A shift toward harmonics for high-frequency calling shown with phylogenetic study of frequency spectra in Eneopterinae crickets (Orthoptera, Grylloidea, Eneopteridae)

Abstract

Dominant frequency is an important feature of cricket song, as it can be used for species recognition and mate choice. The dominant frequency usually ranges from 2 to 8 kHz and corresponds to the fundamental frequency of the song. In preliminary studies we documented high-frequency songs in the subfamily Eneopterinae. To analyse this phenomenon further, we investigate the spectral properties of these cricket songs. Based on the analysis of the frequency spectra in reference to phylogeny, we show that a shift of dominant frequency from the fundamental toward the second or the third harmonic of the song occurred in the Lebinthini tribe. In this clade the upper harmonics (second or third) become the most powerful frequencies of the song. From an evolutionary point of view, we document a case of convergence toward high-frequency calling between species of Eneoptera Burmeister, 1838, which emit alternatively low and high fundamental frequencies, and the Lebinthini, which emit high frequencies using upper harmonics. Functional hypotheses are discussed to explain how these high frequencies could be produced.Résumé : La fréquence dominante du chant d'appel est une propriété importante chez les grillons, car elle peut intervenir dans la reconnaissance spécifique et le choix des mâles par les femelles. Elle est généralement comprise entre 2 et 8 kHz et correspond à la fréquence fondamentale du chant. Nous avons montré dans des travaux préliminaires que des grillons Eneopterinae émettaient leur chant d'appel dans des fréquences beaucoup plus hautes. Pour préciser ces observations, nous avons analysé le spectre de fréquence du chant d'appel de ces espèces. Sur la base de l'étude des spectres en référence à la phylogénie, nous montrons qu'il s'est produit un glissement de la fréquence dominante chez la tribu Lebinthini. Dans ce clade, les fréquences harmoniques (seconde ou troisième) deviennent plus puissantes que la fréquence fondamentale. D'un point de vue évolutif, nous documentons un cas de convergence vers les hautes fréquences chez des espèces d'Eneoptera Burmeister, 1838, qui émettent alternativement des basses et des hautes fréquences fondamentales, et chez les Lebinthini, qui émettent des hautes fréquences en utilisant les harmoniques. Nous présentons des hypothèses fonctionnelles susceptibles d'expliquer comment ces hautes fréquences sont émises.

Mechanisms of high frequency song generation in brachypterous crickets and the role of ghost frequencies

“…Other peaks of low energy are detected at 15, 23 and 34kHz. This spectral composition is typical of all the previously described songs of Agnotecous species (Robillard et al, 2007;Robillard et al, 2010) and of some Lebinthus species (Robillard, 2009) (supplementary material Fig.S1). …”

“…The Lebinthini crickets consist of a monophyletic tribe that belongs to the subfamily Eneopterinae (Robillard et al, 2007;Nattier et al, 2011). We analysed two species of the subclade of brachypterous Lebinthini, Agnotecous robustus (Chopard 1915) and Lebinthus n. sp.…”

“…Analysed in a phylogenetic framework (Robillard et al, 2007), the main consequence of this pattern is that high frequencies evolved several times from a plesiomorphic low frequency condition where the first peak carried the dominant energy, either through convergence, i.e. independently in the two clades [Cardiodactylus versus (Lebinthus-Agnotecous)], or stepwise, with the dominant energy jumping from one harmonic peak to another.…”

“…Notably, dominant energy is found at the second peak of the spectrum in the 'brachypterous' clade (LebinthusAgnotecous) or at the third peak in the 'long-winged' genus Cardiodactylus, these two clades being sister groups (Fig.2) (Robillard et al, 2007) (see supplementary material Fig.S1 for an illustration of the song spectrum of 12 species showing this spectral composition where the second peak dominates over the first).…”

New Caledonia: a very old Darwinian island?

“…minute and giant species) on an island where other small vertebrates are scarce (Bauer & Sadlier 2000;Bauer et al 2006;Smith et al 2007). Another example is the radiation of the cricket genus Agnotecous ( Eneopterinae), which includes many species with peculiar stridulatory apparatuses that emit songs in unusually high frequencies and with harmonic shifts (Robillard & Desutter-Grandcolas 2004;Robillard et al 2007). The cockroach subfamily Tryonicinae (Blattidae) includes the speciose genus Lauraesilpha, the members of which exhibit a unique combination of Araucaria (Setoguchi et al1998) Angustonicus (Murienne et al 2005) geckos (Bauer et al 2006) Sapotaceae (Bartish et al 2005) Proteaceae (Barker et al 2007) Paratya (Page et al 2005) diving beetles (Balke et al 2007a, b) galaxiid (Waters et al 2000) Tasmantis Scincidae (Smith et al 2007) sandalwoods ( behavioural traits, wood eating, intestinal ciliates and solitary habits (Grandcolas 1997;Murienne 2006; in press a, submitted).…”