Academic literature on the topic 'Flight Phonotaxis'

In response to ultrasonic stimuli, tethered flying crickets perform evasive steering movements that are directed away from the sound source (negative phonotaxis). In this study we have investigated the responsiveness to ultrasound of neurons that descend from the cricket brain, and whether flight activity facilitates the responsiveness of these neurons. 1. Ultrasonic stimuli evoke descending activity in the cervical connectives both ipsilateral and contralateral to the sound source. 2. Both the amount of descending activity and the latency of this response in the cervical connectives are linearly correlated with ultrasonic stimulus intensity, regardless of the cricket's behavioral state. 3. Flight activity significantly increases the amount of descending activity evoked by ultrasound at all stimulus intensities, and significantly decreases the latency of the response in the cervical connectives compared with non-flying crickets. Flight activity, however, does not significantly affect the activity in an interneuron (Int-1) carrying ultrasound input to the brain. Thus, the increase in the amount of descending activity produced during flight activity is due to the integration of input from Int-1 and the flight motor system to ultrasound-sensitive neurons in the cricket brain. 4. Descending units recorded in the cervical connectives originate in the cricket brain. A reduction in the amount of descending activity is correlated with a decrease in the magnitude of the negative phonotactic response of the abdomen during flight activity, suggesting that these descending units play a role in eliciting negative phonotaxis.

Parameters of the calling song that were necessary to evoke phonotaxis in female bladder cicadas (Cystosoma saundersii) were determined for both longrange and short-range communication between the sexes. 1. Females flew to loudspeakers that were broadcasting model calling songs that resembled the natural calling song of the males. They also initiated courtship in response to the model calling songs. 2. When flying females were offered a choice between a model resembling the natural song in all parameters (the control model) and a model in which one of the temporal parameters had been changed (the experimental model), they were attracted equally to the control and experimental models. When the carrier frequency of the experimental model was changed, the females were attracted exclusively to the control model. 3. When the same model calling songs were presented to tethered, flying females in the laboratory, they turned only towards models with a carrier frequency close to that found in the natural song. Changing the temporal parameters of the model did not affect either the turning preferences of the females or their reaction times. 4. When the same series of control and experimental models were played, one at a time, to caged females in the laboratory, courtship responses were elicited only by models with temporal parameters similar to those of the natural song. In contrast, a wide range of carrier frequencies was found to elicit courtship, provided that the temporal parameters were similar to those of the control. 5. It is concluded that, in C. saundersii, identification of conspecific males by females is a two-stage process, with the carrier frequency of the male calling song being more important in long-range communication (flight) and the temporal parameters of the calling song being more important in short-range communication (courtship).

The acoustic startle/escape response is a phylogenetically widespread behavioral act, provoked by an intense, unexpected sound. At least six orders of insects have evolved tympanate ears that serve acoustic behavior that ranges from sexual communication to predator detection. Insects that fly at night are vulnerable to predation by insectivorous bats that detect and locate their prey by using biosonar signals. Of the six orders of insects that possess tympanate hearing organs, four contain species that fly at night and, in these, hearing is sensitive to a range of ultrasonic frequencies found in the biosonar signals of bats. Laboratory and field studies have shown that these insects (including some orthopterans, lepidopterans, neuropterans and dictyopterans), when engaged in flight behavior, respond to ultrasound by suddenly altering their flight, showing acoustic startle or negative phonotaxis, which serve as bat-avoidance behavior. A neural analysis of ultrasound-mediated escape behavior was undertaken in the field cricket Telegryllus oceanicus. An identified thoracic interneuron, int-1, was shown to trigger the escape response, but only when the cell was driven (synaptically or electrically) at high spike rates, and only when the insect was performing flight behavior; avoidance steering only occurs in the appropriate behavioral context: flight. Thus, significant constraints operate upon the ability of int-1 to trigger the escape response. The integration of auditory input and flight central pattern generator output occurs in the brain. It is found that neural activity descending from the brain in response to stimulation by ultrasound is increased when the insect is flying compared to when it is not. Although the behavioral act of avoidance steering may appear to be a simple reflex act, further analysis shows it to be anything but simple.

