02751nas a2200145 4500008004100000245014200041210006900183260001600252300001100268490000600279520222300285100002502508700001902533856005302552 2011 eng d00aSolutions to the Cocktail Party Problem in Insects: Selective Filters, Spatial Release from Masking and Gain Control in Tropical Crickets0 aSolutions to the Cocktail Party Problem in Insects Selective Fil cJun-12-2011 ae285930 v63 a

Background

Insects often communicate by sound in mixed species choruses; like humans and many vertebrates in crowded social environments they thus have to solve cocktail-party-like problems in order to ensure successful communication with conspecifics. This is even more a problem in species-rich environments like tropical rainforests, where background noise levels of up to 60 dB SPL have been measured.

Principal Findings

Using neurophysiological methods we investigated the effect of natural background noise (masker) on signal detection thresholds in two tropical cricket species Paroecanthus podagrosus and Diatrypa sp., both in the laboratory and outdoors. We identified three ‘bottom-up’ mechanisms which contribute to an excellent neuronal representation of conspecific signals despite the masking background. First, the sharply tuned frequency selectivity of the receiver reduces the amount of masking energy around the species-specific calling song frequency. Laboratory experiments yielded an average signal-to-noise ratio (SNR) of −8 dB, when masker and signal were broadcast from the same side. Secondly, displacing the masker by 180° from the signal improved SNRs by further 6 to 9 dB, a phenomenon known as spatial release from masking. Surprisingly, experiments carried out directly in the nocturnal rainforest yielded SNRs of about −23 dB compared with those in the laboratory with the same masker, where SNRs reached only −14.5 and −16 dB in both species. Finally, a neuronal gain control mechanism enhances the contrast between the responses to signals and the masker, by inhibition of neuronal activity in interstimulus intervals.

Conclusions

Thus, conventional speaker playbacks in the lab apparently do not properly reconstruct the masking noise situation in a spatially realistic manner, since under real world conditions multiple sound sources are spatially distributed in space. Our results also indicate that without knowledge of the receiver properties and the spatial release mechanisms the detrimental effect of noise may be strongly overestimated.

1 aSchmidt, Arne, K. D.1 aRömer, Heiner uhttps://dx.plos.org/10.1371/journal.pone.002859302555nas a2200205 4500008004100000245012700041210006900168520186800237653002102105653002302126653001402149653002202163653000902185100002702194700002002221700002202241700002102263700001902284856004602303 2003 eng d00aSerial hearing organs in the atympanate grasshopper Bullacris membracioides (Orthoptera, Pneumoridae)0 aSerial hearing organs in the atympanate grasshopper iBullacris m3 a

In different insect taxa, ears can be found on virtually any part of the body. Comparative anatomy and similarities in the embryological development of ears in divergent taxa suggest that they have evolved multiple times from ubiquitous stretch or vibration receptors, but the homology of these structures has not yet been rigorously tested. Here we provide detailed analysis of a novel set of hearing organs in a relatively “primitive” atympanate bladder grasshopper (Bullacris membracioides) that is capable of signaling acoustically over 2 km. We use morphological, physiological, and behavioral experiments to demonstrate that this species has six pairs of serially repeated abdominal ears derived from proprioceptive pleural chordotonal organs (plCOs). We demonstrate continuity in auditory function from the five posterior pairs, which are simple forms comprising 11 sensilla and resembling plCOs in other grasshoppers, to the more complex anterior pair, which contains 2000 sensilla and is homologous to the single pair of tympanate ears found in “modern” grasshoppers. All 12 ears are morphologically differentiated, responsive to airborne sound at frequencies and intensities that are biologically significant (tuned to 1.5 and 4 kHz; 60–98 dB SPL), and capable of mediating behavioral responses of prospective mates. These data provide evidence for the transition in function and selective advantage that must occur during evolutionary development of relatively complex organs from simpler precursors. Our results suggest that ancestral insects with simple atympanate pleural receptors may have had hearing ranges that equal or exceed those of contemporary insects with complex tympanal ears. Moreover, auditory capability may be more prevalent among modern insect taxa than the presence of overt tympana indicates

10aacoustic insects10aauditory evolution10aCaelifera10achordotonal organ10aears1 avan Staaden, Moira, J.1 aRieser, Michael1 aOtt, Swidbert, R.1 aPabst, Maria, A.1 aRömer, Heiner uhttp://doi.wiley.com/10.1002/cne.v465%3A402531nas a2200133 4500008004100000245007900041210006900120520206600189100002902255700002302284700001902307700001802326856005302344 2008 eng d00aMatched Filters, Mate Choice and the Evolution of Sexually Selected Traits0 aMatched Filters Mate Choice and the Evolution of Sexually Select3 a

Background: Fundamental for understanding the evolution of communication systems is both the variation in a signal and how this affects the behavior of receivers, as well as variation in preference functions of receivers, and how this affects the variability of the signal. However, individual differences in female preference functions and their proximate causation have rarely been studied.

