Muller's ratchet in symbiont populations

Muller's ratchet, the inevitable accumulation of deleterious mutations in asexual populations, has been proposed as a major factor in genome degradation of obligate symbiont organisms. Essentially, if left unchecked the ratchet will with certainty cause extinction due to the ever increasing mut...

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Bibliographic Details
Published in:Genetica 2007-06, Vol.130 (2), p.199-211, Article 199
Main Authors: Pettersson, Mats E, Berg, Otto G
Format: Article
Language:English
Subjects:
Accumulation
Animal reproduction
Animals
Aphids - microbiology
Biologi
Biology
Buchnera
Buchnera - genetics
Buchnera - growth & development
Degradation
Extinction
Genome degradation
Genome, Bacterial
Genomes
Insects
Mathematical models
Models, Genetic
Mutation
Mutation accumulation
NATURAL SCIENCES
NATURVETENSKAP
Nested population dynamics
Population structure
Populations
Selection, Genetic
Stochastic modelling
Stochastic Processes
Structural hierarchy
Subpopulations
Symbionts
Symbiosis - genetics
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Summary:Muller's ratchet, the inevitable accumulation of deleterious mutations in asexual populations, has been proposed as a major factor in genome degradation of obligate symbiont organisms. Essentially, if left unchecked the ratchet will with certainty cause extinction due to the ever increasing mutational load. This paper examines the evolutionary fate of insect symbionts, using mathematical modelling to simulate the accumulation of deleterious mutations. We investigate the effects of a hierarchical two level population structure. Since each host contains its own subpopulation of symbionts, there will be a large number of small symbiont populations linked indirectly via selection on the host level. We show that although the separate subpopulations will accumulate deleterious mutations quickly, the symbiont population as a whole will be protected from extinction by selection acting on the hosts. As a consequence, the extent of genome degradation observed in present day symbionts is more likely to represent loss of functions that were (near-) neutral to the host, rather than a snap shot of a decline towards complete genetic collapse.
ISSN:0016-6707
1573-6857
1573-6857
DOI:10.1007/s10709-006-9007-7