Morphology of the pupal heart, adult heart, and associated tissues in the fruit fly, Drosophila melanogaster

The early pupal heart of the fruit fly Drosophila melanogaster has recently been the subject of intense physiological and molecular work, yet it has n ot been well described, nor has it been compared with the heart of the adul t fly. In the work reported here, the hearts of adults and early pupae of D . melanogaster were studied by scanning and transmission electron microscop y and by Light microscopy. The hearts of adults and early pupae both consis t of a tube of circular striated muscle one cell in thickness. The alary mu scles, which suspend the heart, are more delicate in the adult compared to the early pupa. The pericardial cells in both early pupae and adults are co nnected to the heart by connective tissue radiating from the alary muscles or dorsal diaphragm. We confirm that four major changes occur in the heart during metamorphosis: 1) a conical chamber is formed de novo in the first a nd second abdominal segments; 2) the adult heart curves to conform to the c ontour of the abdomen; 3) a layer of longitudinal striated muscle appears o n the ventral surface of the heart; 4) a fourth pair of ostia is added to t he three already present in the early pupa; and note additionally that 5) t he ostia appear as simple openings in the heart of the early pupa but are v alve-like in the adult. (C) 1999 Wiley-Liss, Inc.