Selective phonotaxis in <Emphasis Type="Italic">Neoconocephalus nebrascensis</Emphasis> (Orthoptera: Tettigoniidae): call recognition at two temporal scales

The calls of many Orthopteran species are comprised of a simple trill of pulses, the temporal pattern of which is important for call recognition. Male Neoconocephalus nebrascensis produce pulses with a temporal structure typical for the genus. However, they modify this pattern by grouping their pulses into verses, thereby creating a higher order temporal structure. The importance of the pulse pattern and verse structure for call recognition in N. nebrascensis was determined using a walking compensator. Females required the conspecific pulse pattern for call recognition, responding only when the intervals between pulses were short or absent. Females also required the verse structure for call recognition, and recognized the verse structure only when the amplitude modulation depth between verses and pauses exceeded 18 dB. We discuss that the verse recognition mechanism is a derived trait adapted for pre-mating isolation. We hypothesize that the unusually large amplitude modulation required for verse recognition forces males to synchronize their calls in order to preserve an attractive pattern. Call synchrony appears to be the outcome of cooperation, rather than competition, in this species.     

Phonotaxis and aggression in the coneheaded katydid Neoconocephalus affinis

ABSTRACT. Positive phonotaxis to tape recorded conspecific song by males of the katydid Neoconocephalus affinis (Beauvois) (Orthoptera: Tettigoniidae) was studied in the field, in Puerto Rico. N.affinis males stridulated loudly during evening hours, and most males were territorial. Aggression between neighbours occurred, albeit rarely, and playback experiments using tape recordings of N.affinis song showed that aggressive behaviour, in the form of jumps directed toward a loudspeaker, could be elicited from a male by song broadcast above a threshold sound intensity. Response thresholds for different males varied from 76 to 93 dB, intensities that corresponded to calculated inter-neighbour distances of 1.6-0.26 m, respectively. Insects that had lower response thresholds were on average more isolated from neighbours and also stridulated more persistently and at a higher sound intensity than insects with higher response thresholds. N.affinis males displayed no phonotaxis toward the song of Neoconocephalus maxillosus , a sympatric species whose song is similar to that of N.affinis in principal frequency but differs in wingstroke rate. Phonotaxis toward conspecific song could only be elicited from males while they were silent.     

Phonotactic response of female crickets on the Kramer treadmill: methodology, sensory and behavioural implications

Since population-level variation in female mating preferences can shape intraspecific communication systems within the context of sexual selection it is essential to quantify these preferences and their sources of variation. We calculated individual female response functions for four male calling song traits in the field cricket Gryllus bimaculatus, by performing untethered phonotaxis measurements on a spherical locomotor compensator (Kramer treadmill). Firstly, we quantify the population-level sources of phonotactic variation and correct for factors that adversely affect this measurement. Secondly, we develop methodology for the characterisation of individual female phonotactic response functions suitable for population-level analyses and demonstrate the applicability of our method with respect to recent literature on Orthopteran acoustic communication. Phonotaxis towards a preferred stimulus on different occasions is highly repeatable, with lower repeatabilities away from the most preferred signal traits. For certain male signal traits, female preference and selectivity are highly repeatable. Although phonotactic response magnitude deteriorated with age, preference functions of females remained the same during their lifetimes. Finally, the limitations of measuring phonotaxis using a spherical locomotor compensator are described and discussed with respect to the estimation of the selectivity of female response.     

Persistence of phonotaxis in females of four species of crickets following allatectomy

The role of Juvenile Hormone III in phonotaxis, mating behavior and egg production of cricket females from Gryllus campestris, Gryllus bimaculatus, Teleogryllus commodus, and Acheta domesticus was investigated.

Behavioural patterns, preference, and motivation of female midwife toads during phonotaxis tests

During two-speaker phonotaxis tests performed with female midwife toads (Alytes obstetricans and A. cisternasii), the occurrence of behavioural patterns tentatively considered to be associated with entering amplexus and making a mate choice was noted. The individual repeatability of choice was assessed as a measurement of reliability of female preference, and the individual repeatability of response was assessed as a measurement of the degree of female motivation. The tests were grouped in two categories, spectral and temporal, according to the acoustic variable addressed in the test. Females selecting the alternative chosen less often by the population responded less often in phonotaxis tests and thus could be less motivated. Female repeatability was significant for temporal tests, but not for spectral tests. The observation of behavioural patterns during phonotaxis tests appears to be a useful complement to mate choice studies in anurans. Electronic Publication     

