Can spectral cues contribute to species separation in closely related grasshoppers?

 The acridid grasshoppers Chorthippus biguttulus and Ch. mollis, which are closely related and often sympatric species, were compared intra- and interspecifically with regard to the spectra of their calling and courtship songs and of the sound-induced vibrations of the tympanal membrane, as well as the threshold curves of the tympanal nerve. In the low-frequency range but not in the ultrasound region, the maxima of these various curves fall at distinctly different frequencies in the two species. It is shown that the low-frequency sensitivity of the auditory system in both species, especially in females, is well matched to the conspecific song spectra but not to those of the heterospecific songs. Whether these characteristics actually contribute to species discrimination remains to be determined by behavioural tests. Accepted: 23 August 1996     

Neuropharmacological evidence for inhibitory cephalic control mechanisms of stridulatory behaviour in grasshoppers

In gomphocerine grasshoppers the neuromuscular patterns of stridulatory hindleg movements are produced by metathoracic rhythm generators under the control of cephalic command neurons. Injections of cholinergic agonists into the protocerebrum activate this command system which induces the performance of stridulatory sequences, resembling natural species specific movements. Injections of GABA, glycine and picrotoxin into the central protocerebrum of the species Omocestus viridulus, Chorthippus mollis and Ch. biguttulus revealed a contribution of inhibitory mechanisms to the control of the stridulatory behaviour. The experiments suggest that inhibition interferes with the cephalic command systems at three levels: (1) sustained inhibition through picrotoxin sensitive receptors acting on all command units while grasshoppers are at rest, and during stridulation on all command units except the one activating the pattern generators of the currently performed movements; (2) premature termination of song sequences, experimentally induced by injections of GABA and glycine; and (3) coupling of a timing mechanism that terminates a song sequence or its subunits with a particular movement pattern after specific durations. These results together with those from previous studies on the pharmacological activation of stridulatory behaviour suggest that a balance of inhibitory and excitatory inputs to the command system selects the appropriate song type and controls its performance. Accepted: 11 June 1998     

Descending stridulatory interneurons in the suboesophageal ganglion of two grasshopper species

1. The activity of interneurons in the suboesophageal ganglion of the acridid grasshoppers Omocestus viridulus (L.) and Chorthippus mollis (Charp.), recorded intracellularly during stridulation, was found to conform to the rhythm of the singing movements. The arborizations of these neurons in this ganglion are largely bilaterally symmetrical; the axon descends contralaterally to the soma and passes at least into the metathoracic ganglion.
2. The anatomical and physiological characteristics of these neurons are similar in the two species and of four types. Three of them exhibit a tonic, spontaneous activity in the resting animal, which is modulated in the stridulatory rhythm as soon as singing begins. The fourth type has no resting activity and discharges only during the song, in a stridulation-specific pattern.
3. By transecting the connectives it was shown that the rhythmic activity of the neurons is not determined by input from the brain, nor is it generated in the suboesophageal ganglion itself. It is based on information about the song pattern that ascends from the thoracic ganglia.

     

Serotonin in the leech central nervous system: anatomical correlates and behavioral effects

Summary Stridulation of grasshoppers is controlled by hemisegmental pattern generator subunits which probably are restricted to the metathoracic ganglion complex (TG3-complex). The coordination of left and right pattern generator subunits depends on commissures of the TG3-complex (Ronacher 1989). The coordination of the stridulatory movements was studied in Chorthippus dorsatus males with partial mediosagittal incisions in the TG3-complex.Animals bearing anterior incisions in the TG3-complex, by which all commissures of the metathoracic neuromere and the first abdominal neuromere were transected, were still able to produce bilaterally coordinated species-specific stridulatory movements. Commissures of the T3- and A1-neuromere, thus, are not necessary, and the A2-, A3-commissures are sufficient for this coordination (Figs. 3, 4).Animals with partial posterior incisions, extending until A1, had deficits in their stridulation pattern; the coordination between the hindlegs was impaired though not completely lost (Fig. 6). This is discussed in view of the structure of stridulation interneurons identified in a related grasshopper species (Omocestus viridulus).These results indicate an unexpected substantial contribution of the abdominal neuromeres A2 and A3 to the control of stridulatory movements. This constitutes an interesting parallel to the flight control system of locusts where interneurons located in the first 3 abdominal neuromeres also appear to contribute to the flight pattern generator (Robertson et al. 1982).Abbreviations A1–A3 abdominal neuromeres 1–3 - T3 metathoracic neuromere - TG3-complex metathoracic ganglion complex including A1–A3     

