High-frequency calling in Eneopterinae crickets (Orthoptera, Grylloidea, Eneopteridae): adaptive radiation revealed by phylogenetic analysis

Abstract

The dominant frequency (Fd) of the cricket calling song commonly ranges from 2 to 8 kHz because of physical constraints due to small size and stridulum functioning. However some Eneopterinae crickets are known to call with Fds of 10-15 kHz, and one species ( Eneoptera guyanensis ) produces a modulated call with both a low and a high Fd. We studied Fd evolution with respect to phylogeny in the whole Eneopterinae subfamily to reconstruct its pattern of transformation. The phylogenetic pattern resulting from the analysis showed that Fd is relatively stable through the whole clade: the Fd ancestral state (3-7.9 kHz) has been modified only once, with the occurrence of a high Fd in the clade [ Cardiodactylus ( Lebinthus-Agnotecous )]: high Fd replaced low Fd, resulting in high-frequency calling songs. In E. guyanensis , the pattern of frequency change is different: a high Fd component has been added to the low ancestral Fd, resulting in frequency modulation. Investigation of cladogenesis rate indicated that the onset of high Fd in [ Cardiodactylus ( Lebinthus-Agnotecous )] was accompanied by a high cladogenesis rate, supporting a hypothesis of adaptive radiation for high-frequency calling (phylogeny criterion of adaptation). High frequencies are particularly problematic for long-range communication, especially for forest-living species, because of the increase of excess attenuation with frequency. The effectiveness of high-frequency calling is discussed in the clade [ Cardiodactylus ( Lebinthus-Agnotecous )] in relation to the behavioural ecology of the species.