© 2017. Published by The Company of Biologists Ltd | Journal of Experimental Biology (2017) 220, 1112-1121 doi:10.1242/jeb.153106 RESEARCH ARTICLE Functional morphology of tegmina-based stridulation in the relict species Cyphoderris monstrosa (Orthoptera: Ensifera: Prophalangopsidae) Benedict D. Chivers1, Olivier Béthoux2, Fabio A. Sarria-S1, Thorin Jonsson1, Andrew C. Mason3 and Fernando Montealegre-Z1,* ABSTRACT stridulation, primarily to attract females. In all cases, at least one Male grigs, bush crickets and crickets produce mating calls by forewing bears a row of teeth, the file, which overlaps the other tegminal stridulation: the scraping together of modified forewings forewing, itself endowed with a scraper (or plectrum), located along functioning as sound generators. Bush crickets (Tettigoniidae) the posterior margin (Pierce, 1948). The plectrum is scraped over and crickets (Gryllinae) diverged some 240 million years ago, with the file in sequence, and the resulting vibrations cause particular each lineage developing unique characteristics in wing morphology wing cells (e.g. harp and mirror) to oscillate and radiate sound and the associated mechanics of stridulation. The grigs (Pierce, 1948; Broughton, 1964; Bailey, 1970; Sales and Pye, 1974; (Prophalangopsidae), a relict lineage more closely related to bush Bennet-Clark, 2003). This elaborate system, known from the crickets than to crickets, are believed to retain plesiomorphic features Triassic period (ca. 220 million years ago; Béthoux, 2012), has been of wing morphology. The wing cells widely involved in sound subject to tremendous evolution, resulting in a wide array of wing production, such as the harp and mirror, are comparatively small, morphologies, body sizes, and behaviour. In some cases forewing- poorly delimited and/or partially filled with cross-veins. Such based sound radiation is enhanced by particular shapes of the morphology is similarly observed in the earliest stridulating pronotum (Morris and Mason, 1995), holes in plant leaves acting as ensiferans, for which stridulatory mechanics remains poorly acoustic baffles (Prozesky-Schulze et al., 1975; Forrest, 1991), understood. The grigs, therefore, are of major importance to particular tegminal inflations (Hemp, 2001; Montealegre-Z and investigate the early evolutionary stages of tegminal stridulation, a Mason, 2005), or burrows purposely shaped for enhancing sound critical innovation in the evolution of the Orthoptera. The aim of this radiation (Bailey et al., 2001; Forrest, 1991). study is to appreciate the degree of specialization on grig forewings, Field and bush crickets represent two main lines of evolution. ∼ through identification of sound radiating areas and their properties. Field crickets (subfamily: Gryllinae; 1100 species according to ∼ – For well-grounded comparisons, homologies in wing venation (and Eades et al., 2016), produce low-frequency calls ( 3 8 kHz) associated areas) of grigs and bush crickets are re-evaluated. Then, (Walker, 1973; Hoy et al., 1982) from visually symmetrical (but using direct evidence, this study confirms the mirror cell, in functionally asymmetrical) wings with multiple, well delimited, association with two other areas (termed ‘neck’ and ‘pre-mirror’), as radiating cells, the largest of which is the harp. The harp is the the acoustic resonator in the grig Cyphoderris monstrosa. Despite primary radiator for the fundamental components of the call, while a the use of largely symmetrical resonators, as found in field crickets, secondary area, the mirror, also contributes to sound production for analogous features of stridulatory mechanics are observed between the high-frequency components, mostly obvious in the courtship C. monstrosa and bush crickets. Both morphology and function in calls (Bennet-clark, 2003; Montealegre-Z et al., 2011a). The grigs represents transitional stages between unspecialized forewings resonance of each of these cells is not affected by manipulation of and derived conditions observed in modern species. the physical properties of the other membranous areas (Bennet- Clark, 2003). Field crickets predominantly have a ‘right-wing-on- KEY WORDS: Laser vibrometry, Bioacoustics, Stridulation, Sound top’ arrangement (Masaki et al., 1987), which is required for generation, Homology, Wing venation stridulation resulting in tonal purity in the produced signals (Elliott and Koch, 1983). The carrier frequency of these calls is dictated by INTRODUCTION an escapement mechanism (Elliott and Koch, 1985; Koch et al., Within the orthopteran suborder Ensifera, males of most bush 1988; Prestwich et al., 2000) and thus reliant on the natural crickets (Tettigoniidae), field crickets (Gryllinae) and a few closely frequency of the harps. Furthermore, coherent vibration of both related species, generate acoustic signals through forewing wings at this resonant frequency is facilitated by a phase-shifting mechanism, which allows oscillatory synchrony between both tegmina (Montealegre-Z et al., 2009). 