BENDLESS ALTERS THORACIC MUSCULATURE IN DROSOPHILA

bendless- (ben-) is an X chromosome mutation in Drosophila melanogaste r, known to alter patterns of connections in the CNS and thus modify b ehavior (Thomas and Wyman, 1984). We report that in addition to its CN S effects, ben- has. pleiotropic phenotypes affecting thoracic muscle patterning, pupal mortality, and post-eclosional mobility. The tergal depressor of the trochanter (TDT) normally attaches ventrally to an ap odeme on the trochanter and dorsally to the lateral scutum just poster ior to the intrascutal suture, In ben- individuals, TDT may attach any where within the boundaries of the attachment areas for TDT and dorsov entral muscles I (DVM I) and II (DVM II). Furthermore, TDT may complet ely lack a dorsal attachment, although it still maintains a ventral at tachment. DVMs may also attach abnormally to dorsal sites normally occ upied by an adjacent DVM, or may be entirely eliminated. DVM loss occu rs independently of the position or presence of TDT dorsal attachment. The cytology of ben- TDT is altered. Muscles may have fibers that are swollen and stain abnormally. Other fibers may have large, axially al igned holes. ben- flies have an increased likelihood of failing to ecl ose and, upon eclosion, show impaired mobility. We describe several po ssible mechanisms for the ben- developmental defects and discuss this mutation in light of its evolutionary significance.