Separate localization of sound recognizing and sound producing neural mechanisms in a grasshopper

Summary In the two acridid speciesChorthippus parallelus andCh. montanus, the sound template by which females recognize male song varies with temperature, as does the song itself. At relatively high temperatures the females respond best to simulated songs with high syllable frequencies, and at lower temperatures songs with lower syllable frequencies are preferred.The temperature around the supraesophageal and metathoracic ganglia of female grasshoppers was monitored by implanted thermocouples, and either the head or the thorax was warmed selectively while the animal was free to move (within the imits of the wires). Then simulations of the conspecific song varying in syllable frequency corresponding to different song temperatures were presented, and the stridulatory responses of the animals were observed.The results were as follows. 1. Song recognition (in particular, the position of the peak of the response curve) depended on the temperature of the head. 2. The rate of stridulatory hindleg movement was determined by the temperature of the thoracic ganglia.This result provides strong evidence against the genetic coupling hypothesis.     

Pharmacological Activation of Stridulation in the Grasshopper Chorthippus albomarginatus (Orthoptera: Gomphocerinae)

Calling and courtship stridulatory behavior of Chorthippus albomarginatus was induced by injections of acetylcholine agonists into the protocerebrum. Pharmacologically induced stridulation, in many parameters, was quite similar to the natural behavior. However, the order of the courtship element alternation was different from that of the natural song. In some cases the pharmacologically induced stridulation included only one or two courtship elements. Based on the exclusive stimulation of a particular element of courtship songs and similarity of its movement pattern with the calling song, both patterns of Ch. albomarginatus stridulation appear to be homologous. The results obtained on this species confirm the idea of a hierarchic organization of the central nervous control of stridulation in gomphocerine grasshoppers and indicate participation of certain protocerebrum structures in this control.     

Stridulation of acridid grasshoppers after hemisection of thoracic ganglia: evidence for hemiganglionic oscillators

In the grasshopperChorthippus biguttulus the stridulatory movements of males with surgically manipulated ventral nerve cords were investigated.

On the control of stridulation in the acridid grasshopper Omocestus viridulus L.

Summary In tethered, minimally dissected grasshoppers stridulation was elicited by DC brain stimulation. Intracellular recording, stimulation and staining of interneurons in the metathoracic ganglion complex were performed simultaneously with measurements of hindleg movements. The functional significance of interneurons for generation of the stridulation rhythm and bilateral coordination of the hindlegs was tested and quantitatively analysed. Interneurons involved in stridulation were found in the metathoracic and abdominal neuromeres. Typically they included arborizations in a dorsal neuropil parallel to the long axis of the ganglion. Interneuron T3-LI-3 started and drove the ipsilateral rhythm generator. The stridulation rhythm was reset by interneuron A1-AC-1. It was stopped if interneuron T3-AC-1 was stimulated. Bilateral coordination of stridulation movements was based on excitatory and inhibitory pathways between the hemiganglionic networks. Switching in the coordination of hindleg movement patterns was induced by changes in the discharge rate of the bilateral arborizing interneuron T3-LC-4. The hemiganglionic interneurons T3-LI-3 and T3-LI-1 influenced coordination via the activity level within the networks.     

‘Switching-off’ of an auditory interneuron during stridulation in the acridid grasshopperChorthippus biguttulus L.

