Mutational meltdown
Encyclopedia
Mutational meltdown refers to the process by which a small population
accumulates harmful mutation
s, which leads to loss of fitness
and decline of the population size, which may lead to further accumulation of deleterious mutations due to inbreeding depression
. A population experiencing mutational meltdown is trapped in a downward spiral and will go extinct if the phenomenon lasts for some time. Usually, the deleterious mutations would simply be selected
away, but during mutational meltdown, the number of individuals thus suffering an early death is too large relative to overall population size so that mortality exceeds the birth rate
.
The accumulation of mutations in small populations can be divided into three phases. In the second phase a population starts in mutation/selection equilibrium, mutations are fixed at a constant rate through time, and the population size is constant because the fecundity exceeds mortality. However, after a sufficient number of mutations have been fixed in the population, the birth rate is slightly less than the death rate, and the population size begins to decrease. The smaller population size allows for a more rapid fixation of deleterious mutations, and a more rapid decline of population size, etc.
Small population size
Small populations behave differently from larger populations. They often result in population bottlenecks, which have harmful consequences for the survival of that population.-Demographic effects:...
accumulates harmful mutation
Mutation
In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...
s, which leads to loss of fitness
Fitness (biology)
Fitness is a central idea in evolutionary theory. It can be defined either with respect to a genotype or to a phenotype in a given environment...
and decline of the population size, which may lead to further accumulation of deleterious mutations due to inbreeding depression
Inbreeding depression
Inbreeding depression is the reduced fitness in a given population as a result of breeding of related individuals. It is often the result of a population bottleneck...
. A population experiencing mutational meltdown is trapped in a downward spiral and will go extinct if the phenomenon lasts for some time. Usually, the deleterious mutations would simply be selected
Selection
In the context of evolution, certain traits or alleles of genes segregating within a population may be subject to selection. Under selection, individuals with advantageous or "adaptive" traits tend to be more successful than their peers reproductively—meaning they contribute more offspring to the...
away, but during mutational meltdown, the number of individuals thus suffering an early death is too large relative to overall population size so that mortality exceeds the birth rate
Birth rate
Crude birth rate is the nativity or childbirths per 1,000 people per year . Another word used interchangeably with "birth rate" is "natality". When the crude birth rate is subtracted from the crude death rate, it reveals the rate of natural increase...
.
The accumulation of mutations in small populations can be divided into three phases. In the second phase a population starts in mutation/selection equilibrium, mutations are fixed at a constant rate through time, and the population size is constant because the fecundity exceeds mortality. However, after a sufficient number of mutations have been fixed in the population, the birth rate is slightly less than the death rate, and the population size begins to decrease. The smaller population size allows for a more rapid fixation of deleterious mutations, and a more rapid decline of population size, etc.
See also
- Muller's ratchetMuller's ratchetIn evolutionary genetics, Muller's ratchet is the process by which the genomes of an asexual population accumulate deleterious mutations in an irreversible manner....
- Small population sizeSmall population sizeSmall populations behave differently from larger populations. They often result in population bottlenecks, which have harmful consequences for the survival of that population.-Demographic effects:...
- Extinction VortexExtinction VortexExtinction vortices are a class of models through which conservation biologists, geneticists and ecologists can understand the dynamics of and categorize extinctions in the context of their causes. Developed by M. E. Gilpin and M. E...
Further reading
- W. Gabriel, M. Lynch, and R. Burger (1993). Muller's Ratchet and mutational meltdowns. Evolution 47:1744-1757.
- M. Lynch, R. Burger, D. Butcher, and W. Gabriel (1993). The mutational meltdown in asexual populations. J. Hered. 84:339-344.
- M. Lynch and W. Gabriel (1990). Mutation load and the survival of small populations. Evolution 44:1725-1737.
- M. Lynch, J. Conery, and R. Burger (1995) Mutational meltdowns in sexual populations. Evolution 49:1067-1080.