Functional morphology of tegmina-based stridulation in the relict speciesCyphoderris monstrosa(Orthoptera: Ensifera: Prophalangopsidae)

Abstract

Male grigs, bush crickets and crickets produce mating calls by tegminal stridulation: the scraping together of modified forewings functioning as sound generators. Bush crickets (Tettigoniidae) and crickets (Gryllinae) diverged some 240 million years ago, with each lineage developing unique characteristics in wing morphology and the associated mechanics of stridulation. The grigs (Prophalangopsidae), a relict lineage more closely related to bush crickets than to crickets, are believed to retain plesiomorphic features of wing morphology. The wing cells widely involved in sound production, such as the harp and mirror, are comparatively small, poorly delimited and/or partially filled with cross-veins. Such morphology is similarly observed in the earliest stridulating ensiferans, for which stridulatory mechanics remains poorly understood. The grigs, therefore, are of major importance to investigate the early evolutionary stages of tegminal stridulation, a critical innovation in the evolution of the Orthoptera. The aim of this study is to appreciate the degree of specialization on grig forewings, through identification of sound radiating areas and their properties. For well-grounded comparisons, homologies in wing venation (and associated areas) of grigs and bush crickets are re-evaluated. Then, using direct evidence, this study confirms the mirror cell, in association with two other areas (termed 'neck' and 'pre-mirror'), as the acoustic resonator in the grig Cyphoderris monstrosa. Despite the use of largely symmetrical resonators, as found in field crickets, analogous features of stridulatory mechanics are observed between C. monstrosa and bush crickets. Both morphology and function in grigs represents transitional stages between unspecialized forewings and derived conditions observed in modern species.

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

“…The left mirror on the other hand has maintained a more conservative structure than the right mirror. Whereas the left mirror is atrophied in most species studied so far (Montealegre‐Z & Postles, ; Montealegre‐Z, ; Sarria‐S et al ., , ; Chivers et al ., ; F. Montealegre‐Z, unpublished data), the right mirror underwent selection pressures for frequency diversity based on diversified resonances. Although some left mirrors do contain extra vibrating areas, these remain small and inclusion of these has a minor impact on CF.…”

“…In extinct hagloids (including Haglidae and Prophalangopsidae), the mirrors on left and right tegmina are not as well defined as in modern tettigonids and vibratory patterns of the wings are variable (Chivers et al ., ). Hence, using mirror dimension to estimate CF proves challenging.…”

“…All values were transformed to be positive, irrespective of whether higher or lower values were calculated. Recent evidence (Chivers et al ., ) suggests a functional role for the harp area alongside the mirror region of the wing. Therefore, we additionally calculated the difference between actual and predicted CF of the right and left mirrors, with and without the harp region included.…”

“…(a) Modified from Chivers et al . (), (b) modified from Sarria‐S et al . (), (c) F. Montealegre‐Z (unpublished data).…”

“…1) (Broughton, 1964;Bailey, 1967;Montealegre-Z & Postles, 2010). Katydid males possess mirror cells on both wings; the mirror on the RW is functional in most species, whereas the LW mirror (the wing where the active file resides) is usually atrophied and damped to vibrations (Montealegre-Z & Postles, 2010;Montealegre-Z, 2012;Sarria-S et al, 2016;Chivers et al, 2017). However, in some species, small wing cells associated with the mirror of both wings do exhibit vibrational properties during sound production (Sarria-S et al, 2016).…”