Morphological determinants of signal carrier frequency in katydids (Orthoptera): a comparative analysis using biophysical evidence of wing vibration

Abstract

Male katydids produce mating calls by stridulation using specialized structures on the forewings. The right wing (RW) bears a scraper connected to a drum-like cell known as the mirror and a left wing (LW) that overlaps the RW and bears a serrated vein on the ventral side, the stridulatory file. Sound is generated with the scraper sweeping across the file, producing vibrations that are amplified by the mirror. Using this sound generator, katydids exploit a range of song carrier frequencies (CF) unsurpassed by any other insect group, with species singing as low as 600 Hz and others as high as 150 kHz. Sound generator size has been shown to scale negatively with CF, but such observations derive from studies based on few species, without phylogenetic control, and/or using only the RW mirror length. We carried out a phylogenetic comparative analysis involving 94 species of katydids to study the relationship between LW and RW components of the sound generator and the CF of the male's mating call, while taking into account body size and phylogenetic relationships. The results showed that CF negatively scaled with all morphological measures, but was most strongly related to components of the sound generation system (file, LW and RW mirrors). Interestingly, the LW mirror (reduced and nonfunctional) predicted CF more accurately than the RW mirror, and body size is not a reliable CF predictor. Mathematical models were verified on known species for predicting CF in species for which sound is unknown (e.g. fossils or museum specimens)

Ultrasonic songs and stridulum anatomy of Asiophlugis crystal predatory katydids (Tettigonioidea: Meconematinae: Phlugidini)

“…This has been observed in the Aerotegmina katydids (e.g., Heller and Hemp 2018). Carrier frequency is mainly dictated by the resonator anatomy (mirror and harp but see; Montealegre-Z and Postles 2010; Montealegre-Z 2012; Montealegre-Z et al 2017).…”

“…The songs of Phlugidini are similar in that they are entirely ultrasonic, supporting the fact that Meconematinae species usually employ ultrasonic calls (Helfert and Sänger 1998;Montealegre-Z et al 2006Montealegre-Z et al , 2017Chamorro-Rengifo et al 2014;Chamorro-Rengifo and Braun 2016;Sarria-S et al 2017). A. rete (A. thai junior synonym) sings at frequencies between 30 and 50 kHz (Helfert and Sänger 1998) and neotropical species such as Phlugis ocraceovittata Piza, 1960 also sings at frequencies between 40 and 60 kHz (Chamorro-Rengifo and Braun 2016).…”

Testing the role of trait reversal in evolutionary diversification using song loss in wild crickets

“…4 provides examples. Our main analysis focused on the harp area of the wing as it is a key determinant of the carrier frequency of male song in ensiferan insects (22). Table 2 reports the peak resonance of the harp (or vestigial harp) for each measured individual.…”

“…Research examining acoustic signal function and diversity in ensiferan singing insects (crickets and katydids) has mostly focused on the behavioral components of song (i.e., the pattern of sound pulses produced during wing movement) (19,20). However, a major source of variation in acoustic signals is their carrier frequency, which is increasingly recognized as an important signal feature distinguishing closely related species (21,22). Frequency is primarily determined by the morphology of soundresonating structures (23,24), and can be varied by mechanically shifting between different resonant modes in some species (25)(26)(27).…”

Paraplangia sinespeculo, a new genus and species of bush-cricket, with notes on its biology and a key to the genera of Phaneropterinae (Orthoptera: Tettigonioidea) from Madagascar

“…The mirror is an important structure for sound radiation and is considered as typical for bushcrickets (e.g. Montealegre-Z et al 2017). However, its systematic distribution and size have never been studied in detail.…”