The responses of female Tettigonia viridissima to simulated bat echolocation calls were examined during tethered flight. The insects responded with three distinct behaviours, which occurred at graded stimulus intensities. At low intensities (threshold 54 dB SPL), T. viridissima responded by steering away from the sound source (negative phonotaxis). At intensities approximately 10 dB higher, beating of the hindwing was interrupted, although the insect remained in the flight posture. A diving response (cessation of the wingbeat, closure of the forewings and alignment of the legs against the body) occurred with a threshold of 76 dB SPL. Considering these thresholds, we estimate that the diving response occurs at approximately the sound amplitude at which many aerial-hawking bats first receive echoes from the insect. The other behaviours probably occur before the bat detects the insect and should therefore be interpreted as early avoidance behaviours. The repertoire of startle responses in T. viridissima, with directional and non-directional components, is similar to those of crickets and moths, but quite different from those described for another bushcricket (Neoconocephalus ensiger), which shows only a non-directional response. This supports the conclusion that bat-evasive behaviours are not conserved within the Tettigoniidae, but instead are shaped by the ecological constraints of the insects.

Flying locusts orient to sounds in their environment. Sounds similar to those produced by echolocating bats cause a flying locust to change its flight path. We used high-speed cinematography and videography to study changes in body posture and wing kinematics of tethered locusts in response to stimulation with bat-like sounds. Locusts showed both negative and positive phonotaxis to this stimulus. Within a few wingbeats of stimulus onset (between 126 and 226ms), locusts deflected their abdomens to one side, and the angle of the left and right forewings with respect to the dorsal­ventral body axis became asymmetrical during the downstroke. This forewing asymmetry, in which the forewing on the inside of the turn became more depressed, ranged from 20 to 45° (37±9.7°, mean ± s.d.) and was correlated with the direction and magnitude of abdomen deflection, a measure of steering in tethered, flying locusts. Hindwing stroke angle asymmetries were minimal or non-existent after stimulation. Coincident with changes in forewing asymmetry and abdomen deflection was a decrease in stroke amplitude (19±6.5°) of the forewing on the inside of the attempted turn. Motor patterns from forewing first basalar (M97) muscles showed an asymmetry in the timing of left and right depressor activation that ranged from 10.4 to 1.6ms (4.23±2.85ms). The number of spikes per depressor burst increased to a maximum of three spikes in the muscle on the inside of the attempted turn, and depressor frequency (wingbeat frequency) increased by approximately 2Hz (2.17±0.26Hz). We suggest that the asymmetry in forewing first basalar activity is causally related to the asymmetry in the timing of the initiation of the downstroke, resulting in an asymmetry in the ranges of the stroke angles of the forewings, which would impart a roll torque to the locust. This would augment the steering torques generated by concurrent changes in the angle of attack of the fore- and hindwings and changes in abdomen position to effect rapid avoidance manoeuvres.

Abstract Background Release of gene-drive mutants to suppress Anopheles mosquito reproduction is a promising method of malaria control. However, many scientific, regulatory and ethical questions remain before transgenic mosquitoes can be utilised in the field. At a behavioural level, gene-drive carrying mutants should be at least as sexually attractive as the wildtype populations they compete against, with a key element of Anopheles copulation being acoustic courtship. We analysed sound emissions and acoustic preference in a doublesex mutant previously used to collapse Anopheles gambiae (s.l.) cages. Methods Anopheles rely on flight tones produced by the beating of their wings for acoustic mating communication. We assessed the impact of disrupting a female-specific isoform of the doublesex gene (dsxF) on the wing beat frequency (WBF; measured as flight tone) of males (XY) and females (XX) in homozygous dsxF− mutants (dsxF−/−), heterozygous dsxF− carriers (dsxF+/−) and G3 dsxF+ controls (dsxF+/+). To exclude non-genetic influences, we controlled for temperature and wing length. We used a phonotaxis assay to test the acoustic preferences of mutant and control mosquitoes. Results A previous study showed an altered phenotype only for dsxF−/− females, who appear intersex, suggesting that the female-specific dsxF allele is haplosufficient. We identified significant, dose-dependent increases in the WBF of both dsxF−/− and dsxF+/− females compared to dsxF+/+ females. All female WBFs remained significantly lower than male equivalents, though. Males showed stronger phonotactic responses to the WBFs of control dsxF+/+ females than to those of dsxF+/− and dsxF−/− females. We found no evidence of phonotaxis in any female genotype. No male genotypes displayed any deviations from controls. Conclusions A prerequisite for anopheline copulation is the phonotactic attraction of males towards female flight tones within mating swarms. Reductions in mutant acoustic attractiveness diminish their mating efficiency and thus the efficacy of population control efforts. Caged population assessments may not successfully reproduce natural mating scenarios. We propose to amend existing testing protocols to better reflect competition between mutants and target populations. Our findings confirm that dsxF disruption has no effect on males; for some phenotypic traits, such as female WBFs, the effects of dsxF appear dose-dependent rather than haplosufficient.

