Auditory descending neurons in the prothoracic network of the bush cricket Ancistrura nigrovittata

by Ali Cillov
Doctoral thesis
Date of Examination:2024-01-12
Date of issue:2024-06-20
Advisor:Prof. Dr. Andreas Stumpner
Referee:Prof. Dr. Andreas Stumpner
Referee:Dr. Jan Clemens
Persistent Address: http://dx.doi.org/10.53846/goediss-10555

 

 

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Abstract

English

Ancistrura nigrovittata is a duetting phaneropterine bush cricket species. Males sing with a fixed temporal and spectral pattern, the characteristics of which are important for recognition; females reply to the song with a low latency click (~30 ms). Auditory neurons in the brain have longer spike latencies. Neurons descending from the ear to the wings, gated by a pattern recognition network in the brain, could trigger the female reply directly. Therefore, I investigated the population of descending neurons (DN) in the prothorax, the first level of central auditory processing. I characterised multiple morphological and physiologically distinct neuron subtypes, some of which have not been previously reported. Lateral DN have weak or no auditory response and are mostly vibratory. These constitute the majority of previous reports in ensiferans. A local descending neuron is structurally similar to other DN but is intraganglionic. It responds to a broad range of frequencies and temporal patterns and could function as a reference neuron. Bushy DN are tuned to frequencies around 20 kHz (peak frequency of the calling song). This group is composed of diverse neurons with only subtle anatomical differences. Another DN is both morphologically and in its sensory responses a mixture of lateral and bushy DN: sensitive to both vibration and sound. It could play a role in near field multimodal courtship behaviour. Using data from behavioural observations conducted by a collaborator, I describe the nearfield communication of A. nigrovittata. It consists of a complex combination of vibration and sound with a consistent use of simultaneous acoustic and vibratory signals when the animals are within close proximity of each other. One DN I describe in the current study could underlie this multimodal behaviour. Overall, I characterise the last unexplored major group in the local auditory processing network of a species that has been intensively studied. There is a significant stream of descending data with no known function, as well as integration of multiple modalities already on a local level. These findings highlight our limited knowledge about insect sensory processing and the importance of pre-brain areas in distributed nervous systems.
Keywords: hearing; Orthoptera; interneuron; bushcricket; electrophysiology; communication
 
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