Grasshopper Chorthippus Biguttulus Research Articles

Motorway age is linked to larger body size, but not song carrier frequency, in male grasshoppers from roadside populations

Producing calls with increased minimum carrier frequency is well documented in sound communicating species confronted with noise pollution, possibly helping them to avoid acoustic masking of low-frequency signals. However, the lack of studies on invertebrates limits our understanding of the potentially adverse effects of anthropogenic noise on natural populations. While males of the grasshopper Chorthippus biguttulus are known to produce courtship signals with elevated low-frequency local maxima (LFLM) in roadside populations, previous studies provided no insight into morphological traits underlying LFLM shifts. Although developmental plasticity was identified as one main factor accounting for elevated LFLM, an additional role for a more hard-wired trait architecture was proposed, possibly as a result of adaptation to traffic noise. Our current study therefore aims to assess (1) whether the position of LFLM is related to male body size, (2) whether body size is correlated with motorway age, and (3) whether the position of LFLM is correlated with motorway age in C. biguttulus males from roadside populations. In addition to substantial variation in LFLM among C. biguttulus males, we found that larger males produced signals with lower LFLM, suggesting a potential role in female choice as a predictor of male quality. While we found no significant correlation between LFLM and motorway age, C. biguttulus males were larger near older motorway sections. This positive correlation may be due to several reasons, including: (1) higher nutrient concentration and availability in plant tissues due to eutrophication of roadside habitats; (2) temporal succession of male size phenotypes during colonization processes; and/or (3) selection for larger body size in roadside populations. Our results highlight the multifaceted and often complex nature of the relationships between morphology, signal traits and anthropogenic pressures on sound communication in invertebrates.

Direct and indirect genetic effects on reproductive investment in a grasshopper.

A fundamental part of the quantitative genetic theory deals with the partitioning of the phenotypic variance into additive genetic and environmental components. During interaction with conspecifics, the interaction partner becomes a part of the environment from the perspective of the focal individual. If the interaction effects have a genetic basis, they are called indirect genetic effects (IGEs) and can evolve along with direct genetic effects. Sexual reproduction is a classic context where potential conflict between males and females can arise from trade-offs between current and future investments. We studied five female fecundity traits, egg length and number, egg pod length and number and latency to first egg pod, and estimated the direct and IGEs using a half-sib breeding design in the grasshopper Chorthippus biguttulus. We found that the male IGEs were an order of magnitude lower than the direct genetic effects and were not significantly different from zero. However, there was some indication that IGEs were larger shortly after mating, consistent with the idea that IGEs fade with time after interaction. Female direct heritabilities were moderate to low. Simulation shows that the variance component estimates can appear larger with less data, calling for care when interpreting variance components estimated with low power. Our results illustrate that the contribution of male IGEs is overall low on the phenotypic variance of female fecundity traits. Thus, even in the relevant context of sexual conflict, the influence of male IGEs on the evolutionary trajectory of female reproductive traits is likely to be small.

Robustness of an innate releasing mechanism against degradation of acoustic communication signals in the grasshopper Chorthippus biguttulus.

Noise is a challenge for animals that use acoustic communication to find a mate. A potent source of noise in animal communication is that arising from other conspecific signals, whose co-occurrence can result in extensive interference-evident as the so called "cocktail-party problem"-that may affect the receiver mechanisms to detect potential mates. We studied grasshopper females to explore how modifications of the song pattern influence song recognition. First, we degraded an attractive model song with random fluctuations of increasing amplitudes out of different frequency bands, and determined "critical degradation levels" at which the females ceased to respond. A masker band with frequencies between 0 and 200Hz, which covers the frequency range of the natural song envelope, was by 3-5dB more destructive in hampering signal recognition than frequencies above 200Hz. As second approach, we applied temporal disturbances such as accentuations or gaps at different positions within the song subunits and observed how response behavior was affected. Accentuations at subunit start increased, whereas those in the midst or at the end of a subunit reduced attractiveness. Gaps at these positions had diverse effects. The results are discussed with respect to neuronal filtering.