The spectacular diversity in the pair-formation strategies among animal groups has attracted the attention of many over the years. The roots of this diversity lie in the diversity of challenges that males and females face in finding a potential mate. Successful localisation of mates requires effective information flow between the sexes regarding location, availability and, in some cases, quality. To this end, animals have evolved different kinds of signals, signalling and search strategies to counter the various challenges and facilitate encounter. A major factor affecting the information flow between the sexes is the spatio-temporal distribution of the sexes, as signals and sensory physiologies are constrained spatio-temporally. The spatio-temporal distribution of males and females is in turn a function of two major factors: resource distribution and parental investment of the sexes. Depending on whether the resource distribution is patchy or uniform, individuals can be clumped in space or evenly dispersed, influencing their pair-formation strategies. Parental investment can further alter the relative distribution of males and females by affecting the time that males and females can be sexually receptive. Higher parental investment of a particular sex can lead to these individuals being out of the mating pool longer, causing a bias in the ratio of sexually receptive males to females (Operational Sex Ratio) at any given point in time, consequently impacting pair-formation strategies. Orthopterans are well known models for studies on acoustic communication owing to the diversity in signals and pair-formation strategies. Conventionally, males function as the static signalling sex and use long-range acoustic signals to direct the phonotactic response of silent females. There are deviations observed, with females responding to calling males via acoustic signals, with males (or both males and females) performing localisation. Onomarchus uninotatus, a canopy inhabiting paleotropical false-leaf katydid, presents a unique departure, wherein the two sexes employ signals that function at different spatial scales. Males broadcast long- range acoustic signals and the females respond via vibratory signals that are then used by males to localise females. Laboratory experiments have established vibratory signals to be an immediate response to male calls even at the threshold of female hearing. Being a canopy species, relying on short-range vibratory signals for localisation across trees and at larger distances appears paradoxical. In my thesis, I therefore investigated the localisation strategies of Onomarchus uninotatus across two spatial scales, i.e. within and between trees, and aimed to understand if the roles played by the sexes are reflected in their relative parental investment. For the across-tree scale, I studied the spatial structure of calling males and their preferred calling sites (Artocarpus spp.) in their natural habitat. Using the information on male spacing, call transmission and hearing thresholds, I computed the perceptual spaces of male signals to understand the acoustic environment of calling males and females. It was found that both calling males and females could hear calls of males from neighbouring trees with a probability of 0.76 and 0.59 respectively. Although males were found to be dispersed, significant overlap was seen in their acoustic ranges. I then investigated female flight responses to male acoustic signals in laboratory experiments, wherein male acoustic signals were played back from loudspeakers that were not connected to the substrate on which the females were placed. Females typically tremulated first, followed sometimes by initiation of flight, suggesting that females may perform flight phonotaxis to locate calling males on a different tree. Using the information gathered from these studies, I then used a simulation framework to elucidate optimal mate encounter strategies at the across-tree spatial scale. The across-tree spatial distribution of the sexes was varied in the simulations and the encounter efficiencies quantified for different movement patterns of both males and females, using the data on spatio- acoustic patterning of callers in this system. Stationary calling males with localising females was found to be the optimal strategy across all spatial distributions. To understand pair-formation strategies at the within-tree spatial scale, field experiments were conducted in a semi-natural setup to observe interactions between a calling male and a responsive female at two different distances on a branch. Interestingly, females always tremulated first, irrespective of their distance from the caller. At larger distances, some females were found to perform phonotaxis, but only after a bout of tremulation. Finally, I examined the relative parental investment of the sexes using re-signalling intervals as a proxy. Given that both males and females invest in localisation, parental investments of the sexes were predicted to be comparable. Preliminary results from re-signalling intervals indicate that the sexes have comparable parental investment in this species.