Variation in nuptial gift quality in bush crickets (Orthoptera: Tettigoniidae)

Males of many insect species provide the female, during courtshipand copulation, with a nuptial gift consisting of a prey itemor synthesized material (e.g., spermatophores). The studiesperformed so far have mainly focused on effects of nuptial giftsize on male and female reproductive success. However, the qualityof the nuptial gift can differ substantially between taxa andmay potentially have a large impact on male and female reproductiveperformance. In this study the effects of. variation in dieton nuptial gift quality is investigated in several bush cricketspecies with different diets. The effect of diet on nuptialgift quality (e.g., protein in the spermatophylax) and femalereproductive output and, in turn, die effect of variation inspermatophylax quality on female reproductive output are investigated.Female reproductive output and male spermatophore size weremainly found to be influenced by differences in diet betweenspecies. Spermatophylax quality (i.e., protein concentration)was also correlated with differences in diet. There was a largevariation in protein content of the spermatophylax widiin aswell as between species. Moreover, larger spermatophylaxes hada lower protein concentration, indicating a possible trade-offbetween spermatophylax size and quality. Consequendy, productionof larger spermatophylaxes, required for protection of the male'ssperm carrying ampulla during insemination, can lead to a reducedprotein concentration, because the total amount of protein maybe limited. This pattern is also consistent with die idea diatthe spermatophylax functions primarily to ensure sperm transfer.Finally, there was no correlation between the amount of proteinin the spermatophylax and female reproductive output eitheracross diets or within each diet category, further supportingthe finding that female reproductive output is mainly affectedby differences in diet.     

Dispersal in a metapopulation of the bush cricket, Metrioptera bicolor (Orthoptera: Tettigoniidae)

1. I present a stochastic simulation model that describes individual movements of Metrioptera bicolor Philippi in a heterogeneous landscape, consisting of patches of suitable habitat surrounded by a matrix of unprofitable habitats. Although the model is parameterized with information about daily movement behaviour, it can generate spatially explicit predictions about inter-patch dispersal rates for much longer periods, e.g. one generation.
2. Long-term dispersal experiments were conducted to evaluate model predictions. Patch-specific emigration rates and the total distance moved by individuals could be predicted with satisfactory precision. Because of the stochastic nature of the model, it failed to predict which recipient patches emigrating individuals actually chose in a particular situation.
3. Spatially explicit simulations of the movement model were made for the whole natural distribution area of M. bicolor . The results suggest that emigration rates are negatively correlated with patch size. Local populations occurring on small patches may be more prone to extinction than those on large patches, by losing more emigrants than are compensated for by immigration.     

The function of sound in male spacing behaviour in bush-crickets (Tettigoniidae,Orthoptera)

This paper examines the spatial dynamics of an aggregation of singing male bush-crickets (Tettigoniidae) in respect to the degree of regularity between males. Our results establish that singing males of the genus Mygalopsis are regularly spaced within aggregations and that sound is involved in spacing. Attention is focussed on the male strategy of regular spacing within a widely dispersed aggregation in order to attract females reaching sexual maturity within the confines of that population. This is seen as an alternate to male aggregations attracting females from outside their boundary.     

Secondary structure and phylogenetic analysis of the internal transcribed spacers 1 and 2 of bush crickets (Orthoptera: Tettigoniidae: Barbitistini)

We inferred secondary structure models of the internal transcribed spacers (ITS) 1 and 2 of bush crickets using a combined comparative and thermodynamic approach. The inferred secondary structure models were used to account for interdependency of interacting nucleotides in a phylogenetic analysis of the bush cricket genus Poecilimon. Our analysis indicates that the two previously reported conformational structures (i.e., hairpin and ring) of ITS2 are likely to fold in bush crickets as well and that both predicted structures are similar to those proposed for other eukaryotes. Comparing predicted ITS1 secondary structure models proved to be difficult because of substantial variation in their nucleotide sequence length. Our study revealed that the phylogenetic signal of ITS1 and ITS2 is largely congruent with that preserved in the mitochondrial genes 16S rRNA, tRNA‐Val and 12S rRNA. The phylogenetic signal in both the nuclear and the mitochondrial genome question the monophyly of the genus Poecilimon: species of the genera Poecilimonella, Parapoecilimon, Polysarcus and Phonochorion consistently cluster within Poecilimon.     

