Male age and female mate choice in a synchronizing katydid

Multielectrode array use in insect auditory neuroscience to unravel the spatio-temporal response pattern in the prothoracic ganglion of Mecopoda elongata

Mechanoreceptors in hearing organs transduce sound-induced mechanical responses into neuronal signals, which are further processed and forwarded to the brain along a chain of neurons in the auditory pathway. Bushcrickets (katydids) have their ears in the front leg tibia, and the first synaptic integration of sound-induced neuronal signals takes place in the primary auditory neuropil of the prothoracic ganglion. By combining intracellular recordings of the receptor activity in the ear, extracellular multichannel array recordings on top of the prothoracic ganglion and hook electrode recordings at the neck connective, we mapped the timing of neuronal responses to tonal sound stimuli along the auditory pathway from the ears towards the brain. The use of the multielectrode array allows the observation of spatio-temporal patterns of neuronal responses within the prothoracic ganglion. By eliminating the sensory input from one ear, we investigated the impact of contralateral projecting interneurons in the prothoracic ganglion and added to previous research on the functional importance of contralateral inhibition for binaural processing. Furthermore, our data analysis demonstrates changes in the signal integration processes at the synaptic level indicated by a long-lasting increase in the local field potential amplitude. We hypothesize that this persistent increase of the local field potential amplitude is important for the processing of complex signals, such as the conspecific song.

Rhythm Generation and Rhythm Perception in Insects: The Evolution of Synchronous Choruses

Insect sounds dominate the acoustic environment in many natural habitats such as rainforests or meadows on a warm summer day. Among acoustic insects, usually males are the calling sex; they generate signals that transmit information about the species-identity, sex, location, or even sender quality to conspecific receivers. Males of some insect species generate signals at distinct time intervals, and other males adjust their own rhythm relative to that of their conspecific neighbors, which leads to fascinating acoustic group displays. Although signal timing in a chorus can have important consequences for the calling energetics, reproductive success and predation risk of individuals, still little is known about the selective forces that favor the evolution of insect choruses. Here, we review recent advances in our understanding of the neuronal network responsible for acoustic pattern generation of a signaler, and pattern recognition in receivers. We also describe different proximate mechanisms that facilitate the synchronous generation of signals in a chorus and provide examples of suggested hypotheses to explain the evolution of chorus synchrony in insects. Some hypotheses are related to sexual selection and inter-male cooperation or competition, whereas others refer to the selection pressure exerted by natural predators. In this article, we summarize the results of studies that address chorus synchrony in the tropical katydid Mecopoda elongata, where some males persistently signal as followers although this reduces their mating success.