FLIGHT-MUSCLE POLYMORPHISM IN THE CRICKET GRYLLUS-FIRMUS - MUSCLE CHARACTERISTICS AND THEIR INFLUENCE ON THE EVOLUTION OF FLIGHTLESSNESS

Flight muscles of the cricket Gryllus firmus are polymorphic, existing as pink or white phenotypes. White muscles are smaller in size, have reduced number and size of muscle fibers, and have reduced in vitro en zyme activities and respiration rates relative to pink muscles of newl y molted, fully winged adults. G. firmus is also polymorphic for wing length. All newly molted long-winged adults exhibited the pink-muscle phenotype, while most newly molted short-winged adults exhibited the w hite-muscle phenotype, which resulted from arrested muscle growth. As long-winged adults aged, fully grown pink muscle was transformed into white muscle via histolysis. The substantially higher respiration rate of pink muscle likely contributes to the elevated whole-organism resp iration rate of long-winged females, which has been documented previou sly and which is thought to divert nutrients from egg production. Hist olyzed white flight muscle from long-winged crickets also exhibited si gnificantly elevated respiration rate and enzyme activities compared w ith underdeveloped white muscle from short-winged adults, although the se differences were not as great as those between pink and white muscl es. Fecundity was much more elevated in females with white versus pink flight muscles than it was in females with short versus long wings. T he fitness gain resulting from flightlessness has typically been estim ated in previous studies by comparing enhanced egg production of short -winged and long-winged females, without considering the influence of flight-muscle variation. Our results suggest that the magnitude of thi s fitness gain has been substantially underestimated.