Relative weighting of acoustic information during mating decisions in grasshoppers indicates signatures of sexual selection

The decision with whom to mate is crucial in determining an individual’s fitness and is often based on the evaluation of visual or acoustic displays produced during courtship. Accordingly, the algorithms for evaluating such courtship signals are shaped by sexual selection and should reflect the expected benefits and costs of mating: signals bearing heterospecific features should be rapidly rejected, since mating would produce no fertile offspring, while signals resembling conspecific ones should be weighted proportional to mate quality. We test these hypotheses in females of the grasshopper Chorthippus biguttulus who assess males by their song, which is produced as a sequence of subunits with species and individual specific signatures. We present mixed sequences of subunits with conflicting cues and use a computational model of decision-making to infer how sensory information is weighted and integrated over the song. Consistent with our hypothesis, females do weight sensory cues according to the expected fitness benefits/costs: heterospecific subunits are weighted particularly negatively and lead to a rejection of the male early in the song. Conspecific subunits are weighted moderately, permitting a more complete evaluation of the full song. However, there exists an overall negative bias against mating, possible causes of which are discussed.

Transcriptome profiling of ontogeny in the acridid grasshopper Chorthippus biguttulus.

Acridid grasshoppers (Orthoptera:Acrididae) are widely used model organisms for developmental, evolutionary, and neurobiological research. Although there has been recent influx of orthopteran transcriptomic resources, many use pooled ontogenetic stages obscuring information about changes in gene expression during development. Here we developed a de novo transcriptome spanning 7 stages in the life cycle of the acridid grasshopper Chorthippus biguttulus. Samples from different stages encompassing embryonic development through adults were used for transcriptomic profiling, revealing patterns of differential gene expression that highlight processes in the different life stages. These patterns were validated with semi-quantitative RT-PCR. Embryonic development showed a strongly differentiated expression pattern compared to all of the other stages and genes upregulated in this stage were involved in signaling, cellular differentiation, and organ development. Our study is one of the first to examine gene expression during post-embryonic development in a hemimetabolous insect and we found that only the fourth and fifth instars had clusters of genes upregulated during these stages. These genes are involved in various processes ranging from synthesis of biogenic amines to chitin binding. These observations indicate that post-embryonic ontogeny is not a continuous process and that some instars are differentiated. Finally, genes upregulated in the imago were generally involved in aging and immunity. Our study highlights the importance of looking at ontogeny as a whole and indicates promising directions for future research in orthopteran development.

Exploring the hidden landscape of female preferences for complex signals

A major challenge in evolutionary biology is explaining the origins of complex phenotypic diversity. In animal communication, complex signals may evolve from simpler signals because novel signal elements exploit preexisting biases in receivers' sensory systems. Investigating the shape of female preference functions for novel signal characteristics is a powerful, but underutilized, method to describe the adaptive landscape potentially guiding complex signal evolution. We measured female preference functions for characteristics of acoustic appendages added to male calling songs in the grasshopper Chorthippus biguttulus, which naturally produces only simple songs. We discovered both hidden preferences for and biases against novel complex songs, and identified rules governing song attractiveness based on multiple characteristics of both the base song and appendage. The appendage's temporal position and duration were especially important: long appendages preceding the song often made songs less attractive, while following appendages were neutral or weakly attractive. Appendages had stronger effects on songs of shorter duration, but did not restore the attractiveness of very unattractive songs. We conclude that sensory biases favor, within predictable limits, the evolution of complex songs in grasshoppers. The function-valued approach is an important tool in determining the generality of these limits in other taxa and signaling modalities.

Noise affects the shape of female preference functions for acoustic signals.

The shape of female mate preference functions influences the speed and direction of sexual signal evolution. However, the expression of female preferences is modulated by interactions between environmental conditions and the female's sensory processing system. Noise is an especially relevant environmental condition because it interferes directly with the neural processing of signals. Although noise is therefore likely a significant force in the evolution of communication systems, little is known about its effects on preference function shape. In the grasshopper Chorthippus biguttulus, female preferences for male calling song characteristics are likely to be affected by noise because its auditory system is sensitive to fine temporal details of songs. We measured female preference functions for variation in male song characteristics in several levels of masking noise and found strong effects of noise on preference function shape. The overall responsiveness to signals in noise generally decreased. Preference strength increased for some signal characteristics and decreased for others, largely corresponding to expectations based on neurophysiological studies of acoustic signal processing. These results suggest that different signal characteristics will be favored under different noise conditions, and thus that signal evolution may proceed differently depending on the extent and temporal patterning of environmental noise.