Formation of the acrosome complex in the bush cricket Gampsocleis gratiosa (Orthoptera: Tettigoniidae)

The acrosome complex plays an indispensable role in the normal function of mature spermatozoa. However, the dynamic process of acrosome complex formation in insect remains poorly understood. Gampsocleis gratiosa Brunner von Wattenwyl possesses the typical characteristic of insect sperms, which is tractable in terms of size, and therefore was selected for the acrosome formation study in this report. The results show that acrosome formation can be divided into six phases: round, rotating, rhombic, cylindrical, transforming and mature phase, based on the morphological dynamics of acrosome complex and nucleus. In addition, the cytoskeleton plays a critical role in the process of acrosome formation. The results from this study indicate that: (1) glycoprotein is the major component of the acrosome proper; (2) the microfilament is one element of the acrosome complex, and may mediate the morphologic change of the acrosome complex; (3) the microtubules might also shape the nucleus and acrosome complex during the acrosome formation.     

Sensory basis for sound intensity discrimination in the bushcricket Requena verticalis (Tettigoniidae, Orthoptera)

The ability of the female bushcricket, Requena verticalis, to discriminate between two conspecific sound signals that differed in sound pressure level (SPL) was tested in a two-choice paradigm. Significant discrimination was achieved with a 2-dB difference. The property of each pair of receptors to establish binaural discharge differences was investigated in electrophysiological experiments. The threshold to the conspecific signal varies for each fibre from about 40 to 90 dB SPL, allowing for a range fractionation of the hearing organ. Each pair of receptors establishes significant binaural discharge differences only within a restricted intensity range about 10 dB above threshold. Based on a model of the intensity response function of a receptor the total discharge of the 22 receptors in both ears was calculated with monaural and binaural stimulation. The profile of receptors exhibiting significant discharge differences changes with increasing SPL, from the most sensitive fibres with a characteristic frequency between 12 kHz and 35 kHz at low SPLs to the least sensitive fibres at very low and high characteristic frequencies at medium to high SPLs. The discharge difference with an intensity difference of 2 dB is rather small (4% of the total receptor activity) and limited only to a few pairs of receptors. Accepted: 8 November 1997     

Colour polymorphism in Ephippiger ephippiger (Orthoptera, Tettigoniidae)

Colour in the Ephippiger ephippiger complex varies with the geographical distribution and with rearing density. In the W European subspecies E. e. vitium , wild insects from northern and eastern parts of the range tend to have green tergites with relatively inconspicuous banding, whereas those from S France have conspicuously pale banded dark-green or brown tergites. These forms represent the ends of a continuum and there is no zone of distinction. However, the E Pyrenean subspecies, E. e. cunii , lacks the broad banding of its neighbouring E. e. vitium. The tergites of laboratory cultured insects of these stocks when reared in isolation are distinctly green but when reared together become progressively brown. The darkness of the brown is density dependant, so that at high densities the tergites may become almost black. These colour changes are irreversible. Adult insects also become darker with sexual maturity and after contact on mating. Wild-caught E. e. ephippiger from Italy and Yugoslavia have green tergites without obvious banding. Colour changes have not been found or induced in this subspecies. The significance of the colour change is considered and although firm data are wanting, circumstantial evidence suggests a deliberate shift to an aposematic or pseudoaposematic colour pattern.     

Ecology and sound signaling of relict katydid Deracantha onos (Pallas, 1772) (Orthoptera, Tettigoniidae, Bradyporinae)

Life history and acoustic signaling of a Central Asian species Deracantha onos (Pall.) are described. Males and females produce calling signals and protest sounds. For the first time, electronograms of stridulatory files, oscillograms, and frequency spectra of some acoustic signals are given.     

Effect of sound signals on spontaneous activity in grasshopper interneurons (Orthoptera,Tettigonidae)

According to one of hypotheses proposed for explaining mechanisms of sound signal recognition in insects, their CNS contains a group of rhythmically active neurons that function as a reference standard for comparison with perceived acoustic information. To check this hypothesis, the spontaneous neuronal activity and its changes in perception of conspecific and heterospecific signals (CS and HS) were analyzed in the CNS of two sympatric grasshopper species Tettigonia cantans and Metrioptera roeselii. The activity of individual neurons was assayed in fixed and freely moving insects. The results of the experiment have shown that in the thoracic part of the CNS there is a group of rhythmically active neurons that do not directly respond to sound signal but readjust their impulses under effect of its action. On presentation of CS the following reactions were observed: attenuation or enhancement of impulses; stabilization or destabilization of rhythm; regular increase or decrease in interspike intervals; phasic readjustments leading to synchronization of impulses with sound stimuli (pulses). No similar alterations were usually produced by HS; still, if they did appear, they were less pronounced or of opposite direction. These data indicate that the grasshopper auditory system affects markedly the rhythmically active neurons, their reaction depending considerably on temporal organization of sound signals. Selectivity of these reactions allows us to suggest that the rhythmically active neurons are directly related to the neuronal networks providing the sound signal recognition.Translated from Zhurnal Evolyutsionnoi Biokhimii i Fiziologii, Vol. 40, No. 6, 2004, pp. 531–538.Original Russian Text Copyright © 2004 by Zhantiev, Korsunovskaya, Chukanov.To the 100-Anniversary of A. K. VoskresenskayaThis revised version was published online in April 2005 with a corrected cover date.     