Summary In freely moving grasshoppers of the speciesChorthippus biguttulus compound potentials were recorded from the neck connectives with chronically implanted hook electrodes. The spikes of one large auditory interneuron, known as the G-neuron (Kalmring 1975a, b) were clearly distinguishable in the recordings and the neuron was identified by its physiology and morphology. In quiescent grasshoppers the G-neuron responds to auditory and vibratory stimuli, but responses to both stimuli are suppressed during stridulation in males (Fig. 1, top, Fig. 7). When a male's wings were removed so that the stridulatory movements of its hindlegs produced no sound, the suppression of the G-neuron response still occurred (Fig. 1, bottom). When proprioceptive feedback from the hindlegs was reduced, by forced autotomy of the legs, the switching-off remained incomplete (Fig. 3) (production of stridulatory patterns was inferred on the basis of electromyograms from the relevant thoracic musculature). Imposed movement of the hindlegs, on the other hand, suppressed the G-neuron response in a graded fashion, depending on the frequency of the movement (Figs. 4 and 5). These experiments suggest that the switching-off is brought about by a combination of proprioceptive feedback and central efferences. The switching-off phenomenon could either protect the grasshopper's auditory pathway from undesired effects of overloading by its own intense song (e.g. self-induced habituation as described by Krasne and Wine 1977) and should therefore apply for most auditory neurons. Alternatively it could prevent escape reflexes from being triggered by stridulatory self-stimulation and consequently might apply only for neurons involved in such networks (as the G-neuron might be).     

Variation in complex courtship traits across a hybrid zone between grasshopper species of the Chorthippus albomarginatus group

Closely related grasshopper species of the Chorthippus albomarginatus group are notable for their extremely complex courtship songs, accompanied by a visual display. Two species of this group, Ch. albomarginatus and Ch. oschei, were previously shown to hybridize in a wide mosaic hybrid zone in Ukraine and Moldova. In this paper, variation in five courtship song characters, one character of visual display and the number of stridulatory pegs were analysed across the hybrid zone to estimate selection against hybrids and strength of assortative mating. Comparison of cline width and position across the hybrid zone showed concordant and coincident clines in four traits, such as three song characters and one morphological character, and discordant and non‐coincident clines in two other song characters and the character of visual display. Concordance of clines in different characters suggests an equal strength of selection acting on underlying loci. Increase of variance and covariance between phenotypic traits at the cline centre could more likely result from assortative mating than from selection against hybrids. Most pairwise cases showed the highest covariance for the oschei‐like, than for the albomarginatus‐like hybrid populations. This indicates that introgression of the oschei genes into the albomarginatus genome is stronger than vice versa, and may be evidence of the movement of the hybrid zone in favour of Ch. albomarginatus. Analysis of associations between phenotype and local vegetation showed that mosaic structure of the hybrid zone is explained to a great extent by habitat–phenotype associations. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 275–291.     

Regeneration of axotomized tympanal nerve fibres in the adult grasshopper Chorthippus biguttulus (L.) (Orthoptera: Acrididae) correlates with regaining the localization ability

Adult males of the grasshopper Chorthippus biguttulus exhibit a stereotyped turning behaviour towards the direction of the female song. This behaviour has been used to study the regeneration of synaptic connections used for pattern recognition and sound localization. Unilaterally deafened animals are not able to localize the sound direction and turn exclusively towards the intact side, regardless of the speaker position. This behaviour does not change with postoperative time. After an axotomy of the tympanic nerve fibres the sensory axons regrow and regenerate their synaptic contacts which is deduced from the recovery of the ability to localize sound. The behavioural threshold for stimulation from the operated side is increased by approx. 5 dB SPL. The probability of correct turning towards the operated side increases with postoperative time. The ability for lateralization improves with postoperative time and may reach values of intact animals (discrimination of 1–2 dB SPL difference. Animals with two operations (axotomy of one tympanal nerve and blocking of the other ear) do not react to the female song, which suggests that recognition of the species-specific song pattern is not possible with the regenerated fibres and their synaptic connections alone. Neuroanatomical studies show that the regeneration of localization ability is correlated with an ingrowth of sensory fibres into the frontal auditory neuropil of the metathoracic ganglion.     

Recognition of a two-element song in the grasshopper Chorthippus dorsatus (Orthoptera: Gomphocerinae)

Summary Males of the grasshopper Chorthippus dorsatus produce songphrases which contain two differently structured elements — pulsed syllables in the first part (A) and ongoing noise in the second part (B). Females of Ch. dorsatus answer to artificial song models only if both elements A and B are present. Females strongly prefer song models in which the order of elements is A preceding B. Females discriminate between the two elements mainly by the existence of gaps within A-syllables. Pulses of 5–8 ms separated by gaps of 8–15 ms make most effective A-syllables, while syllable duration and syllable intervals are less critical parameters. Females respond to models which contain more than 3 A-syllables with high probability. Female model preferences lie well in the range of parameter values produced by singing males, except for B-parts which must be longer than those of any natural song to be most effective. In ancestors of Ch. dorsatus the two elements of the songs might have been directed towards females (part A) and males (part B).     

