A quantitative ultrastructural study of flight muscle in Musca domestica with experimentally lengthened lifespans

Abstract

Houseflies bred from egg through larval and pupal stages at 25°C were reared at 18°C after emergence to experimentally extend their maximum lifespan. The fine structure of flight muscles from these houseflies at 68 days (0–18° flies) was compared to that of houseflies of the same age but reared at 25°C throughout (0–25° flies) and to that of 37-day-old adult flies. Myofibrillar structure was preserved in all three sets of flies. Morphometric study revealed that the total fiber volume and fractional values of a number of parameters were similar in the three sets of flies. The fractional mitochondrial volume in 0–18° and 0–25° flies were similar (31%), less than the value for the adult flies (34%). The striking finding was that the volume of the mitochondrial cristal array decreased only by 24% in the 0–18° flies, compared to the 55% decrease seen in the 0–25° flies. The greater preservation of cristal array in the muscle of 0–18° flies strengthens the idea that the cristae are important to senescene in the organism and suggests a mechanism by which lowered ambient temperature may prolong lifespan in this poikilotherm.