1. Acoustically guided movement in a three‐dimensional space is a complex behavioural task performed notably by birds, bats, and some insect species. The precision of acoustic orientation depends on ...the directionality of the hearing system as well as on auditory behaviour. 2. The fly Emblemasoma auditrix Diptera (Sarcophagidae) is a parasitoid of the cicada Okanagana rimosa Auchenorrhyncha (Cicadidae) and locates its host in the complex habitat of a forest. The phonotactic behaviour of the fly was analysed experimentally with emphasis on the vertical domain in the field. Different experimental setups allowed discriminating subsequent steps in the phonotactic behaviour of E. auditrix. 3. During the phonotactic flight, flies first landed on landmarks, which were used to re‐adjust to the elevation of the sound source. Acoustic targets were located from these resting positions. The sound source elevation was detected at the start of the flight as the longitudinal body axis was adjusted to the inclination of the target sound source. 4. Flies usually did not land directly upon the sound source, but landed nearby, and most often above the target. Within the target area, types of movement for the final approach differed in respect to target position; flies walked predominantly if the final target was located above or below, but for horizontally located targets much of the distance was covered by flight. 5. In conclusion, E. auditrix can locate the acoustic target in complex habitats and uses a flexible multi‐step approach for short‐range phonotaxis.
Detection of substrate vibrations is an evolutionarily old sensory modality and is important for predator detection as well as for intraspecific communication. In insects, substrate vibrations are ...detected mainly by scolopidial (chordotonal) sense organs found at different sites in the legs. Among these sense organs, the tibial subgenual organ (SGO) is one of the most sensitive sensors. The neuroanatomy and physiology of vibratory sense organs of cicadas is not well known. Here, we investigated the leg nerve by neuronal tracing and summed nerve recordings. Tracing with Neurobiotin revealed that the cicada Okanagana rimosa (Say) (Hemiptera: Cicadidae) has a femoral chordotonal organ with about 20 sensory cells and a tibial SGO with two sensory cells. Recordings from the leg nerve show that the vibrational response is broadly tuned with a threshold of about 1 m/s2 and a minimum latency of about 6 ms. The vibratory sense of cicadas might be used in predator avoidance and intraspecific communication, although no tuning to the peak frequency of the calling song (9 kHz) could be found.
Safflower (Carthamus tinctorius L.) serves as a reference dicot for investigation of defence mechanisms in Asteraceae due to abundant secondary metabolites and high resistance/tolerance to ...environmental stresses. In plants, phenylpropanoid and flavonoid pathways are considered as two central defence signalling cascades in stress conditions. Here, we describe the isolation of two major genes in these pathways, CtPAL (phenylalanine ammonia-lyase) and CtCHS (chalcone synthase) in safflower along with monitoring their expression profiles in different stress circumstances. The aa (amino acid) sequence of isolated region of CtPAL possesses the maximum identity up to 96% to its orthologue in Cynara scolymus, while that of CtCHS retains the highest identity to its orthologue in Callistephus chinensis up to 96%. Experiments for gene expression profiling of CtPAL and CtCHS were performed after the treatment of seedlings with 0.1 and 1 mM SA (salicylic acid), wounding and salinity stress. The results of semi-quantitative RT-PCR revealed that both CtPAL and CtCHS genes are further responsive to higher concentration of SA with dissimilar patterns. Regarding wounding stress, CtPAL gets slightly induced upon injury at 3 hat (hours after treatment) (hat), whereas CtCHS gets greatly induced at 3 hat and levels off gradually afterward. Upon salinity stress, CtPAL displays a similar expression pattern by getting slightly induced at 3 hat, but CtCHS exhibits a biphasic expression profile with two prominent peaks at 3 and 24 hat. These results substantiate the involvement of phenylpropanoid and particularly flavonoid pathways in safflower during wounding and especially salinity stress.
A primary task of auditory systems is the localization of sound sources in space. Sound source localization in azimuth is usually based on temporal or intensity differences of sounds between the ...bilaterally arranged ears. In mammals, localization in elevation is possible by transfer functions at the ear, especially the pinnae. Although insects are able to locate sound sources, little attention is given to the mechanisms of acoustic orientation to elevated positions. Here we comparatively analyse the peripheral hearing thresholds of three species of bushcrickets in respect to sound source positions in space. The hearing thresholds across frequencies depend on the location of a sound source in the three-dimensional hearing space in front of the animal. Thresholds differ for different azimuthal positions and for different positions in elevation. This position-dependent frequency tuning is species specific. Largest differences in thresholds between positions are found in Ancylecha fenestrata. Correspondingly, A. fenestrata has a rather complex ear morphology including cuticular folds covering the anterior tympanal membrane. The position-dependent tuning might contribute to sound source localization in the habitats. Acoustic orientation might be a selective factor for the evolution of morphological structures at the bushcricket ear and, speculatively, even for frequency fractioning in the ear.
The auditory networks of Orthoptera offer a model system uniquely suited to the study of neuronal connectivity and lesion-dependent neural plasticity. Monaural animals, following the permanent ...removal of one ear in nymphs or adults, adjust their auditory pathways by collateral sprouting of afferents and deafferented interneurons which connect to neurons on the contralateral side. Transient lesion of the auditory nerve allows us to study regeneration as well as plasticity processes. After crushing the peripheral auditory nerve, the lesioned afferents regrow and re-establish new synaptic connections which are relevant for auditory behavior. During this process collateral sprouting occurs in the central nervous networks, too. Interestingly, after regeneration a changed neuronal network will be maintained. These paradigms are now been used to analyze molecular mechanism in neuronal plasticity on the level of single neurons and small networks.
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