Ultrasonic startle behavior in bushcrickets (Orthoptera; Tettigoniidae)

1. In the present work, we show that in flight, bushcrickets not previously known to respond to ultrasound alter their flight course in response to ultrasonic stimuli. Such stimuli elicit in flying Neoconocephalus ensiger an extension of the front and middle legs along the body and a rapid closure of all 4 wings (Fig. 1). This is a short latency acoustic startle response to ultrasound, consistent with acoustic startle responses of other insects. 2. The percentage of trials on which acoustic startle responses were elicited was maximum (90%) for sound frequencies ranging from 25 to at least 60 kHz. No acoustic startle response was observed at frequencies of 5 or 10 kHz (Fig. 2). The threshold for the response was roughly 76 dB between 25 to 60 kHz (Fig. 2) and the behavioral latency was 45 ms (Fig. 3). Recordings from flight muscles show that they cease discharging during the acoustic startle response (Fig. 4). 3. The characteristics of the acoustic startle response match those of an auditory interneuron called the T-neuron. The frequency sensitivity of this neuron is greatest for sound frequencies ranging from 13 to 60 kHz (Fig. 6). Moreover, we found that the neuron produces many more spikes to ultrasound (30 kHz) of increasing intensities than to a conspecific communication sound, whose dominant frequency is 14 kHz (Fig. 7).     

Measuring sexual selection on females in sex‐role‐reversed Mormon crickets (Anabrus simplex,Orthoptera: Tettigoniidae)

Although many studies examine the form of sexual selection in males, studies characterizing this selection in females remain sparse. Sexual selection on females is predicted for sex‐role‐reversed Mormon crickets, Anabrus simplex, where males are choosy of mates and nutrient‐deprived females compete for matings and nutritious nuptial gifts. We used selection analyses to describe the strength and form of sexual selection on female morphology. There was no positive linear sexual selection on the female body size traits predicted to be associated with male preferences and female competition. Instead, we detected selection for decreasing head width and mandible length, with stabilizing selection as the dominant form of nonlinear selection. Additionally, we tested the validity of a commonly used instantaneous measure of mating success by comparing selection results with those determined using cumulative mating rate. The two fitness measures yielded similar patterns of selection, supporting the common sampling method comparing mated and unmated fractions.     

Functional forewing morphology and stridulation in crickets (Orthoptera, Grylloidea)

Forewing morphology and infrastructure are analysed in three cricket species ( Gryllus campestris, Oecanthus pellucens and Lerneca fuscipennis ) and checked in 20 other genera. A strong dorsoventral asymmetry is demonstrated for the first time. The upper side of the tegmina is covered with hexagonal, more or less high crests forming reliefs. On the lower side, annulate, flat and thick veins exist. The distribution of the hexagons and that of the different vein types is uneven on the forewing surfaces. Their significance in forewing functional morphology is discussed in relation to stridulation and to current knowledge on cricket sound production mechanisms. Their extent and distribution, together with the number and strength of the veins and the surface of wing cells, could account for the vibrational characteristics of the cricket forewing and explain the diverse results obtained by several authors on Gryllus and Oecanthus .     

Physiological aspects of sound communication in crickets (Gryllus campestris L.)

