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Biol Bull 141: 434-448. (December 1971)
© 1971 Marine Biological Laboratory
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HIGH FREQUENCY MUSCLES USED IN SOUND PRODUCTION BY A KATYDID. II. ULTRASTRUCTURE OF THE SINGING MUSCLES

HUGH Y. ELDER 1

1 Institute of Physiology, The University of Glasgow, Glasgow, W.2., Scotland and Marine Biological Laboratory, Woods Hole, Massachusetts 02543

1. The forewings of male Neoconocephalus robustus are rubbed together at frequencies of 150-200 Hz during singing. The ultrastructural organization of the mesothoracic flight muscles is typical of synchronous flight muscle.

2. The small diameter fibers (10-25 µ) are well supplied with tracheole branches which invaginate at the Z-lines. The radially arranged, ribbon-like fibrils are only 200-400 nm across.

3. Numerous, large mitochondria (44% of total fiber volume) have tightly packed cristae indicative of a high metabolic activity in these muscles. The cristae were observed in two configurations, normal and vesiculated.

4. The well developed sarcoplasmic reticulum occupies 19% of the total fiber volume and has a surface area 14 µ2/µ3 of fiber. It completely invests the fibrils.

5. T-tube invaginations (incidence, 1 per µ2 fiber surface) form dyads with the sarcoplasmic reticulum at the overlap regions of thick and thin filaments in each sarcomere. The thin: thick filament ratio is 3:1 as in other insect flight muscles. Thick filaments penetrate some distance into the broad Z-lines in contracted specimens.

6. Ultrastructural features of this very fast acting synchronous muscle have been compared with those of other described fast acting muscles and with other katydid flight muscles.

7. The ultrastructure of the singing flight muscles of N. ensiger which employs a wing frequency of 10-15 Hz during singing shows no striking differences from the singing flight muscles of N. robustus; the synchronous flight muscle is probably pre-adapted to a fast contraction/relaxation cycle and the greatest specialization may lie in the central nervous pacemaker and other neural characteristics.




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