Genome size variation affects song attractiveness in grasshoppers: evidence for sexual selection against large genomes.

Genome size is largely uncorrelated to organismal complexity and adaptive scenarios. Genetic drift as well as intragenomic conflict have been put forward to explain this observation. We here study the impact of genome size on sexual attractiveness in the bow-winged grasshopper Chorthippus biguttulus. Grasshoppers show particularly large variation in genome size due to the high prevalence of supernumerary chromosomes that are considered (mildly) selfish, as evidenced by non-Mendelian inheritance and fitness costs if present in high numbers. We ranked male grasshoppers by song characteristics that are known to affect female preferences in this species and scored genome sizes of attractive and unattractive individuals from the extremes of this distribution. We find that attractive singers have significantly smaller genomes, demonstrating that genome size is reflected in male courtship songs and that females prefer songs of males with small genomes. Such a genome size dependent mate preference effectively selects against selfish genetic elements that tend to increase genome size. The data therefore provide a novel example of how sexual selection can reinforce natural selection and can act as an agent in an intragenomic arms race. Furthermore, our findings indicate an underappreciated route of how choosy females could gain indirect benefits.

Transgenerational effects of diet environment on life-history and acoustic signals of a grasshopper

Phenotypic plasticity can be due to environmental conditions experienced during an individual’s lifetime, but can also be based on parental effects, that is the responses of the parental generation to their own environment. Such transgenerational responses might be adaptive by allowing fine-tuning of offspring traits to the present environment. We examined whether the parental and offspring diet affect offspring life history and sexually selected acoustic signal traits in the grasshopper Chorthippus biguttulus. In a full factorial design, parents and offspring were reared on high-quality or poor-quality diet. We found significant positive effects of parental high-quality food on offspring developmental time, body mass, song amplitude in adult males, and weight of egg pods in adult females. In all cases, these effects were larger than direct effects of the diet environment experienced during ontogeny, even though some of these were significant, too. Interactions between parental and ontogenetic treatments were all nonsignificant, indicating that offspring traits are not adjusted to enhance performance on the same diet as the parent. We conclude that parental effects are unexpectedly stronger than effects of the offspring diet environment in C. biguttulus. These parental effects do not seem to constitute adaptive phenotypic plasticity, but nevertheless show that the nutritional environment of the parents has a large influence on traits in C. biguttulus grasshoppers. Key words: acoustic signal traits, grasshoppers, lifehistory traits, parental effects, phenotypic plasticity . [Behav Ecol]

Song characteristics and morphological traits in four populations of the grasshopper Chorthippus biguttulus L.

We investigated four populations of the grasshopper Chorthippus biguttulus with respect to differences in morphological traits and characteristics of their communication signals. A special focus was laid on possible correlations between morphological and song traits of males that could be used by females to infer quality cues of potential mates. We also tested whether females exhibit preferences for males of their own population. Specific song features (onset accentuation, offset, syllable period) of males-but not of females-differed between populations. We observed size differences both in males and females from different populations, but the size ranks of the two sexes were not always correlated. Environmental factors appear to have a strong influence on different size traits, compared to genetic origin. In all populations a specific song feature, the accentuation of syllable onsets, showed a similar correlation with a morphological trait, hind leg size, but its correlation with other size indicators sometimes differed in sign. Females did not prefer songs of males from their own population. The best predictor for song attractiveness was-unexpectedly-not the onset accentuation but the offset depth.

