Consequences of anthropogenic noise when conflicting with sexually selected acoustic signals

The signalling systems of species throughout the Animal Kingdom are at risk of disruption from human disturbances. Anthropogenic noise is a prominent acoustic pollutant in many environments and is known to conflict with the acoustic sexual signalling systems of both terrestrial and aquatic animals. However, the consequences and causes of such a conflict largely remain unknown, especially in invertebrate species. The experiments I present in this thesis highlight the behavioural and physiological consequences of anthropogenic noise when conflicting with an insect’s acoustic signals. Additionally, I also consider the acoustic characteristics necessary in any given stimulus to cause such a disruption. To measure these consequences, I observed the sexual signalling systems of the Mediterranean field cricket, Gryllus bimaculatus, under conditions of anthropogenic noise and conducted behavioural, acoustic, and physiological analyses. I found the acoustic signal used to detect the location of a signalling individual (the ‘calling song’) suffered reduced reception under anthropogenic noise conditions, shown by a reduction in female responses. Additionally, I also found the acoustic signal used during courtship displays (the ‘courtship song’) sustained reduced signal transmission, as males signalled less, and reduced signal perception, as females failed to distinguish between high and low ‘quality’ songs. However, aggressive encounters between two males, which feature an acoustic signal (the ‘aggressive song’), remained stable under similar acoustic conditions. Physiological analyses revealed potential energetic costs related to acoustic signals that had been altered to combat disruption from anthropogenic noise. Furthermore, the differences I observed between noise conditions highlighted the acoustic characteristic that are important in causing this disruption. The results I present in this thesis detail the deleterious consequences of anthropogenic noise disrupting invertebrate sexual signalling systems, both in terms of behaviour and energetic costs. Additionally, I discuss the variability in signals that may be disrupted by anthropogenic noise conditions and the acoustic characteristics that drive this disruption in the first place. This further cements anthropogenic disturbances as a new and dangerous selection pressure facing many animal populations.