RESUMO
The influence of mitochondrial DNA (mtDNA) mutations on human disease has been extensively studied, but the impact of mutations within the adaptive range is debated. We studied males from lines of Drosophila melanogaster that have a highly standardized nuclear genome but different mtDNA, at two ages. We measured mitochondrial respiration on permeabilized muscle fibers, hydrogen peroxide production of isolated mitochondria and mtDNA copy number of whole individuals. The results show that a small set of naturally occurring mtDNA mutations can have a significant influence on mitochondrial bioenergetics that may change as the organism ages.
Assuntos
DNA Mitocondrial/genética , Drosophila melanogaster/fisiologia , Metabolismo Energético , Mitocôndrias/genética , Mitocôndrias/fisiologia , Mutação , Animais , Respiração Celular , Peróxido de Hidrogênio/metabolismo , Masculino , Fibras Musculares Esqueléticas/metabolismoRESUMO
One of the grand challenges of the postgenomics era is to mechanistically link the genotype with the phenotype. Here, we consider the link between the mitochondrial genotype and the organismal phenotype that is provided by bioenergetic studies of the electron transport chain. That linkage is pertinent for the fields of molecular ecology and phylogeography as it tests if, and potentially how, natural selection can influence the evolutionary and demographic past of both populations and species. We introduce the mitochondrial genotype in terms of mitochondrial-encoded genes, nuclear-encoded genes that produce structural proteins imported into the mitochondria, and mitochondrial DNA-nuclear interactions. We then review the potential for quaternary structure modelling to predict the functional consequence of specific naturally occurring mutations. We discuss how the energy-producing reactions of oxidative phosphorylation can be used to provide a mechanistic biochemical link between genotype and phenotype. Experimental manipulations can then be used to test the functional consequences of specific mutations in multiple genetic backgrounds. Finally, we examine how mitochondria can influence the organismal mitochondrial phenotype using the examples of lifespan, fertility and starvation resistance and discuss how mitochondria may be involved in establishing both the upper and lower thermal limits of organisms. We conclude that mitochondrial DNA mutations can be important in determining aspects of organism life history. The question that remains to be resolved is how common are these adaptive mutations?
Assuntos
Evolução Molecular , Genótipo , Mitocôndrias/genética , Fenótipo , Adaptação Biológica/genética , Núcleo Celular/genética , DNA Mitocondrial/genética , Metabolismo Energético , Genes Mitocondriais , Variação Genética , Modelos Moleculares , Mutação , Fosforilação Oxidativa , Estrutura Quaternária de ProteínaRESUMO
Stress resistance traits in Drosophila often show clinal variation, suggesting that selection affects resistance traits either directly or indirectly. One of the most common causes of stress for animals is the shortage or suboptimal quality of food, and individuals within many species must survive periods of starvation or exposure to nutritionally imbalanced diets. This study determines the relationship between starvation resistance, body lipid content, and lifespan in five recently collected Drosophila simulans populations from four distinct geographic localities. Despite rearing under standard nutritional conditions, we observed significant differences in starvation resistance between sexes and between localities. If body lipid proportion is included as a covariate in statistical analysis the difference between the sexes remains (slopes are parallel, with males more susceptible than females to starvation across all lipid proportions) but the effect of locality disappears. This result suggests that flies from different localities differ in their susceptibility to starvation because of differences in their propensity to store body lipid. We observed a negative relationship between lifespan and starvation resistance in both males and females, suggesting a fitness cost to increasing lipid reserves. These data raise issues about the role of diet in maintaining life history trait variation within and among populations. In conclusion, we show many similarities and surprising differences in life history traits between D. simulans and Drosophila melanogaster.
Assuntos
Drosophila/metabolismo , Metabolismo dos Lipídeos , Longevidade , Animais , Feminino , Geografia , Masculino , InaniçãoRESUMO
Tetracycline is commonly used to clear Wolbachia from infected insects. Studies then compare specific biochemical and/or life-history traits between infected and uninfected individuals with the same genetic background. We investigated the potential for tetracycline to influence mitochondrial efficiency and mitochondrial (mt)DNA density two generations after treatment in Drosophila simulans. We observed that antibiotic treatment resulted in a decline in inorganic phosphate incorporated into ATP per mole of oxygen consumed (ADP:O ratio). Further, tetracycline treatment caused a significant increase in mtDNA density in naturally Wolbachia-uninfected but not in naturally Wolbachia-infected lines suggesting a dosage effect. These data suggest that the current practice of comparing Wolbachia-infected and Wolbachia-uninfected insects two generations after tetracycline treatment needs to be re-evaluated.
