, while lethal recessive alleles may favor the common mating strategy. Further, neither model provides the conditions allowing spread of an allele when rare (protection) which are obtained by assuming as constant the level of inbreeding depression associated with the equilibrium genetic structure dictated by the common mating strategy.

Animals↗
PubMed1999

Inbreeding depression and selfing rates in a self-compatible, hermaphroditic species, Schiedea membranacea (Caryophyllaceae).

Inbreeding depression and selfing rates were investigated in Schiedea membranacea (Caryophyllaceae), a hermaphroditic species endemic to the Hawaiian Islands. Most theoretical models predict high inbreeding depression in outcrossing hermaphroditic species and low inbreeding depression in inbreeding species. Although high outcrossing rates and high levels of inbreeding depression are characteristic of many species of Schiedea, self- fertilization is common among relatives of hermaphroditic S. membranacea, and high selfing rates and low levels of inbreeding depression were predicted in this species. Sixteen individuals grown in the greenhouse were used to produce selfed and outcrossed progeny. Inbreeding depression, which was evident throughout the stages measured (percentage viable seeds per capsule, mean seed mass, percentage seed germination, percentage seedling survival, and biomass after 8 mo), averaged 0.70. Inbreeding depression among maternal families varied significantly for all measured traits and ranged from -0.12 to 0.97. Using isozyme analysis, the multilocus selfing rate varied from 0.13 to 0.38 over 4 yr. Contrary to the initial prediction of high selfing and low inbreeding depression based on phylogenetic relationships within Schiedea, low selfing rates and high levels of inbreeding depression were found in S. membranacea. These results indicate that outcrossing is stable in this species and maintained by high levels of inbreeding depression.

Journal Article↗
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↗
PubMed2006

Inbreeding depression and mixed mating in Leptosiphon jepsonii: a comparison of three populations.

BACKGROUND AND AIMS: Inbreeding depression is thought to play a central role in the evolution and maintenance of cross-fertilization. Theory indicates that inbreeding depression can be purged with self-fertilization, resulting in positive feedback for the selection of selfing. Variation among populations of Leptosiphon jepsonii in the timing and rate of self-fertilization provides an opportunity to study the evolution of inbreeding depression and mating systems. In addition, the hypothesis that differences in inbreeding depression for male and female fitness can stabilize mixed mating in L. jepsonii is tested. METHODS: In a growth room experiment, inbreeding depression was measured in three populations with mean outcrossing rates ranging from 0.06 to 0.69. The performance of selfed and outcrossed progeny is compared at five life history stages. To distinguish between self-incompatibility and early inbreeding depression, aborted seeds and unfertilized ovules were counted in selfed and outcrossed fruits. In one population, pollen and ovule production was quantified to estimate inbreeding depression for male and female fitness. KEY RESULTS: Both prezygotic barriers and inbreeding depression limited self seed set in the most outcrossing population. Cumulative inbreeding depression ranged from 0.297 to 0.501, with the lowest value found in the most selfing population. Significant inbreeding depression for early life stages was found only in the more outcrossing populations. Inbreeding depression was not significant for pollen or ovule production. CONCLUSIONS: The results provide modest support for the hypothesized relationship between inbreeding depression and mating systems. The absence of early inbreeding depression in the more selfing populations is consistent with theory on purging. Differences in male and female expression of inbreeding depression do not appear to stabilize mixed mating in L. jepsonii. The current estimates of inbreeding depression for L. jepsonii differ from those of previous studies, underscoring the effects of environmental variation on its expression.

Biomass↗
PubMed1999

The genetic basis of inbreeding depression.

Data on the effects of inbreeding on fitness components are reviewed in the light of population genetic models of the possible genetic causes of inbreeding depression. Deleterious mutations probably play a major role in causing inbreeding depression. Putting together the different kinds of quantitative genetic data, it is difficult to account for the very large effects of inbreeding on fitness in Drosophila and outcrossing plants without a significant contribution from variability maintained by selection. Overdominant effects of alleles on fitness components seem not to be important in most cases. Recessive or partially recessive deleterious effects of alleles, some maintained by mutation pressure and some by balancing selection, thus seem to be the most important source of inbreeding depression. Possible experimental approaches to resolving outstanding questions are discussed.

Animals↗
PubMed2003

Maternal and fetal inbreeding depression for 70-day nonreturn and calving rate in Holsteins and Jerseys.

Inbreeding depression for 70-d nonreturn rate was estimated in 50,613 Holstein and 47,673 Jersey cows with five-generation pedigrees using an animal model. Heritabilities of 70-d nonreturn rate were very low for both breeds (1 to 2%). Maternal inbreeding depression was small (3% reduction for 10% inbreeding) and significant only for Jerseys. Fetal and maternal inbreeding depression was not significant for individual parities in Holsteins, but maternal inbreeding depression was significant in first parity only in Jerseys. Maternal and fetal inbreeding depression of calving rate (verified by a subsequent calving) was estimated on separate datasets by parity from 13,229 to 26,876 Holstein and 7374 to 11,742 Jersey cows. First-parity estimates for heritability of calving rate were 1% or less, whereas estimates for later parities varied from 1 to 6%. Significant inbreeding depression in first-parity Holsteins reduced calving rate by 4% per 10% maternal or fetal inbreeding, but effects, while undesirable, were not consistently significant in other parities. In Jerseys, maternal inbreeding significantly reduced calving rate by 6% per 10% inbreeding in first parity, and was undesirable but not significant for second through fourth parities. Fetal inbreeding depression was not significant in Jerseys. Maternal inbreeding depression of 70-d nonreturn and calving rate was small, undesirable, but not consistently significant across breeds and parities. The cumulative economic impact of maternal or fetal inbreeding on lifetime reproductive performance of Holstein or Jersey cows would be more dramatic than results for a single breeding.

Animals↗