The Effects of a Bottleneck on Inbreeding Depression and the Genetic Load

  title={The Effects of a Bottleneck on Inbreeding Depression and the Genetic Load},
  author={Mark Kirkpatrick and Philippe Jarne},
  journal={The American Naturalist},
  pages={154 - 167}
We study the effects of a population bottleneck on the inbreeding depression and genetic load caused by deleterious mutations in an outcrossing population. The calculations assume that loci have multiplicative fitness effects and that linkage disequilibrium is negligible. Inbreeding depression decreases immediately after a sudden reduction of population size, but the drop is at most only several percentage points, even for severe bottlenecks. Highly recessive mutations experience a purging… 
Inbreeding rate modifies the dynamics of genetic load in small populations
It is suggested that highly deleterious alleles can be purged in small populations already at low levels of inbreeding, but that purging does not protect the small populations from eventual genetic deterioration and extinction.
Selection, load and inbreeding depression in a large metapopulation.
The subdivision of a species into local populations causes its response to selection to change, even if selection is uniform across space. Population structure increases the frequency of homozygotes
Purging of inbreeding depression and fitness decline in bottlenecked populations of Drosophila melanogaster
The results suggest that the nature of genetic variation in fitness may greatly influence the way in which populations respond to bottlenecks and that stochastic processes play an important role.
An explicit model for the inbreeding load in the evolutionary analysis of selfing
It is found that the evolution of selfing is favored by a large recessivity of deleterious effects, while the magnitude of homozygous deleteriously effects only becomes relevant in relatively small populations.
Dominance of Deleterious Alleles Controls the Response to a Population Bottleneck
Taken together, theoretical predictions and empirical observations show that complex demographic history may facilitate rather than impede inference of parameters of natural selection.
Inbreeding depression and drift load in small populations at demographic disequilibrium
The theoretical results demonstrate that inbreeding depression and heterosis levels can vary widely across populations at disequilibrium despite similar He and highlight that joint demographic and genetic dynamics are key to predicting patterns of genetic load in nonequilibrium systems.
On the expected relationship between inbreeding, fitness, and extinction
The assumption of frequent, slightly deleterious mutations do agree with observations and experiments, on the contrary to the assumption of few, moderately deleteriously mutations, and it is clear that to infer the costs of inbreeding, one must know both the history of in breeding and population demography.
Redistribution of Gene Frequency and Changes of Genetic Variation Following a Bottleneck in Population Size
With typical estimates of mutation parameters, the joint-effect model can explain data from laboratory experiments on the effect of bottlenecking on fitness and morphological traits, providing further support for it as a plausible mechanism for maintenance of quantitative genetic variation.
Bottlenecks in large populations: the effect of immigration on population viability
A first simple genetic model uncovers the opposite effects of immigration on fitness according to the type of deleterious mutations considered, which tends to increase the probability of extinction if occurring preferentially when population density is high, while it decreases extinction if occurs preferently towards low-density populations.
Genetic load may increase or decrease with selfing depending upon the recombination environment
The results show that selection can be more or less effective in selfers as compared to outcrossers depending on the relationship between the deleterious mutation rate and gene density, and therefore different genomic regions in different taxa could show differing results.


Inbreeding depression due to mildly deleterious mutations in finite populations: size does matter.
Numerical results show that the transition between the small and the large population regimes is quite rapid, and occurs largely over a range of population sizes that vary by a factor of 10.
The effect of linkage and population size on inbreeding depression due to mutational load.
It appears that associations between neutral and selected loci may produce effects that differ according to the initial frequencies of the neutral alleles, whereas previous studies have been confined to outbreeding populations, and to alleles at frequencies close to one-half.
Purging inbreeding depression and the probability of extinction: full-sib mating
The effectiveness of purging the genetic load is examined by documenting both the reduction in inbreeding depression and the increase of the probability of extinction when there is continous full-sib mating.
In a population of constant size the expected heterozygosity for a neutral locus when mutation and genetic drift are balanced is given by 4 Nv/(4Nv + 1) under the assumption that new mutations are
Bottleneck effect on genetic variance. A theoretical investigation of the role of dominance.
The phenomenon that the genetic variance of fitness components increase following a bottleneck or inbreeding is supported by a growing number of experiments and is explained theoretically by either
Population bottlenecks and nonequilibrium models in population genetics. II. Number of alleles in a small population that was formed by a recent bottleneck.
It is suggested that populations that have undergone a single bottleneck event, followed by rapid population growth, should have an apparent excess number of alleles, given the observed level of genic heterozygosity and provided that the bottleneck has not occurred very recently.
Genetics underlying inbreeding depression in Mimulus with contrasting mating systems
It is shown here that deleterious recessive alleles are mainly responsible for inbreeding depression in two closely related annual plants, the primarily selfing Mimulus micranthus and the mixed-mating M. guttatus.
Mutation Accumulation and the Extinction of Small Populations
Application of empirical estimates of the properties of spontaneous deleterious mutations leads to the conclusion that populations with effective sizes smaller than 100 are highly vulnerable to extinction via a mutational meltdown on timescales of approximately 100 generations.
Selection against inbred song sparrows during a natural population bottleneck
It is reported that song sparrows that survived a severe population bottleneck were a non-random subset of the pre-crash population with respect to inbreeding, and that natural selection favoured outbred individuals, suggesting that inbreeding depression was expressed in the face of an environmental challenge.
  • R. Lande
  • Biology
    Evolution; international journal of organic evolution
  • 1994
Data on the rate and magnitude of mildly deleterious mutations in Drosophila melanogaster indicate that even moderately large populations, with effective sizes on the order of Ne = 103, may incur a substantial risk of extinction from the fixation of new mutations.