A noisy neighbour: acoustic competition drives changes in song traits and spatiotemporal behaviour of orthopterans

Competition for acoustic space is key for sound-communicating animals, yet little is known about whether and how it may drive evolutionary pathways, for example signal structure, as well as species distributions or individual spatial behaviour. Here we assessed the occurrence of interspecific acoustic competition in sound-communicating taxa by testing three nonmutually exclusive hypotheses explaining variability of song structure and singing activity, in two sibling species of tree crickets of the genus Oecanthus. By comparing song acoustic parameters, diel activity patterns and relative densities of singing crickets in both sympatry and allopatry, we found that the local co-occurrence of the two species drives changes in all the considered factors of song production. Namely, we report changes in temporal and structural song traits, as well as in singing activity patterns and apparent population density, with strongly asymmetrical effects, only evident for one of the two species considered. Our results highlight the role of acoustic space as a key resource that shapes biotic interactions, and eventually behaviours, in sound-communicating taxa, and represent a replicable approach in the study of acoustic assemblages.