Summary An extremely elaborate performance, involving endogenous timing with both tidal and lunar frequencies, has been recorded in the locomotor activity of an adult specimen of the intertidal isopod,Excirolana chiltoni. During two months of observation, under constant, non-tidal conditions, this animal showed a persistent tidal rhythm in its swimming activity. Bursts of activity were initially well synchronized with times of tide crest on the shore. The average free-running period of the tidal rhythm was about 24 h 55 min, i.e. about 5 minutes longer than the average period of the tides; thus, the loss of synchrony with the concurrent tides was very gradual. The amount of activity per burst showed a conspicuous pattern of variation, a periodic amplitude modulation which paralleled, in detail, the complex lunar cycle of changes in height of high tide. The free-running period of the bimodal, circa-lunar rhythm of amplitude modulation was one or two days longer than the natural 29-day lunar cycle of tide heights.Each feature of this recording has been qualitatively replicated in activity records from other individuals of this species. Freshly-collectedExcirolana generally show spontaneous bursts of activity at times of tide crest, bursts which are repeated as a persistent tidal rhythm, the period of which commonly departs by only a few minutes from that of the natural tidal cycle. Superimposed on the tidal rhythm is an endogenous monthly pattern of amplitude modulation, which alters the amount of activity per burst. This circa-lunar rhythm has a free-running period between about 26 and 33 days, and generally leads to maximum activity on days of highest of high tides. The net result of the tidal and lunar rhythms is an activity pattern which permits the isopods to recapitulate, in great detail, certain significant ecological aspects of the mixed, semi-diurnal tidal regime of California.The experimental data are not compatible with the hypothesis that uncontrolled environmental factors, such as vibrations from waves, were responsible for the rhythmic behavior of the animals. Neither do the data support the hypothesis that beats between the observed tidal rhythm and a hidden daily or circadian rhythm were responsible for the observed circa-lunar rhythm. Furthermore, the pattern of the circa-lunar rhythm cannot be accounted for by a single monthly oscillation in the excitability of the animals, such as might be mediated by changes in the level of an excitatory or inhibitory hormone in the circulatory system.     

Two functional types of attachment pads on a single foot in the Namibia bush cricket Acanthoproctus diadematus (Orthoptera: Tettigoniidae)

Insects have developed different structures to adhere to surfaces. Most common are smooth and hairy attachment pads, while nubby pads have also been described for representatives of Mantophasmatodea, Phasmida and Plecoptera. Here we report on the unusual combination of nubby and smooth tarsal attachment structures in the !nara cricket Acanthoproctus diadematus. Their three proximal tarsal pads (euplantulae) have a nubby surface, whereas the most distal euplantula is rather smooth with a hexagonal ground pattern resembling that described for the great green bush-cricket Tettigonia viridissima. This is, to our knowledge, the first report on nubby euplantulae in Orthoptera and the co-occurrence of nubby and smooth euplantulae on a single tarsus in a polyneopteran species. When adhering upside down to a horizontal glass plate, A. diadematus attaches its nubby euplantulae less often, compared to situations in which the animal is hanging upright or head down on a vertical plate. We discuss possible reasons for this kind of clinging behaviour, such as morphological constrains, the different role of normal and shear forces in attachment enhancement of the nubby and smooth pads, ease of the detachment process, and adaptations to walking on cylindrical substrates.     

Structure of the stridulation ofOrchelimum (Orthoptera: Tettigoniidae)

Summary The structure of the stridulation was investigated by re-playing tape-recordings at very slow speed. The findings were corrobrated by sonograms and mingograms.The central part of the song is the ripple, a fast succession of syllables around which isolated syllables (clicks) are distributed according to species and circumstances. The rate of syllables in the ripple is a linear function of temperature.A quantitative expression for the stridulatory activity is the actual number of syllables per time unit, including pauses. By changes in the combination of elements, at leastO. agile is able to increase the output of syllables four to six times.This work was made possible by a grant from the Carlsberg Foundation to whom my most sincere thanks are due. —As I do not have advanced equipment for sound analysis, I am very much indebted to Dr. Bondesen and cand. sci. Poul Hansen, Bioakustisk Laboratorium, Naturhistorisk Museum, Aarhus, Denmark, and Mr. W.B. Broughton and Dr. M. Samways, Animal Acoustic Unit, City of London Polytechnic, London, for analysing part of the material by sonograms and mingograms. The very valuable help of Dr. Th.J. Walker, University of Florida, Gainesville, Florida, in identifying the species is gratefully acknowledged. For friendly discussions and linguistic corrections my best thanks are due to H.T. Evans and F.D.S. Evans.     

Effect of temperature on auditory receptor functions in crickets (Orthoptera,Tettigoniodea)

By electrophysiological methods, effect of temperature on cricket tympanal organ functions was studied. Activity of auditory receptors was recorded intracellularly in the 5th nerve of I thoracic ganglion in Tettigonia cantans, Metrioptera roeselii, M. bicolor, Platycleis albopunctata, Pholidoptera griseoaptera, and Phaneroptera falcata. The temperature was changed in the range from 17 to 34° C. Heating of the tympanal organ to 30–32°C led to a decrease of impulse amplitude, shortening of their duration, an increase of sensitivity, of the burst instantaneous frequency, and of the number of impulses in the responses as well as to a decrease of latent periods (LP) of receptor reaction. The optimal frequency in all studied cells did not change, although the range of perceived frequencies was enlarged. The frequency threshold curve of receptor either was shifted down along the ordinate scale without changes of its shape or the thresholds at various frequencies decreased non-uniformly. Thus, the obtained data indicate the absence of changes in the frequency tuning of the auditory receptors with changes of temperature.