Courtship Songs of Green Lacewings Filmed in Slow Motion: How a Simple Vibrating Structure can Generate Complex Signals (Neuroptera: Chrysopidae: Chrysoperla)

Abstract

All of the cryptic species in the Chrysoperla carnea-group of green lacewings produce substrate-borne duetting songs by vibrating the abdomen up and down. Here, we examine the motion of the abdomen during song production using a high-speed video camera. Through temporal (oscillogram) and frequency (sonogram) analysis, these motions are compared to the vibrational signals recorded from the substrate. In tests of three focal and seven non-focal species, we find that the movement of the abdomen follows a path that induces complex oscillations in lightweight substrates. Although the waveform of the signal in the substrate does not exactly mirror the waveform of abdominal motion, the frequencies of the two waveforms are nevertheless identical. In all species, the abdomen is driven by neuromuscular elements that simultaneously generate two or more signals (tones) of different frequency within the abdomen. Comparison in different species of how the abdomen moves when producing these distinct tones potentially allows us to detect homologous song elements across the carnea-group, thus clarifying some patterns of song evolution in this rapidly evolving clade.