The structure of calling songs in the cicada Pauropsalta annulata Goding and Froggatt (Hemiptera: Cicadidae): evidence of diverging populations?

Variation recorded within species is often taken to represent evidence for local and ongoing adaptation, but often without the interpopulation variation being subject to analysis across the geographic distribution occupied by the taxon. Here we investigate the rhythmic song structure across the range of three known song types in a variable cicada, Pauropsalta annulata Goding and Froggatt. Statistical analysis of the structure of songs across individuals reveals four discrete clusters that are demonstrated to be independent and stable across extensive geographic space in areas of allopatry and, generally, also into areas of sympatry. This suggests that P. annulata is a cryptic species complex. Unique combinations of plant species are linked with each of the clusters, suggesting that the different populations have independent plant associations. These findings are discussed in relation to similar case studies on cicadas and other organisms, with particular emphasis on the most appropriate approach to testing variation across populations, especially when it is thought to represent populations in the initial stages of evolutionary divergence.