Behavioural and neural studies of male singing and female phonotaxis behaviour in crickets

Acoustic communication in crickets is achieved by the production of calling, courtship, and rivalry songs in male crickets and the recognition of the songs by conspecifics. Male crickets sing by rhythmically opening and closing the forewings to generate sound pulses and song patterns. The central command for singing is controlled by the brain. The song structure is under control of the abdominal central pattern generator (CPG) and acts as a behavioural barrier to prevent courtship with females of closely related species. Therefore, an analysis of the song structure, the central command, and the organisation of the CPG in different cricket species could reveal how evolution shaped cricket singing behaviour. In G. bimaculatus, I recorded different song types and corresponding wing movement of individual males. I discovered a small amplitude oscillation of the forewings during courtship song that was not reported before. The similar pulse parameters and wing movements during calling and rivalry song could imply a shared neural network for the two song types in G. bimaculatus. I analysed rivalry and courtship behaviour before and after applying specific lesions to the abdominal nerve cord in G. bimaculatus. Most elements of rivalry and courtship behaviour are not affected by lesions, except for rivalry song, courtship song, and copulation. For generation of the rivalry song the central nerve cord from the brain to A4 is sufficient (same as calling song), whereas the whole nerve cord without the terminal abdominal ganglion is required for generation of courtship song. I compared the calling song before and after applying specific lesions to the abdominal nerve cord in four cricket species: G. rubens, G. assimilis, Teleogryllus oceanicus, and T. commodus. The four species show similar effects of the lesions on the generation of sound pulses besides a species-specific control of song structure, suggesting they share a conserved organisation of the CPG network for calling song. Following the discovery of the calling song command neuron in G. bimaculatus, I carried out intracellular recording in the brain of males of different species. I found the putative command neurons for calling song in G. bimaculatus, G. assimilis, and T. commodus and characterize the physiological and functional properties of these neurons. The results suggest the command neurons in the three species could be homologues by showing a similar control on generating calling song. Furthermore, based on female cricket phonotaxis preference I developed an animal acoustic selecting system, in which the females have to navigate through a complex parkour to reach the acoustic stimulus presenting speaker. I tested the system with different selecting experiments and proved the system can be applied to select females attracted to certain song pattern. Overall, these findings broaden our understanding of cricket singing in terms of neural control of different song types and evolution of singing behaviour in different species, and provide a new tool to study phonotactic behaviour.Cambridge Trust Ministry of Education in Taiwa

Lesions of abdominal connectives reveal a conserved organization of the calling song central pattern generator (CPG) network in different cricket species.

Although crickets move their front wings for sound production, the abdominal ganglia house the network of the singing central pattern generator. We compared the effects of specific lesions to the connectives of the abdominal ganglion chain on calling song activity in four different species of crickets, generating very different pulse patterns in their calling songs. In all species, singing activity was abolished after the connectives between the metathoracic ganglion complex and the first abdominal ganglion A3 were severed. The song structure was lost and males generated only single sound pulses when connectives between A3 and A4 were cut. Severing connectives between A4 and A5 had no effect in the trilling species, it led to an extension of chirps in a chirping species and to a loss of the phrase structure in two Teleogryllus species. Cutting the connectives between A5 and A6 caused no or minor changes in singing activity. In spite of the species-specific pulse patterns of calling songs, our data indicate a conserved organisation of the calling song motor pattern generating network. The generation of pulses is controlled by ganglia A3 and A4 while A4 and A5 provide the timing information for the chirp and/or phrase structure of the song