Evolution and physiological consequences of de-alation in crickets

Wing shedding or de-alation is a common phenomenon among crickets. Its significance and effects on other traits were examined based on the results from experiments using artifical or natural de-alation. Artificial de-alation at adult emergence induces rapid egg production and flight muscle histolysis in several species examined. However, natural de-alation does not always shorten the pre-ovipositional period because it does not occur immediately after adult emergence and because oviposition starts before de-alation. In some cases, naturally de-alated females produce more eggs than to intact females during early adult life, but peak ovipositing activity occurs before de-alation. Therefore, retention of the hindwings does not suppress high ovipositing activity in such cases. It appears that de-alation is a result rather than a causal factor in ending migration. Ovarian development and flight muscle histolysis, which can be stimulated by de-alation, are controlled by the jevenile hormone, but the mechanism inducing de-alation remains unknown. The possible factors leading to the evolution of de-alation are discussed.     

The physiological costs of flight capability in wing-dimorphic crickets

Nutritional indices, triglyceride levels and flight muscle developmental profiles were compared between long-winged (LW) and short-winged (SW; flightless) morphs of the cricketsGryllus rubens Scudder andG. firmus Scudder. This was done to identify potential physiological costs of flight capability in adults. The LW morph of each species converted a lower proportion of assimilated nutrients into biomass (reduced ECD) than did the SW morph. This documents increased respiratory metabolism in the LW morph. Triglyceride concentration was higher in LW vs. SW adults. This suggests that the elevated respiration in the LW morph may be at least partially due to the increased biosynthesis of this high energy substance. Preliminary data indicate higher respiration rates of LW functional vs. SW vestigial flight muscles. Collectively, these data suggest that the energetic cost of flight capability in adults results from biosynthesis of triglyceride flight fuel and flight muscle maintenance but not flight muscle growth. No flight muscle growth was observed in adults.     

Variability in wing form of crickets

Loss of functional hindwings is observed in most subfamilies of Japanese crickets. Habitat, behaviour, body size and phylogenetic factors might be involved, but interactions among them may obscure the general trend. Wing dimorphism is common among the relatively small-sized members of Gryllinae, and the two small-sized subfamilies, Nemobiinae and Trigonidiinae. Both environmental cues (e. g. photoperiod) and genetic factors affect the wing form. InDianemobius fascipes (Nemobiinae), the percentage macroptery was drastically changed by selection for macroptery or microptery. Crossing experiments indicated polygenic control of wing form as well asX-chromosomal and maternal effects. Neither the long-winged nor short-winged line bred true after 40 generations of selection. Full-sib families revealed a large genetic variation in frequency of macropterous forms within a population. The genetic determination of the propensity for macropterism did not seem to be directly coupled to the mechanism performing the photoperiodic time-measurement.