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Muller's ratchet in symbiont populations
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolution, Genomics and Systematics, Molecular Evolution.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Evolution, Genomics and Systematics, Molecular Evolution.
2007 (English)In: Genetica, ISSN 0016-6707, E-ISSN 1573-6857, Vol. 130, no 2, 199-211 p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
2007. Vol. 130, no 2, 199-211 p.
Keyword [en]
Nested population dynamics, Mutation accumulation, Genome degradation, Buchnera, Stochastic modelling
National Category
Biological Sciences
URN: urn:nbn:se:uu:diva-96070DOI: 10.1007/s10709-006-9007-7ISI: 000246150000010PubMedID: 16924405OAI: oai:DiVA.org:uu-96070DiVA: diva2:170528
Available from: 2007-09-04 Created: 2007-09-04 Last updated: 2011-02-02Bibliographically approved
In thesis
1. Modeling Genome Evolution: Creation, Change and Destruction
Open this publication in new window or tab >>Modeling Genome Evolution: Creation, Change and Destruction
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Historically, evolution has been studied either by looking at morphological traits in living organisms and the fossil record, or by using bioinformatics and comparative genomics. While highly useful for deducing evolutionary history, these approaches are not particularly well suited for studying the mechanisms of evolution. In order to address such issues, other methods are needed. Mathematical modelling is one of the most powerful options available, and it is the approach used in this thesis. By constructing models of biological systems, the work aims to resolve some of the many unresolved questions regarding evolutionary processes, such as how new genes evolve and how selection acts in fragmented populations. Some answers have been reached, and thus the thesis makes a small contribution to our overall understanding of evolution.

The creation of novel genes was studied both directly and by extension of an analogous system, which revolved around reversion of a frameshift mutant. The results pointed to gene amplification as a likely mechanism for both reversion of the frameshift mutant and creation of new genes.

Selection in fragmented populations is shown to be effective even when sub-populations, rather than individuals, are competing against each other. Modeling of a system of bacterial symbionts living in aphids indicates that, although the bacterial population within a single host is small and subject to rampant genetic drift, the bacterial population as a whole is regulated by selection on the host level. Thus, deleterious mutations do no accumulate and the population maintains its fitness over time.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2007. 37 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 324
Molecular biology, Theotretical biology, Population genetics, Stochastic modeling, Genome evolution, Molekylärbiologi
urn:nbn:se:uu:diva-8163 (URN)978-91-554-6941-2 (ISBN)
Public defence
2007-09-25, Zootissalen, Evolutionsbiologistcentrum, Norbyvägen 18, Uppsala, 10:00
Available from: 2007-09-04 Created: 2007-09-04Bibliographically approved

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