Abstract
Although there is a considerable amount of information on the ecology, genetics and physiology of life-history traits there is little information on the morphological variations associated with flight ability within species. In this paper, the morphology and ultrastructure of certain organelles in the flight muscles of Gryllus firmus are recorded using transmission electron microscopy. The ultrastructure of the flight muscles of 7-day-old female adults reveals that the ratio of thick to thin filaments is 1 : 3. Each thick filament is surrounded by 6 thin filaments in a hexagonal arrangement. The length of the sarcomere of each myofibril is significantly shorter and diameter of the myofibrils significantly smaller in long-winged than in short-winged morphs. However, the thick filaments in the long-winged morph are denser than those in the short-winged morph. Furthermore, in the long winged morph there are a greater number of mitochondria than in the short-winged morph. These differences correspond with the fact that long-winged crickets are stronger fliers than short-winged crickets.
Highlights
There are two morphs of Gryllus firmus (Orthoptera: Gryllidae), the sand cricket, which lives in the southeastern United States, a long-winged (LW) morph, some of which are capable of flight and a short-winged (SW) morph that is obligatorily flightless (Veazy et al, 1976)
The structure of insect flight muscles can be used for determining their migration status
As for muscle contraction, Pringle (1981) states that the intensity of muscle contractions is directly related to the orderliness of the arrangement of filaments and inversely related to the ratio of thick filaments to thin
Summary
Flight muscle is one of the most widely studied flight-related tissues in insects mainly because of the variation in the metabolic activity of the different types of muscle (Sacktor, 1970; Usherwood, 1975, Mentel et al, 2003). All muscles receive excitatory innervation from glutamatergic neurons, inhibitory innervation from GABAergic neurons and modulatory innervation from octopaminergic dorsal unpaired median (DUM) neurons (Biserova & Pfluger, 2004). Energy for flight is provided primarily by the very high levels of glucose and lipid in the blood. Adipokinetic hormone (AKH) is very important in the metabolism of lipids and triggers the release of octopamine from octopamine-releasing neurons, such as the DUM neurons (Birkenbeil, 1971), which in turn activates catabolic enzymes, such as lipases and phosphorylases (Fassold et al, 2010)
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