Limited condition dependence of male acoustic signals in the grasshopperChorthippus biguttulus

In many animal species, male acoustic signals serve to attract a mate and therefore often play a major role for male mating success. Male body condition is likely to be correlated with male acoustic signal traits, which signal male quality and provide choosy females indirect benefits. Environmental factors such as food quantity or quality can influence male body condition and therefore possibly lead to condition-dependent changes in the attractiveness of acoustic signals. Here, we test whether stressing food plants influences acoustic signal traits of males via condition-dependent expression of these traits. We examined four male song characteristics, which are vital for mate choice in females of the grasshopper Chorthippus biguttulus. Only one of the examined acoustic traits, loudness, was significantly altered by changing body condition because of drought- and moisture-related stress of food plants. No condition dependence could be observed for syllable to pause ratio, gap duration within syllables, and onset accentuation. We suggest that food plant stress and therefore food plant quality led to shifts in loudness of male grasshopper songs via body condition changes. The other three examined acoustic traits of males do not reflect male body condition induced by food plant quality.

Grasshopper calling songs convey information about condition and health of males

Females of the grasshopper Chorthippus biguttulus invest much more in the offspring than do males. As a consequence, females are the more selective sex and exert a sexual selection on males by responding to the songs of certain conspecific males while rejecting others. What kind of information about the sender may a female obtain from a male's song, in addition to its species identity? We searched for correlations between a series of song features and morphometric parameters of individual males. In addition, also the immunocompetence of males was assessed by implanting small pieces of nylon thread. We found significant, positive correlations between certain song characteristics and indicators of male size and immunocompetence. Thus, grasshopper females may--in principle--be able to judge a male's condition and health from the acoustic signals he produces.

From molecule to sexual behavior: The role of the neuropentapeptide proctolin in acoustic communication in the male grasshopper Chorthippus biguttulus

Acoustic communication in male Chorthippus biguttulus is a suitable behavioral model to explore the physiological effects and underlying molecular mechanisms of identified neuropeptides. Proctolin plays a modulatory role in a neuronal circuit controlling sexual behavior in these insects. Activation of proctolin receptors triggers courtship singing (the second level of excitation in sexual behavior) that is preceded by call singing triggered by muscarinic acetylcholine receptor activation. The pharmacological studies presented here revealed that the Phospholipase C pathway was involved in courtship singing since neomycin and Li + strongly inhibited proctolin-stimulated singing. In addition, injecting phorbol ester into proctolin-sensitive neural sites only elicited stridulation. This confirms that proteinkinase C can mediate the effects of Phospholipase C activation in this model. These results partially clarify the molecular mechanisms in the decision making brain center that controls sexual behavior in these insects.

The role of frequency, phase and time for processing of amplitude modulated signals by grasshoppers

Acoustic signals consist of pressure changes over time and can thus be analyzed in the frequency- or in the time-domain. With behavioural experiments we investigated which frequency components (FC) are necessary for the recognition of the periodic envelope of the conspecific song by females of the grasshopper Chorthippus biguttulus. Further, we determined up to which frequency component phase information is required which would indicate processing in the time domain. Responses of females revealed that signals composed of FC between 10 and 50 Hz are sufficient for recognition of the song envelope. A systematic reduction in the number of FC showed that no single frequency component was required; signals without the fundamental frequency were still highly attractive and only three FC may be sufficient for song recognition. Phase changes for frequencies up to 40 Hz strongly changed the attractiveness of song signals but only little at 50 Hz. Females were also tested with rectangular signals in which pause duration was varied. Evidently, and despite the high attractiveness of song signals with a "missing fundamental", females evaluated the attractiveness of signals in the time-domain, since the selectivity for pause duration predicted the responses to signals composed from FC well.

Indirect benefits for choosy female grasshoppers ( Chorthippus biguttulus)?

Since direct benefits are likely to be absent in the grasshopper Chorthippus biguttulus, indirect genetic benefits are a potential explanation for costly female preference. Choosy females may improve their fitness in terms of enhanced attractiveness of sons alone or additionally by improved viability of offspring. We tested the predictions of these two hypotheses by comparing attractiveness-related song traits and viability in offspring of attractive and unattractive grasshopper males. The experiment was conducted with larvae reared under semi natural lab conditions in one year and under natural conditions in the field in the following year. If reared under natural conditions no significant differences in viability and song traits between offspring of attractive and unattractive males could be found. Offspring reared in the lab produced calling songs with a significantly more exact song rhythm when sired by attractive males than offspring of unattractive males. Offspring of attractive males should thus have a theoretical advantage in mate choice, which, however, did not translate into higher attractiveness values in acoustic female choice experiments. Therefore our experiments could not resolve whether female choice in C. biguttulus evolved according to the sexy son hypothesis. Since viability in offspring of attractive males did not differ from offspring of unattractive males, “good genes” seems unlikely to be the underlying mechanism of female choice.

