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Selected Publication:

Type of publication: Doctoral Thesis
Type of document:

Year: 2010

Authors: Santos Nunes, MD

Title: Evolution of mitochondrial DNA in Drosophila.

Other title: Evolution der mitochondrialen DNA in Drosophila

Source: Dissertation, Vet. Med. Univ. Wien, pp. 233.


Advisor(s):

Schlötterer Christian

Reviewer(s):
Müller Mathias

Vetmed Research Units:
Institute of Population Genetics


Graduation date: 07.06.10


Abstract:
Mitochondrial DNA (mtDNA) is widely used in evolutionary studies. Its popularity as a molecular marker is due to its generally high and constant mutation rate, neutral evolution and uniparental transmission. However, several exceptions to these general rules have been reported recently in the literature. Taking advantage of advances in DNA sequencing and polymorphism detection technology, it is timely to re-evaluate if many of the assumptions still hold in the model organism Drosophila melanogaster. To assess the relative roles of selection and drift shaping the evolution of mtDNA, the pattern of mtDNA sequence variation among natural populations of D. melanogaster was compared to that obtained from a large number of neutral nuclear loci. We found that demography alone was not sufficient to explain the observed patterns of mtDNA variation. Wolbachia, a maternally inherited bacterium capable of spreading through host populations by inducing cytoplasmic incompatibility (CI), could be responsible for the observed patterns of mtDNA diversity. To test this hypothesis, we surveyed mtDNA variation and infection status in an extended dataset. Indeed, we found that the preferential infection of some mtDNA haplotypes seems be caused by a recent spread of mtDNA haplotypes associated with the infection. Furthermore we found that CI levels are insufficient to account for the spread of a Wolbachia infection in a population from Crete followed by an almost complete mtDNA replacement. These findings suggest a fitness advantage of the Wolbachia infection. In addition, the recent development of sensitive methods (e.g. such as quantitative real time PCR) allowed us to re-evaluate the assumptions of strict maternal transmission and absence of recombination in D. melanogaster. We showed that paternal leakage of mtDNA is quite common in natural populations of D. melanogaster leading to a high frequency of heteroplasmic individuals. Despite this high level of heteroplasmy, we found no evidence for recombination between mtDNA molecules. Finally, taking advantage of the recent speciation event that led to the emergence of D. simulans, D. sechellia and D. mauritiana, we studied the signatures of hybridization between two of those species, D. simulans and D. mauritiana left by the mtDNA. We found several cases of closely related mtDNA haplotypes occurring in both species and showed that the presence of these haplotypes is more likely to result from introgression of mtDNA from one species to the other than from extant ancestral polymorphism. Altogether these findings have important consequences for the use of mtDNA in Evolutionary Biology and provide further support to the growing view that mtDNA cannot be used as a single marker for population history, migration and species identification.

Keywords:
mitochondrial DNA / Drosophila / evolution / population genetics


Publication(s) resulting from University thesis:

Nunes, MD; Wengel, PO; Kreissl, M; Schlötterer, C (2010): Multiple hybridization events between Drosophila simulans and Drosophila mauritiana are supported by mtDNA introgression. Mol Ecol. 2010; 19(21):4695-4707
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Nunes, MD; Neumeier, H; Schlötterer, C (2008): Contrasting patterns of natural variation in global Drosophila melanogaster populations. Mol Ecol. 2008; 17(20):4470-4479

Nunes, MD; Nolte, V; Schlötterer, C (2008): Nonrandom Wolbachia infection status of Drosophila melanogaster strains with different mtDNA haplotypes. Mol Biol Evol. 2008; 25(11):2493-2498
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