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Mutational meltdown in laboratory yeast populations.
C Zeyl1, M Mizesko, J A de Visser
1Department of Biology, Wake Forest University, Winston-Salem, North Carolina 27109, USA. zeylcw@wfu.edu
Evolution; International Journal of Organic Evolution
|June 30, 2001
Summary
High mutation rates increase extinction risk in small populations, as predicted by mutational meltdown theory. This study experimentally demonstrates how increased mutation accumulation drives population decline and extinction in Saccharomyces cerevisiae.
Area of Science:
- Evolutionary Biology
- Population Genetics
- Microbial Ecology
Background:
- Mutations can accumulate in small populations due to genetic drift, potentially leading to fitness declines.
- Mutational meltdown models predict that these fitness declines can accelerate mutation accumulation, leading to population collapse and extinction.
- The mutation rate is a key factor influencing the risk and speed of mutational meltdown.
Purpose of the Study:
- To experimentally test the predictions of mutational meltdown models.
- To investigate the relationship between mutation rate and extinction risk in controlled populations.
- To assess the impact of genetic drift and mutation accumulation on population fitness and size.
Main Methods:
- Established 12 replicate populations of Saccharomyces cerevisiae from two isogenic strains with mutation rates differing by two orders of magnitude.
- Maintained populations at a fixed effective population size (near 250) through daily transfers for approximately 2900 generations (175 transfers).
- Monitored population size, fitness (growth rate), and extinction events to identify patterns related to mutation rate.
Main Results:
- Two extinctions occurred, exclusively in populations with elevated mutation rates.
- Direct evidence confirmed mutational meltdown as the cause of extinction in one population, evidenced by a major fitness decline and recurrence in re-established populations.
- Populations with wild-type mutation rates showed no size decrease and generally increased in fitness over time.
Conclusions:
- Experimental results support the mutational meltdown theory, demonstrating that higher mutation rates increase extinction probability in small, genetically drifting populations.
- The study highlights the critical role of mutation rate in determining the long-term viability of populations facing genetic drift.
- Saccharomyces cerevisiae populations with significantly elevated mutation rates are susceptible to extinction via mutational meltdown, while wild-type populations can adapt and increase fitness.