The neuroethology of song cessation in response to gleaning bat calls in two species of katydids,Neoconocephalus ensigerandAmblycorypha oblongifolia

Abstract

We investigated whether the use of primary or secondary behavioural defences is related to prey sensory thresholds using two species of North American katydids, Neoconocephalus ensiger and Amblycorypha oblongifolia. Male katydids produce intense calling songs to attract mates, and many gleaning bat species are known to use these calls to locate them as prey. Low duty cycle calling (i.e. sporadic calls) is a primary defence against gleaning bats (prevents attacks), and song cessation is a secondary defence (enables survival of an attack), for which these two species show behavioural differences. Echolocation calls of Myotis septentrionalis, a sympatric gleaning bat species, were broadcast to singing katydids and to neural preparations of these katydids to test if differences in behavioural response were related to differences in auditory sensitivity. We measured thresholds and firing patterns of the T-cell, an auditory interneuron involved in predator detection. We hypothesized that low duty cycle calling is the best defence for species not sensitive enough to mount a secondary defence in response to predator cues; therefore, we predicted that N. ensiger (high duty cycle song) would have lower behavioural and T-cell thresholds than A. oblongifolia (low duty cycle song). Although more N. ensiger ceased singing than A. oblongifolia, the number and maximum firing rate of T-cell action potentials did not differ between species for echolocation call sequences. We suggest that the T-cell has divergent functions within the Tettigoniidae, including predator and mate detection, and the function could be context dependent in some species.