Two matched filters and the evolution of mating signals in four species of cricket

Abstract

BackgroundMale field crickets produce pure-tone calling songs to attract females. Receivers are expected to have evolved a "matched filter" in the form of a tuned sensitivity for this frequency. In addition, the peripheral directionality of field crickets is sharply tuned as a result of a pressure difference receiver. We studied both forms of tuning in the same individuals of four species of cricket, where Gryllus bimaculatus and G. campestris are largely allopatric, whereas Teleogryllus oceanicus and T. commodus occur also sympatrically.ResultsThe sharpness of the sensitivity filter is highest for T. commodus, which also exhibits low interindividual variability. Individual receivers may also vary strongly in the best frequency for directional hearing. In G. campestris, such best frequencies occur even at frequencies outside the range of carrier frequencies of males. Contrary to the predictions from the "matched filter hypothesis", in three of the four species the frequency optima of the two involved filters are not matched to each other, and the mismatch can amount to 1.2 kHz. The mean carrier frequency of the male population is between the frequency optima of both filters in three species. Only in T. commodus we found a match between both filters and the male carrier frequency.ConclusionOur results show that a mismatch between the sensitivity and directionality tuning is not uncommon in crickets, and an observed match (T. commodus) appears to be the exception rather than the rule. The data suggests that independent variation of both filters is possible. During evolution each sensory task may have been driven by independent constraints, and may have evolved towards its own respective optimum.

Matching sender and receiver: poikilothermy and frequency tuning in a tree cricket

“…This would depend on ecological context; for example, a mismatch may not pose significant difficulty for the female if the conspecific CF is quite different from the sympatric acoustic community. Such mismatches in frequency tuning both slight and extreme have indeed been reported in insects (Bailey and Römer, 1991;Mason et al, 1999;Kostarakos et al, 2008;Kostarakos et al, 2009) and anurans (Gerhardt and Mudry, 1980).…”

“…Membrane resonances in field crickets are centred on the conspecific song CF (Fig.7) (Paton et al, 1977;Larsen and Michelsen, 1978) and act as a first-level filter applied to the impinging sounds, enhancing the representation of conspecific calls (Oldfield et al, 1986;Kostarakos et al, 2008;Kostarakos et al, 2009). These filter characteristics are believed to remain the same for a direct external input to the tympanum as well as for the internal tracheal input to the cricket ear (Robert, 2005), as the resonant properties of the tympanum are considered to mainly result from intrinsic material characteristics.…”

“…However, the two frequency filters in the field cricket system are only sometimes matched with each other (Kostarakos et al, 2008;Kostarakos et al, 2009). …”

Low pass filters and differential tympanal tuning in a paleotropical bushcricket with an unusually low frequency call

“…In insects, this correspondence is often achieved by exploiting the resonant properties of the auditory system. Such a match can be seen in the receiver's tympanum vibrating with the highest amplitude at the sender's carrier frequency (Lewis et al, The Journal of Experimental Biology 216 (5) 1975; Paton et al, 1977;Larsen and Michelsen, 1978;Michelsen et al, 1994;Nowotny et al, 2010), and is enhanced by an abundantly documented correspondence between the call carrier frequency and the spectral sensitivity of a majority of the receiver's auditory neurons (Nocke, 1975;Zaretsky and Eibl, 1978;Esch et al, 1980;Hill and Oldfield, 1981;Hutchings and Lewis, 1981;Oldfield et al, 1986;Ball et al, 1989;Larsen et al, 1989;Mason et al, 1991;Lin et al, 1993;Stumpner, 1996;Imaizumi and Pollack, 1999;Kostarakos et al, 2009;Hummel et al, 2011;Schmidt et al, 2011).…”

“…The acoustic features of tettigoniid calls have been studied in detail relative to ecological pressures from eavesdropping parasitoid flies (Lakes-Harlan and Heller, 1992;Walker, 1993;Lehmann and Heller, 1998) and predatory bats that use this acoustic information to locate their targets (Tuttle et al, 1985;Belwood and Morris, 1987;Belwood, 1990). Specifically, it has been suggested that low calling activity and the use of pure tones and very high ultrasonic frequencies by neotropical pseudophyllines (Rentz, 1975;Morris and Beier, 1982;Belwood and Morris, 1987;Morris et al, 1989;Morris et al, 1994;Heller, 1995) makes them difficult to localize by mammalian ears (Belwood and Morris, 1987) and limits the spread of the sound due to frequency-dependent attenuation (Morris et al, 1994), thereby reducing detection by mammalian predators (Heller, 1995).…”