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Nonrandom partition of mitochondria in heteroplasmic Drosophila
1Laboratoire de Zoogéographie, Université Paul Valéry, Montpellier, France. stordeur@bred.univ-montp3.fr
Abstract:
In order to understand the status of heteroplasmy and its evolution within the Drosophila melanogaster subgroup, cytoplasm microinjections between eggs were performed involving three lineages of Drosophila simulans, carrying the siI, siII or siIII mtDNA type, respectively, and two strains of Drosophila mauritiana carrying the maI or maII mtDNA type. Progeny of eggs from all combinations of injection were analysed. The maII or siI molecules, when provided by the donor, were never detected in the offspring of the hosts, whatever the host's mitochondrial type. Heteroplasmic flies were detected when siII, siIII or maI mitochondria were injected into any of the other cytoplasms. In the majority of cases the percentage of foreign mtDNA increased over generations, leading to a complete replacement of the endogenous mtDNA. In most cases, siII was prevalent. The stochastic processes involved in the evolution of heteroplasmic states are strongly affected by selective values of the different mtDNA types, with a clear hierarchy among them: siII has the most advantage, then siIII and maI, and finally siI and maII. In the siII/maII heteroplasmy case, the loss of maII was more rapid at a high temperature.
Insights
Mitochondrial DNA (mtDNA) competition in Drosophila shows that some types, like siII, are favored and can replace others over generations. Temperature also influences the rate of mtDNA replacement in heteroplasmic flies.
Area of Science:
- Evolutionary Biology
- Genetics
- Molecular Biology
Background:
- Mitochondrial DNA (mtDNA) heteroplasmy, the coexistence of different mtDNA types within an organism, is crucial for understanding evolutionary dynamics.
- The Drosophila melanogaster subgroup provides a model system to study the selective pressures and evolutionary trajectories of mtDNA variants.
Purpose of the Study:
- To investigate the evolutionary fate of different mitochondrial DNA (mtDNA) types during cytoplasmic microinjections in Drosophila.
- To determine the selective hierarchy and potential for replacement among distinct mtDNA haplotypes within the Drosophila melanogaster subgroup.
Main Methods:
- Cytoplasmic microinjections were performed between eggs of Drosophila simulans (siI, siII, siIII mtDNA types) and Drosophila mauritiana (maI, maII mtDNA types).
- Offspring from all injection combinations were analyzed to track the presence and proportion of donor and host mtDNA over generations.
Main Results:
- Specific mtDNA types (maII, siI) were never detected in offspring, indicating strong selective incompatibility.
- Heteroplasmy was established with siII, siIII, or maI mtDNA, often leading to the replacement of endogenous mtDNA over generations, with siII frequently being prevalent.
- A clear selective hierarchy was observed: siII > siIII ≈ maI > siI ≈ maII, influencing the outcome of heteroplasmy.
- High temperatures accelerated the loss of maII mtDNA in siII/maII heteroplasmy.
Conclusions:
- The evolution of heteroplasmy is significantly influenced by the selective values of different mtDNA types, leading to predictable replacement patterns.
- Drosophila mtDNA types exhibit varying degrees of competitive advantage, shaping their evolutionary trajectories within populations.
- Environmental factors, such as temperature, can modulate the rate of mtDNA replacement in heteroplasmic individuals.