Biochemical aspects of flight and flightlessness in Gryllus: flight fuels, enzyme activities and electrophoretic profiles of flight muscles from flight-capable and flightless morphs
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Abstract
Female Gryllus assimilis subjected to 4.5-7.7h continuous tethered flight had significantly
lower amounts of total lipid, triglyceride and total soluble carbohydrate compared
with unflown controls. A much greater amount of total lipid (6.3mg) was used during
flight compared with carbohydrate (0.14mg). Flown individuals also had substantially
reduced amounts of injected, radiolabeled [(14)C]-oleic acid. Activities of lipid,
carbohydrate and amino acid catabolizing enzymes in flight muscles of G. assimilis
and its wing-polymorphic congener, G. firmus, were very similar to activities in insects
which primarily utilize lipid to power flight. By contrast, enzyme activities were
very different from those in insects which primarily or exclusively use carbohydrate
or proline as a flight fuel. These results strongly implicate lipid as the major flight
fuel in Gryllus. Previous studies have shown that lipid levels are higher in flight-capable
(long-winged) G. firmus that have small ovaries compared with flightless (short-winged)
females that have large ovaries. Results of the present and previous studies collectively
indicate that elevated lipid in long-winged G. firmus represents an energetic cost
of flight capability which reduces (trade-offs with) reproduction in Gryllus. In G.
firmus, mass-specific activities of nearly all enzymes were considerably reduced in
underdeveloped, and to a lesser degree in histolyzed muscle, compared with fully-developed
flight muscle. An important exception was alanine aminotransferase, whose activity
was the highest in histolyzed muscle, and which may be involved in the catabolism
of amino acids derived from muscle degradation. Despite the dramatic differences in
enzyme activity, electrophoretic profiles of soluble flight-muscle proteins differed
only subtly between fully-developed and underdeveloped or histolyzed flight muscles.