A population genomic scan in Chorthippus grasshoppers unveils previously unknown phenotypic divergence

Understanding the genetics of speciation and the processes that drive it is a central goal of evolutionary biology. Grasshoppers of the Chorthippus species group differ strongly in calling song (and corresponding female preferences) but are exceedingly similar in other characteristics such as morphology. Here, we performed a population genomic scan on three Chorthippus species (Chorthippus biguttulus, C. mollis and C. brunneus) to gain insight into the genes and processes involved in divergence and speciation in this group. Using an RNA‐seq approach, we examined functional variation between the species by calling SNPs for each of the three species pairs and using F_ST‐based approaches to identify outliers. We found approximately 1% of SNPs in each comparison to be outliers. Between 37% and 40% of these outliers were nonsynonymous SNPs (as opposed to a global level of 17%) indicating that we recovered loci under selection. Among the outliers were several genes that may be involved in song production and hearing as well as genes involved in other traits such as food preferences and metabolism. Differences in food preferences between species were confirmed with a behavioural experiment. This indicates that multiple phenotypic differences implicating multiple evolutionary processes (sexual selection and natural selection) are present between the species.     

The effects of injecting Juvenile Hormone III into the prothoracic ganglion on phonotaxis by female crickets Gryllus bimaculatus

Nanoinjection of Juvenile Hormone III (JH III) into the prothoracic ganglion causes virgin female crickets Gryllus bimaculatus De Geer to become more phonotactically selective for the syllable periods (SPs) of model calling songs. Females responding to all, or almost all, of the SPs presented before JH III injection significantly narrow their responses to a range of SPs that is usually centered on the SPs included in the conspecific males' calling song. Control injections of acetone (i.e. the solvent for JH III) into the prothoracic ganglion do not significantly change the recipient females' phonotactic responses. Injection of JH III into the metathoracic ganglion also has no effect the females' phonotactic choices.     

ACOUSTIC COMMUNICATION DISTANCES OF A GOMPHOCERINE GRASSHOPPER

ABSTRACT

I studied in the laboratory and in the field the communication distance of the gomphocerine grasshopper Chorthippus biguttulus, which lives close to the ground in stony, short grass habitats. Using sound measurements and behavioural tests, I examined the frequency dependent attenuation and temporal degradation of the song pattern. Sound measurements (2–40 kHz) in the field revealed that excess attenuation increases with increasing frequency. Close to the ground, excess attenuation reaches 18 dB/m. On the basis of (i) excess attenuations, (ii) tympanic receptor threshold curves and (iii) song spectra, perception distances of female tympanic receptors for male songs and vice versa were calculated. Behavioural tests revealed that, especially in short and stony grass vegetation, the typical habitat of Ch. biguttulus, the temporal song pattern is strongly degraded. Thus, in the laboratory and in tall grass vegetation, sound attenuation was found to limit the communication distance. In contrast, in short grass vegetation, degradation of the temporal pattern was found to limit the communication distance of males listening to female songs. I argue that the exploitation of fast amplitude modulations for song recognition restricts the acoustic communication of grasshoppers to short distances (1–2.2 m). In this respect it seems adaptive to stridulate at low intensities.     

Courtship song analysis in two hybrid zones between sibling species of the <Emphasis Type="Italic">Chorthippus albomarginatus</Emphasis> group (Orthoptera,Gomphocerinae)

Two new hybrid zones between sibling species of the Chorthippus albomarginatus group were described on the basis of the courtship song analysis. Not only the sounds emitted but also the accompanying stridulatory movements of the hind legs were analyzed, which allowed the temporal parameters to be classified in a more reliable way. One hybrid zone between Ch. albomarginatus and Ch. karelini was found in Ulyanovsk and Samara Provinces of Russia. The other hybrid zone, presumably between Ch. karelini and Ch. oschei, was found in the protected Askania-Nova steppe area in Kherson Province of Ukraine. Based on comparison of the natural and laboratory hybrids, a hypothesis on the structure and dynamics of the hybrid zones is proposed.     