Methodology/Principal Findings: Calling songs of male field crickets represent secondary sexual characters and are subject to sexual selection by female choice. Following predictions from the ‘‘matched filter hypothesis’’ we studied the tuning of an identified interneuron in a field cricket, known for its function in phonotaxis, and correlated this with the preference of the same females in two-choice trials. Females vary in their neuronal frequency tuning, which strongly predicts the preference in a choice situation between two songs differing in carrier frequency. A second ‘‘matched filter’’ exists in directional hearing, where reliable cues for sound localization occur only in a narrow frequency range. There is a strong correlation between the directional tuning and the behavioural preference in no-choice tests. This second ‘‘matched filter’’ also varies widely in females, and surprisingly, differs on average by 400 Hz from the neuronal frequency tuning.

Conclusions/Significance: Our findings on the mismatch of the two ‘‘matched filters’’ would suggest that the difference in these two filters appears to be caused by their evolutionary history, and the different trade-offs which exist between sound emission, transmission and detection, as well as directional hearing under specific ecological settings. The mismatched filter situation may ultimately explain the maintenance of considerable variation in the carrier frequency of the male signal despite stabilizing selection.

1 aKostarakos, Konstantinos1 aHartbauer, Manfred1 aRömer, Heiner1 aTregenza, Tom uhttps://dx.plos.org/10.1371/journal.pone.000300502304nas a2200181 4500008004100000245008200041210006900123520165300192653002701845653001601872653001201888653002401900653002001924100002501944700001401969700001901983856012002002 2011 eng d00aHigh background noise shapes selective auditory filters in a tropical cricket0 aHigh background noise shapes selective auditory filters in a tro3 a

Because of call frequency overlap and masking interference, the airborne sound channel represents a limited resource for communication in a species-rich cricket community like the tropical rainforest. Here we studied the frequency tuning of an auditory neuron mediating phonotaxis in the rainforest cricket Paroecanthus podagrosus, suffering from strong competition, in comparison with the same homologous neuron in two species of European field crickets, where such competition does not exist. As predicted, the rainforest species exhibited a more selective tuning compared with the European counterparts. The filter reduced background nocturnal noise levels by 26 dB, compared with only 16 and 10 dB in the two European species. We also quantified the performance of the sensory filter under the different filter regimes by examining the representation of the species-specific amplitude modulation of the male calling song, when embedded in background noise. Again, the filter of the rainforest cricket performed significantly better in terms of representing this important signal parameter. The neuronal representation of the calling song pattern within receivers was maintained for a wide range of signal-to-noise ratios because of the more sharply tuned sensory system and selective attention mechanisms. Finally, the rainforest cricket also showed an almost perfect match between the filter for sensitivity and the peripheral filter for directional hearing, in contrast to its European counterparts. We discuss the consequences of these adaptations for intraspecific acoustic communication and reproductive isolation between species.

10aacoustic communication10acompetition10acricket10adirectional hearing10aMatched filters1 aSchmidt, Arne, K. D.1 aRiede, K.1 aRömer, Heiner uhttp://jeb.biologists.org/cgi/doi/10.1242/jeb.053819https://syndication.highwire.org/content/doi/10.1242/jeb.05381902436nas a2200229 4500008004100000022001400041245008800055210006900143260001600212300001600228490000800244520157900252653002701831653001901858653002701877653002901904653002001933653002301953100002501976700001902001856018602020 2016 eng d a0022-094900aFunctional relevance of acoustic tracheal design in directional hearing in crickets0 aFunctional relevance of acoustic tracheal design in directional  cMar-10-2017 a3294 - 33000 v2193 a

