Fitness ofDrosophila melanogaster(Diptera: Drosophilidae) Following Bacterial Infection Under Influence of Two Different Diet Regimes and Host Heterogeneity

Following bacterial infection spreads in a population, individuals show fitness variation or plasticity based on their genotypes, the environmental stress and the interaction of both factors. Drosophila melanogaster-bacterial pathogen system was used to unravel how fitnessdivergent isofemale (homogeneous) lines and experimental population (heterogeneous) react to infection under standard and restricted diets. Life-history traits and fecundity of D. melanogaster were assessed under healthy and disease conditions. Marked differences were observed between half of the Drosophila lines and the heterogeneous population. Diet change failed to induce significant differences of survival percentage and development time in all lines, indicating lack of phenotypic plasticity under healthy conditions. However, following bacterial infection, the significant differences among the Drosophila life-history traits due to lines and bacterial strains demonstrated phenotypic plasticity and genotypeby- environment interaction on standard diet. By combining the two environmental factors (diet regime and treatment) together with the lines, D. melanogaster showed significant difference of the survival percentage due to Pectobacterium carotovorum infection. Interestingly, Drosophila fecundity was affected by genotype, diet and treatment. The fecundity showed a general reduction following infection or diet restriction exposure. The results of reaction norms of Drosophila survival percentage, development time and fecundity demonstrated that the isofemale lines were more plastic than the heterogeneous population under the range of environments tested. The obtained results give evidence that the fitness plasticity is considered an important mechanism to help the homogeneous populations to survive the harsh environmental circumstances, whereas the phenotypic variation of the heterogeneous populations is considered the major one.