When the 'simw[501]' mitochondrial genome, which contains the Dsim\mt:tRNA:Y^w501 allele, is introgressed into the nuclear Aats-tyr-m^Ore mutant background, the following phenotypes are observed (compared to introgression into a wild type nuclear Aats-tyr-m background): flight performance is poorer; climbing ability is not significantly affected; indirect flight muscle mitochondrial cristae are loosely packed, display large gaps, and mitochondria per unit area are increased.

When developed at 25[o]C, Dsim\mt:tRNA:Y^w501/Aats-tyr-m^Ore flies (containing mitochondrial-nuclear hybrid strains with both the D. melanogaster nuclear genome and a D. simulans mitochondrial genomes) exhibit a severely extended development time, decreased OXPHOS activity, reduced female fecundity, and shortened mechanosensory bristles. These flies exhibit a significant extension in development time by almost three days, at 28[o]C, compared to controls. The magnitude and significance of this delay decreases as the temperature increases. When larvae develop at 16[o]C, the mitochondrial-nuclear interaction does not significantly affect development time. When developed at 28[o]C, Dsim\mt:tRNA:Y^w501/Aats-tyr-m^Ore flies do not produce offspring. This heat-induced sterility is observed in both sexes and is reversible.

Relative to compatible genotypes, Dsim\mt:tRNA:Y^w501/Aats-tyr-m^Ore flies experience a 28% and 38% decrease in survival to pupation at 22[o] and 25[o]C, respectively. Those larvae that do survive to pupation do not exhibit any further effects and proceed through metamorphosis as wild-type. Survival of pupae to adult eclosion is high, even though metamorphosis time is extended at 25[o]C.

At 22[o] and 25[o]C, Dsim\mt:tRNA:Y^w501/Aats-tyr-m^Ore larvae crawl to lower heights in a climbing assay than other genotypes, suggesting a compromised energetic capacity. The mitochondrial-nuclear interaction effect is nearly significant at 16[o]c. However, at this cooler temperature the sign of the epistatic effect is reversed; Dsim\mt:tRNA:Y^w501/Aats-tyr-m^Ore larvae pupated among the highest heights of any genotype.

When developed at either 16[o] or 25[o]C, Dsim\mt:tRNA:Y^w501/Aats-tyr-m^Ore larvae are smaller than other genotypes. However, for their mass, the metabolic rate of Dsim\mt:tRNA:Y^w501/Aats-tyr-m^Ore larvae is significantly higher than that of all other genotypes when developed and measured at 25[o]C, but not when developed at 16[o]C. This result suggests that Dsim\mt:tRNA:Y^w501/Aats-tyr-m^Ore larvae metabolize energy stores at a higher rate than other genotypes when developed at warmer, but not cooler temperatures. Combined with the extended development time at 25[o]C, this indicates that energy metabolism in Dsim\mt:tRNA:Y^w501/Aats-tyr-m^Ore is less efficient, with larvae burning more energy and requiring longer development time to attain critical weight and commit to metamorphosis.

Mitochondrial-nuclear hybrid strains containing the D. melanogaster nuclear genome and a D. simulans mitochondrial genome show an incompatible mitochondrial-nuclear genotype when the nuclear genome contains Aats-tyr-m^Ore and the mitochondrial genome contains Dsim\mt:tRNA:Y^w501. Egg-to-adult development time is delayed by approximately two days via an extension of both larval development time and pupal metamorphosis, female fecundity is decreased by 50% and the adult thoracic mechanosensory bristles are shortened in these animals. Analysis of the effect of Aats-tyr-m^Ore on the phenotypes indicates that the effect on development time is largely recessive, the reduction in fecundity is a dominant effect and the effect on bristle length is nearly additive and that the negative phenotypic effects are dependent on Dsim\mt:tRNA:Y^w501 being present.