Internally coupled ears (ICEs) allow small animals to reliably determine the direction of a sound source. ICEs are found in a variety of taxa, but crickets have evolved the most complex arrangement of coupled ears: an acoustic tracheal system composed of a large cross-body trachea that connects two entry points for sound in the thorax with the leg trachea of both ears. The key structure that allows for the tuned directionality of the ear is a tracheal inflation (acoustic vesicle) in the midline of the cross-body trachea holding a thin membrane (septum). Crickets are known to display a wide variety of acoustic tracheal morphologies, most importantly with respect to the presence of a single or double acoustic vesicle. However, the functional relevance of this variation is still not known. In this study, we investigated the peripheral directionality of three co-occurring, closely related cricket species of the subfamily Gryllinae. No support could be found for the hypothesis that a double vesicle should be regarded as an evolutionary innovation to (1) increase interaural directional cues, (2) increase the selectivity of the directional filter or (3) provide a better match between directional and sensitivity tuning. Nonetheless, by manipulating the double acoustic vesicle in the rainforest cricket Paroecanthus podagrosus, selectively eliminating the sound-transmitting pathways, we revealed that these pathways contribute almost equally to the total amount of interaural intensity differences, emphasizing their functional relevance in the system.

10aacoustic communication10ainsect hearing10aInternally coupled ear10alaser Doppler vibrometry10aMatched filters10aSound localization1 aSchmidt, Arne, K. D.1 aRömer, Heiner uhttp://jeb.biologists.org/lookup/doi/10.1242/jeb.145524https://syndication.highwire.org/content/doi/10.1242/jeb.145524https://syndication.highwire.org/content/doi/10.1242/jeb.14552402433nas a2200193 4500008004100000245012400041210006900165300001400234490000800248520178300256653001502039653002402054653002902078653002302107653002502130100001902155700002402174856004102198 1986 eng d00aInsect hearing in the field II. Male spacing behaviour and correlated acoustic cues in the bushcricket Mygalopsis marki0 aInsect hearing in the field II Male spacing behaviour and correl a627–6380 v1593 a

1. Distances between calling maleMygalopsis marki Bailey (Orthoptera: Tettigoniidae) were measured in two geographically distinct populations. Mean intermale distances differed significantly in the two habitats (6.2 m and 11.5 m), but the sound pressure level of the nearest neighbour, measured at each focal male, was close to 65 dB SPL in both populations (Figs. 4, 6).

2. Using the response of an identified auditory interneuron as a ‘biological microphone’, the maximum hearing distance of males was tested. It was found to be affected by the size of the calling male, its posture, perch height and the vegetation density. Perch height alone influenced the maximum broadcast area of males by some 100%. Nearest neighbour distances were less than half the maximum hearing distances, confirming by neurophysiological methods that males do not space on threshold sensitivity to the complete call (Fig. 5).

3. The ability of the bushcricket to perceive the temporal characteristic of the call was also tested with the auditory interneuron over increasing distances from a signaller. The temporal integrity of the song was found to be maintained over the whole broadcasting area (Fig. 9).

4. The call has two energy peaks at 10 kHz and 20 kHz. The intensity of each peak attenuated differentially with increasing distance from the signaller; the low frequency component had a low variance at the nearest neighbour distance (SD: +4 dB/−6 dB) compared to the high frequency component (SD: +5 dB/−12.5 dB) (Fig. 8). The importance of the total sound pressure level and the relative intensity of the major frequency components of the song are discussed in relation to likely cues available to the male for maintaining spacing.

10aFocal Male10aFrequency Component10aHigh Frequency Component10aNeighbour Distance10aSound Pressure Level1 aRömer, Heiner1 aBailey, Winston, J. uhttps://bio.acousti.ca/es/node/5313501855nas a2200157 4500008004100000022001300041245008300054210006900137260001600206300001400222490000800236520135700244100002701601700001901628856005001647 1998 eng d a0028083600aEvolutionary transition from stretch to hearing organs in ancient grasshoppers0 aEvolutionary transition from stretch to hearing organs in ancien cAug-08-1999 a773 - 7760 v3943 a

Ears of modern insects occur on a wide variety of body parts and are thought to have evolved from ubiquitous stretch or vibration receptors1,2,3,4. This relationship, based on comparative anatomy and similarities in the embryological development of ears in divergent taxa5,6,7, has led to the widespread assumption of homology of these structures in insects, although this has not been tested rigorously. Here we report on the hearing organs of a relatively ancient8, atympanate bladder grasshopper9,10,11 (Bullacris membracioides), which is capable of signalling acoustically over ∼2 km12. We show that, within single individuals of this species, serially repeated abdominal ears show functional continuity from simple to more complex forms. All 12 morphologically differentiated organs respond to sound frequencies and intensities that are biologically significant, and mediate adaptive behavioural responses. By linking observations at the anatomical, physiological and behavioural level, our experiments provide evidence for the transition in function and selective advantage during the evolutionary development of this complex structure13,14. It is possible that ancestral insects with only simple pleural receptors had auditory capability covering distances substantially greater than contemporary insects with tympanate ears.

