GENDER-SPECIFIC DEVELOPMENTAL TRANSFORMATION OF A COCKROACH BIFUNCTIONAL MUSCLE

Adult male and female cockroaches, Periplaneta americana, differ in th eir capacity for sustained flight. Tethered 20 day adult males flap th eir wings about 15 min; females 12 seconds. Males are less massive and have greater total wing area than do females, with wing loading only about half that of the female. The basalar muscle, a major wing depres sor in flight, is also sexually dimorphic. In males it is 1.5x more ma ssive and has a cross sectional area 1.2x greater than the female homo logue. Muscle fibers of the adult male and female basalar muscles are ultrastructurally and biochemically distinct. Female fibers have a myo filament array similar to that of other non-flight locomotory muscles, with 10-12 actin filaments surrounding each myosin filament. Adult ma le fibers typically have six actin filaments around each myosin filame nt. The male fibers also appear to be more oxidative. The volume densi ty of mitochondria is about 3x greater and the specific activity for c itrate synthase, an oxidative indicator, is 3.5x greater in male fiber s than in female fibers. Male basalar muscle shows an enhanced ability to resist fatigue when its motoneurone is stimulated at flight freque ncy; homologues from the male terminal nymph and 20 day adult female a re both highly fatiguable. The basalar muscle of both male and female terminal nymphs are similar in ultrastructural and biochemical profile and are not greatly different from the adult female. In male roaches there may be important neuronal or hormonal inputs at about the time o f the terminal molt to adulthood that direct the transformation of the basalar muscle in time for the assumption of a new behavioral role-fl ight. (C) 1994 Wiley-Liss, Inc.