Directional hearing in the gray tree frog Hyla versicolor: Eardrum vibrations and phonotaxis

1. We used laser vibrometry to study the vibrational frequency response of the eardrum of female gray tree frogs for different positions of the sound source in three-dimensional space. Furthermore, we studied the accuracy of 3-D phonotaxis in the same species for sounds with different frequency contents. 2. The directionality of the eardrum was most pronounced in a narrow frequency range between 1.3 and 1.8 kHz. 3. The average 3-D, horizontal and vertical jump error angles for phonotactic approaches with a sound similar to the natural advertisement call (1.1 and 2.2 kHz frequency components) were 23 degrees, 19 degrees and 12 degrees, respectively. 4. 3-D jump error angle distributions for the 1.4 + 2.2 kHz, 1.0 kHz and 2.0 kHz sounds were not significantly different from that for the 1.1 + 2.2 kHz sound. 5. The average 3-D jump error angle for the 1.4 kHz sound was 36 degrees, and the distribution was significantly different from that for the 1.1 + 2.2 kHz sound. Hence, phonotactic accuracy was poorer in the frequency range of maximum eardrum directionality. 6. Head scanning was not observed and is apparently unnecessary for accurate sound localization in three-dimensional space. 7. Changes in overall sound pressure level experienced by the frog during phonotactic approaches are not an important cue for sound localization.     

Developmental control of ultrasound sensitivity by a juvenile hormone analog in crickets (Teleogryllus oceanicus)

Cricket ears are sensitive to ultrasound as well as to lower, cricket-like sound frequencies. Ultrasound stimuli evoke negative phonotaxis in flying crickets, a behavior that has been interpreted as a defensive response against predation by echolocating bats. A recent study on a wing-dimorphic species, Gryllus texensis, showed that short-winged individuals, which are incapable of flight, are less sensitive to ultrasound, but not to lower sound frequencies, than their long-winged counterparts. The developmental decision to develop as a long- or short-winged individual is made during the last two larval instars, and there is some evidence suggesting that juvenile hormone (JH) has an instructive role, such that high levels of JH result in short-winged individuals. We show that treatment of last-instar larvae of a monomorphic long-winged species, Teleogryllus oceanicus, with a JH analog causes a decrease in sensitivity to ultrasound, but not to the lower sound frequency used for intraspecific communication.     

Auditory-evoked evasive manoeuvres in free-flying locusts and moths

We presented free-flying locusts (Locusta migratoria L.) with sounds that varied in temporal structure and carrier frequency as they flew toward a light source in a flight room under controlled temperature and light conditions. Previous studies have shown tethered locusts react more often to trains of 30-kHz pulses than to pulse trains below 10 kHz. Further, this acoustic startle response has been suggested to function in bat-avoidance. We expected free-flying locusts to respond similarly; however, we found locusts responded to all sounds we presented, not just high-frequency, bat-like sounds. Response rates of turns, loops, and dives varied from 6% to 26% but were statistically independent of carrier frequency and/or pulse structure. Free-flying moths and tethered locusts were tested using a subset of our acoustic stimuli under the same temperature and light conditions as the free-flying locusts. Moth responses were carrier frequency dependent as were responses of tethered locusts positioned along the flight path observed in our free-flight trials. All responses were unaffected by a 90% reduction in room light. We conclude that locusts possess an acoustic startle response evocable in free flight, however, free-flying locusts do not show the same discrimination observed in tethered locusts under similar conditions.Abbreviations ASR acoustic startle response - dB SPL decibel sound pressure level (RMS re: 20 Pa)     

Temporal and directional processing by an identified interneuron,ON1, compared in cricket species that sing with different tempos

We compare the temporal and directional processing properties of an identified auditory interneuron, ON1, between species with calling songs containing relatively low and high pulse rates (Teleogryllus oceanicus and Gryllus texensis, respectively). Using information theory, we find that the ON1 of G. texensis encodes higher amplitude-modulation frequencies than that of T. oceanicus. Bilateral differences in ON1 responses are also more pronounced in G. texensis, particularly for rapid, G. texensis-like stimuli. We show that brief silent intervals in a pulse train, such as those that occur in the natural calling song of G. texensis, enhance the representation of the stimulus pulse pattern as well as bilateral differences in activity. Our results suggest that the characteristics of an identified neuron vary, across cricket species, in accordance with the temporal structures of their communication signals.