CLS^c01874 mutants exhibit a virtually complete loss of cardiolipin and a compensatory increase of phosphatidylglycerol. The respiratory activity of isolated CLS^c01874 mitochondria is diminished in comparison to wild-type mitochondria and the loss of cardiolipin has profound effects on fly physiology at all developmental stages, such as reduced locomotor activity at the adult stage. The lack of cardiolipin causes mitochondrial dysfunction, which leads to cardiac insufficiency, motor weakness, and early death. This physiological decline accompanied by alterations in mitochondrial ultrastructure and by re-organization of ATP synthase complexes. Many mitochondria in flight and heart muscle show abnormal morphology and this is also observed in isolated mitochondria. Aggregation of inner membranes is the most common structural abnormality. CLS^c01874 mitochondria with normal morphology are present as well.