1 avan Staaden, Moira, J.1 aRömer, Heiner uhttp://www.nature.com/doifinder/10.1038/2951702432nas a2200241 4500008004100000022001400041245014400055210006900199260002000268300001600288490000800304520158900312653001801901653002501919653001201944653001201956653002201968653002301990100002002013700001902033700001802052856012002070 2013 eng d a0022-094900aMaintaining acoustic communication at a cocktail party: heterospecific masking noise improves signal detection through frequency separation0 aMaintaining acoustic communication at a cocktail party heterospe cOct-24-20132050 a4655 - 46650 v2163 a

We examined acoustic masking in a chirping katydid species of the Mecopoda elongata complex due to interference with a sympatric Mecopoda species where males produce continuous trills at high amplitudes. Frequency spectra of both calling songs range from 1 to 80 kHz; the chirper species has more energy in a narrow frequency band at 2 kHz and above 40 kHz. Behaviourally, chirper males successfully phase-locked their chirps to playbacks of conspecific chirps under masking conditions at signal-to- noise ratios (SNRs) of −8 dB. After the 2 kHz band in the chirp had been equalised to the level in the masking trill, the breakdown of phase-locked synchrony occurred at a SNR of +7 dB. The remarkable receiver performance is partially mirrored in the selective response of a first-order auditory interneuron (TN1) to conspecific chirps under these masking conditions. However, the selective response is only maintained for a stimulus including the 2 kHz component, although this frequency band has no influence on the unmasked TN1 response. Remarkably, the addition of masking noise at 65 dB sound pressure level (SPL) to threshold response levels of TN1 for pure tones of 2 kHz enhanced the sensitivity of the response by 10 dB. Thus, the spectral dissimilarity between masker and signal at a rather low frequency appears to be of crucial importance for the ability of the chirping species to communicate under strong masking by the trilling species. We discuss the possible properties underlying the cellular/synaptic mechanisms of the ‘novelty detector’.

10aambient noise10aauditory interneuron10ainsects10akatydid10anovelty detection10aselective encoding1 aSiegert, M., E.1 aRömer, Heiner1 aHartbauer, M. uhttp://jeb.biologists.org/cgi/doi/10.1242/jeb.089888https://syndication.highwire.org/content/doi/10.1242/jeb.08988802264nas a2200217 4500008004100000022001400041245009300055210006900148260001300217300001300230490000800243520163100251653002801882653001201910653001101922653001701933653000901950100002701959700001901986856004102005 1997 eng d a0022-094900aSexual signalling in bladder grasshoppers: tactical design for maximizing calling range.0 aSexual signalling in bladder grasshoppers tactical design for ma c1997 Oct a2597-6080 v2003 a

Pair formation in the bladder grasshopper (Bullacris membracioides) is by duetting and male phonotaxis. Low-frequency stridulatory signals are emitted by an abdominal resonator in the male and are answered by females using a species-specific time delay. Acoustic transmission in the natural environment was studied using playback of sexual signals over distances of 450m under two atmospheric conditions (day and night). Upward-refracting sound conditions and a sound shadow zone beyond approximately 50m prevailed during the day. Acoustic enhancement was demonstrated at night when downward-refracting temperature inversions created a tunnel effect with sound caught between the ground and zones of different temperatures. Transmission conditions are almost ideal at night when the species actually calls; calling distances of 150m for the male signal in the afternoon increased to 1.5-1.9km at night, arguably the largest calling distance yet reported for insects. In contrast, female calls transmit over a maximum of 50m, signifying a marked discrepancy in the active space of sex-specific signals. Transmission distance may, however, be profoundly affected by levels of masking noise. Adaptations to increase the signal range may variously be found in the signal itself, in behaviour patterns or in the sensory system. Here we demonstrate aspects of the first two types of adaptation in the sexual signalling system of a grasshopper in which maximizing the calling range appears to be the major selection pressure, with lesser effects imposed by inter- and intraspecific pressures and by the transmission channel.

10aanimal sexual behaviour10aAnimals10afemale10agrasshoppers10amale1 avan Staaden, Moira, J.1 aRömer, Heiner uhttps://bio.acousti.ca/es/node/20902