1Bioacoustics and Sensory Biology Lab, Joseph Banks Laboratories, University of Lincoln, Green Lane, Lincoln LN6 7DL, UK. 2Sorbonne Universités, UPMC Univ Most noticeable about most modern bush crickets (family: Paris 06, MNHN, CNRS, Centre de recherche sur la paléobiodiversitéet les Tettigoniidae, ∼7000 species according to Eades et al., 2016) is the paléoenvironnements (CR2P), 57 Rue Cuvier, CP 38, Paris 75005, France. bilateral asymmetry between the forewings (Dumortier, 1963; 3Integrative Behaviour and Neuroscience, University of Toronto Scarborough, 1265 Military Trail, Scarborough, Ontario, Canada, M1C 1A4. Montealegre-Z and Postles, 2010; Gu et al., 2012; Chivers et al., 2014; Sarria-S et al., 2016; Cole and Chiang, 2016). The major *Author for correspondence ([email protected]) radiating wing cell is named the mirror and is found primarily on the F.M., 0000-0001-5186-2186 right wing, with the functioning file being on the left wing. The mirror is very well delimited, generally composed of the cross-vein Received 9 November 2016; Accepted 4 January 2017 free mirror (purple in Fig. 1D), sometimes in association with a Journal of Experimental Biology 1112 RESEARCH ARTICLE Journal of Experimental Biology (2017) 220, 1112-1121 doi:10.1242/jeb.153106 Fig. 1. Revised topographic homology conjectures for the grigs (Prophalangopsidae) and the bush crickets (Tettigoniidae), compared with the field crickets (Gryllinae). (A,B) Cyphoderris monstrosa (grig; specimen IWC OB 530, left forewing, ventral view), wing venation (A) and areas (B). (C–F) Tettigonia cantans (bush cricket; specimen IWC OB 862, right forewing, dorsal view). (C,D) THC newly proposed herein, wing venation (C) and areas (D). (E,F) THC according to Béthoux (2012), wing venation (E) and areas (F). (G,H) Teleogryllus oceanicus (field cricket; specimen IWC OB 645, right forewing, ventral view flipped horizontally; THC according to Béthoux, 2012), wing venation (G) and areas (H). See Materials and methods for details. second cell (light green in Fig. 1D) (Bailey and Broughton, 1970; et al., 2014; Song et al., 2015; Cole and Chiang, 2016). However, Montealegre-Z and Postles, 2010). In many cases, there exists a similar to field crickets, tegminal stridulation in Cyphoderris spp. mirror on the left wing, and a file on the right wing, but the former is occurs from largely symmetrical forewings (Morris et al., 2002). usually partially damped and filled with cross-veins, and the latter In addition, unlike both field and bush crickets, stridulation in greatly atrophied (Montealegre-Z and Mason, 2005; Montealegre-Z Cyphoderris spp. can be performed with either wing on top, and and Postles, 2010; Chamorro-Rengifo et al., 2014). These also the wings lack some of the well-delimited wing cells, largely morphological wing characteristics result in an obligatory wing free of cross-veins (Morris and Gwynne, 1978; Fig. 1A,B). arrangement of ‘left-over-right’ for stridulatory sound production. Furthermore, Cyphoderris spp. sing at ∼12–15 kHz (Morris and Specific to bush crickets is the widespread use of ultrasonic Gwynne, 1978; Morris et al., 2002), a range higher than that in field frequencies in the calls; indeed ∼70% of species use ultrasounds in crickets (3–8 kHz; Hoy et al., 1982; Otte, 1992) but lower than the range of 20–150 kHz (Morris et al., 1994; Montealegre-Z, 2009; that in most bush crickets (>20 kHz; Montealegre-Z, 2009). In Sarria-S et al., 2014), with some exceptions singing in the sonic summary, Cyphoderris spp. are of major importance to investigate range as low as 600 Hz (Heller, 1995). It has been suggested that the the early evolutionary stages of a critical innovation, at the root production of tonal calls at high ultrasonic frequencies is facilitated of a tremendous diversity. However, little is known about wing by the single radiating structure in this group, whereby there is no function in Cyphoderris spp., and a detailed knowledge of need to synchronize radiating cells on two wings for coherent sound stridulatory mechanics in this group will allow a better generation (Montealegre-Z et al., 2009; Gu et al., 2012). understanding of the forewing biophysics and communication In summary, both lineages exhibit particular modifications with capabilities in both extant relatives and related fossil taxa. respect to the assumed ground plan. Only a handful of extant species Prior to functional analysis we reconsider conjectures of of grigs (family: Prophalangopsidae, eight extant species according