Abstract
Drosophila obscura is a very common fruit fly inhabiting European forests. This species has a large number of mitochondrial haplotypes of Cyt b gene. We used experimental lines of D. obscura to test the adaptive significance of intra-population variability of the mitochondrial genome (mtDNA) and selective forces that maintain it. We chose three isofemale lines with distinct mitochondrial haplotypes of Cyt b gene from each of the two populations sampled in Serbia. Using backcrossing, we created nine experimental lines for each population with all combinations of mtDNA haplotypes and nuclear genetic backgrounds (nuDNA). Individuals of both sexes were tested separately for desiccation resistance at two temperatures. Cox proportional hazards model, with four factors: mtDNA, nuDNA, sex and temperature was used to analyze the survival data. In some comparisons we noticed significant effect of mtDNA on desiccation resistance, while all of them showed significant effect of interaction between mitochondrial and nuclear genome. Temperature in interaction with mtDNA or mito-nuclear genotype more frequently showed significant effect on desiccation resistance compared to sex in interaction with mtDNA or mito-nuclear genotype. Our result show adaptive significance of intra-population variation of mtDNA and importance of interactions between mitochondrial and nuclear genome on fitness. Temperature specific mito-nuclear interaction rather than sex-specific selection on mito-nuclear genotypes maintains mtDNA variability in this model species.
Highlights
Variation in the mtDNA has long been considered selectively neutral [1,2]
We noticed a significant effect of mtDNA genotype on desiccation resistance in two out of three pairwise comparisons, not being significant in comparison II vs III which differ by six mutations all synonymous
Our results have several important findings. They show that mtDNA variants have a significant effect on fitness, which was measured by desiccation resistance
Summary
Variation in the mtDNA has long been considered selectively neutral [1,2] This view was based solely on the properties of the mitochondrial genome (mtDNA), it is haploid, there is no dominance and its inheritance is mostly uniparental. Interactions between the two genomes are complex and encompass several important biological processes such as cellular respiration, mtDNA replication, transcription, and translation. All of these processes require sequences coded from both genomes [5,6,7,8]
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