Typical ventilatory pattern of the intact locust is produced by the isolated CNS

Ventilatory rhythms of locusts are generated in the central nervous system (CNS). The primary oscillator or central pattern generator (CPG) is located in the metathoracic ganglion. We studied the different patterns of ventilation by recording long-term efferent discharges from the isolated metathoracic ganglion.Two different basic patterns occur: continuous ventilation and discontinuous ventilation. These patterns can be found in the isolated nerve cord as well as in intact animals. In intact animals sensory feedback usually elicits high frequency continuous ventilation as is the case in most physiological experiments. Many studies of ventilation-associated interneurones were performed under what we call stressed conditions i.e. with strong sensory feedback. Under these conditions many interneurones may be recruited which probably do not belong to the basic CPG. In isolated nerve cords of locusts we recognised the two basic types of ventilation. This provides an experimental approach to the origin of rhythmogenesis in ventilation. We can now examine single interneurones under less stressed or even discontinuous ventilatory conditions in the isolated CNS.We suggest the dominance of intrinsic rhythmogenesis of ventilation in the metathoracic ganglion of locusts.     

Projection areas and branching patterns of the tympanal receptor cells in migratory locusts,Locusta migratoria and Schistocerca gregaria

Summary In Locusta migratoria and Schistocerca gregaria, the projection areas and branching patterns of the tympanal receptor cells in the thoracic ganglia were revealed. Four auditory neuropiles can be distinguished on each side of the ventral cord, always located in the anterior part of the ring tract in each neuromere (two in the meta-, one in the meso-, and one in the prothoracic ganglion). Some of the receptor fibres ascend to the suboesophageal ganglion. There are distinct subdivisions within the auditory, frontal metathoracic and mesothoracic neuropiles. The arrangement of the terminal arborisations of the four types of tympanal receptor cells according to their different frequency-intensity responses is somatotopic and similar in the two ganglia. Here the receptor cells of type-1 form a restricted lateroventral arborisation. Cells of type-4 occupy the caudal part with a dorsorostral extension. Cells of type-2 and -3 arborise in a subdivision between both. Most of the stained low-frequency receptors (type-1, -2, and -3) terminate either in the metathoracic or, predominantly, in the mesothoracic ganglion. In contrast, the high-frequency cells (type-4) ascend to the prothoracic ganglion. The receptor fibres of the different types of receptor cells differ in diameter.Abbreviations aRT anterior part of the ring tract - cf characteristic frequency - MVT median ventral tract - SEG suboesophageal ganglion - SMC supramedian commissure - VMT ventral median tract - VIT ventral intermediate tract Supported by the Deutsche Forschungsgemeinschaft; part of program A7 in Sonderforschungsbereich 305 (Ecophysiology)     

新疆西部雏蝗属一新种记述（直翅目：网翅蝗科）

记述采自新疆西部网翅蝗科雏蝗属 Chorthippus 1新种,即新源雏蝗 Ch. xinyuanensis sp. nov.。新种近似于狭窝雏蝗Ch. foveatus Xia & Jin, 1982和长角雏蝗Ch. longicornis (Latreille),1804。与二者的主要区别为:前胸背板沟前区与沟后区等长;前胸背板侧隆线间最宽处为最狭处的1.7倍;前翅到达第6节背板中部(♂);中脉域约与肘脉域等宽(♂)。模式标本保存于陕西师范大学动物研究所标本室。     

A neural network-based analysis of acoustic courtship signals and female responses in <Emphasis Type="Italic">Chorthippus biguttulus</Emphasis> grasshoppers

In many animal species, male acoustic courtship signals are evaluated by females for mate choice. At the behavioural level, this phenomenon has been well studied. However, although several song characteristics have been determined to affect the attractiveness of a given song, the mechanisms of the evaluation process remain largely unclear. Here, we present a simple neural network model for analysing and evaluating courtship songs of Chorthippus biguttulus males in real-time. The model achieves a high predictive power of the attractiveness of artificial songs as assigned by real Chorthippus biguttulus females: about 87% of the variance can be explained. It also allows us to determine the relative contribution of different song characteristics to overall attractiveness and how each of the song components influences female responsiveness. In general, the obtained results closely match those of empirical studies. Therefore, our model may be used to obtain a first estimate of male song attractiveness and may thus complement actual testing of female responsiveness in the laboratory. In addition, the model allows including and testing novel song parameters to generate new hypotheses for further experimental studies. The supplemental material of this article contains the article’s data in an active, re-usable format.