Continuous Variation in Wing Length and Flight Musculature in a Tropical Field Cricket, Teleogryllus derelictus : Implications for the Evolution of Wing Dimorphism

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Wing polymorphism with continuous variation in flight musculature was discovered in a tropical field cricket, Teleogryllus derelictus Gorochov derived from Java, Indonesia. In this species, typical short-winged (SW) and long-winged (LW) morphs often observed in other species of cricket were found, but individuals with intermediate wing lengths (IM morph) were also observed. However, the frequency distribution in relative wing lengths, i.e. hind wing length (HW)/fore wing length (FW), was bimodal with a relatively low frequency of IM morphs. Flight muscle mass at adult emergence was directly related to HW/FW and the variation was continous. It changed little after adult emergence in SW morphs, but showed a>70% increase in some LW morphs whereas a reduction in mass due to histolysis occurred in IM and other LW individuals. Flight muscle growth and histolysis were accompanied by conspicuous color changes apparently related to cytochrome c. The total fat and triacylglycerol contents of the body were closely related to body weight, but not to HW/FW. Some LW adults flew out of the rearing tanks within a week after adult emergence. In response to a synthetic adipokinetic hormone (AKH), both LW and SW adults were capable of forming low-density lipophorin (LDLp), which is known to be important in mobilizing lipid fuel for flight activity in other insects. The methanol extracts of corpora cardiaca taken from both LW and SW morphs showed AKH activity, indicating that inter-morph physiological differentiation has not occurred in the lipid-mobilization system. The present results with T. derelictus do not support Roff's hypothesis that a reduction in flight muscles occurred before that in wing length during the course of evolution for wing dimorphism, but may suggest an alternative evolutionary pathway.


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