Description of Acoustic Characters and Stridulatory Pars Stridens of Nicrophorus (Coleoptera: Silphidae): A Comparison of Eight North American Species

Insects make use of sound in a variety of behavioral and reproductive contexts. Acoustic signals are known to serve in defense, sexual advertisement, prey location, and in cooperative activities such as offspring care and group foraging. In airborne signals produced by insects, information associated with species identification is often related to the temporal structure of the sound, while spectral quality is more closely associated with intraspecific variation. The Nicrophorine burying beetles (Insecta: Coleoptera: Silphidae) are a group known to produce sound through dorso-ventro stridulation, but the bioacoustics of this group remains understudied. Here, we examine the stridulatory sound produced by eight North American species of Nicrophorus burying beetles, testing the hypothesis that interspecific differences will be encoded in temporal characteristics of the sound, and that signal divergence will be explained by one of three mechanisms: selection as an intraspecific signal, selection for interspecific aposematism, or random divergence through drift. We digitally recorded stridulation in each species, and analyzed recordings to describe each in respect to four spectral and eight temporal acoustic characters. All species produced a low amplitude biphastic sound pulse consisting of from 58 to 126 syllables, and exhibiting weak dominant frequencies (5.8-12.7 kHz). Collapsing the 12 variables into three rotated factors using principal component analysis, we found no sex-related differences in sound, but significant interspecies divergence in respect to all three factors. We constructed a phylogeny for the group based on the morphology of the stridulatory structures and the acoustic characters, and found weak support for an intraspeci_c signal divergence model.