Stridulation of acridid grasshoppers after hemisection of thoracic ganglia: evidence for hemiganglionic oscillators

Summary

In the grasshopperChorthippus biguttulus the stridulatory movements of males with surgically manipulated ventral nerve cords were investigated.

• 1. The stridulation pattern of animals with a hemisected mesothoracic ganglion was indistinguishable from that of intact animals.

• 2. After hemisection of the metathoracic ganglion several animals were still able to stridulate in the species-specific pattern (Figs. 3, 5). Different structural elements of the song, however, were affected to different degrees by this operation. Although the stereotyped up-and-down movements were normal, the rhythm of pauses, which in intact animals are inserted after every third to fourth up- and-down cycle, was disturbed. As a result, the variation of syllable lengths was much higher (Fig. 4).

• 3. A prominent feature after hemisection of the metathoracic ganglion was an almost complete loss of coordination between left and right hind legs (Figs. 5–7). Only in the coarse structure of the song (e.g. the beginning and termination of song sequences) was a correlation of the leg movements still discernible. This was especially obvious in songs of the rivalry type and in precopulatory kicking movements (Fig. 8).

• 4. If in addition to hemisection of the metathoracic ganglion one of the neck connectives was transected the animals stridulated only with the hind leg ipsilateral to the intact connective (Fig. 11).

• 5. Even after hemisection of both the meso- and metathoracic ganglia, animals were able to produce the species-specific stridulation pattern (Fig. 9).

• 6. In animals with hemisected metathoracic ganglia and both connectives between pro- and mesothoracic ganglia transected, components of the species-specific pattern could be induced by current injection into the mesothoracic ganglion (Fig. 10).

• 7. These results suggest that the stridulation rhythm-producing neuronal network is composed of hemisegmental subunits. A hemiganglionic structure of rhythm generators might reflect the ancestral organization of locomotion-controlling networks.