Species Recognition Influences Female Mate Preferences in the Common European Grasshopper (Chorthippus biguttulus Linnaeus, 1758)

AbstractSpecies recognition and intraspecific mating preferences constitute two basic aspects of animal communication. Both can be considered as variations in response to signals and it has been suggested that they represent a continuum. Selection on species recognition could therefore influence intraspecific mating preferences. We show that females of the common European grasshopper Chorthippus biguttulus prefer conspecific male signals that can be distinguished more reliably from sympatrically occurring heterospecific signals. This suggests that in C. biguttulus, sexual selection might be influenced by pleiotropic effects from species recognition. The results show how the heterospecific signal environment could have determined why and in which direction specific traits become sexually selected.

Local adaptation and sexual selection: a reciprocal transfer experiment with the grasshopper Chorthippus biguttulus

Immigration into locally adapted populations has been suggested, among other potential causes, to maintain genetic variance in fitness necessary for good-genes models. Using a reciprocal transplant experiment we examined whether females prefer native to transferred males in the grasshopper Chorthippus biguttulus. On average, native and transferred males did not differ in their attractiveness, measured as female response rate to playbacks of male acoustic courtship signals. In line with this result, we found no significant effect of transfer on body size, condition, fluctuating asymmetry or song traits. However, the reciprocal transplant experiment showed that environmental conditions did influence body condition and maximum loudness of the calling song, but that the genetic origin of male grasshoppers had no significant effect on any of the analysed traits.

Acoustic communication in a duetting grasshopper: receiver response variability, male strategies and signal design

In the duetting grasshopper Chorthippus biguttulus, a female's decision to reply to a conspecific male is based on the evaluation of a number of features of the male's song, which consists of uninterrupted syllables separated by pauses. Female responses are tuned to a restricted range of pause durations. However, males produce songs with noisy rather than silent pauses, which should make the measurement of pause durations more difficult for the female. We examined the adaptive value of these noisy pauses by testing female responses to (1) pairs of natural phrases, which differed only with respect to clear or noisy syllable pauses, and (2) synthetic phrases, in which the syllable onset accentuations and noise levels in the pauses were systematically varied. There was considerable variation between females, both in their preference for clear or noisy pauses in natural phrases, and in the optimal combinations of syllable onset accentuations and noise levels in pauses that they preferred in synthetic phrases. The response profiles of individual females were consistent. The experiments with synthetic phrases showed that, on average, females preferred more extreme values of syllable onset accentuations than were present in male songs. Noisy pauses increased the range of syllable pause durations accepted by females. The results suggest that noisy pauses could buffer signallers against the negative consequences of both signal degradation during transmission and extreme receiver choosiness.

Acoustic communication in a duetting grasshopper: receiver response variability, male strategies and signal design

In the duetting grasshopper Chorthippus biguttulus , a female's decision to reply to a conspecific male is based on the evaluation of a number of features of the male's song, which consists of uninterrupted syllables separated by pauses. Female responses are tuned to a restricted range of pause durations. However, males produce songs with noisy rather than silent pauses, which should make the measurement of pause durations more difficult for the female. We examined the adaptive value of these noisy pauses by testing female responses to (1) pairs of natural phrases, which differed only with respect to clear or noisy syllable pauses, and (2) synthetic phrases, in which the syllable onset accentuations and noise levels in the pauses were systematically varied. There was considerable variation between females, both in their preference for clear or noisy pauses in natural phrases, and in the optimal combinations of syllable onset accentuations and noise levels in pauses that they preferred in synthetic phrases. The response profiles of individual females were consistent. The experiments with synthetic phrases showed that, on average, females preferred more extreme values of syllable onset accentuations than were present in male songs. Noisy pauses increased the range of syllable pause durations accepted by females. The results suggest that noisy pauses could buffer signallers against the negative consequences of both signal degradation during transmission and extreme receiver choosiness.

Influence of amplitude modulated noise on the recognition of communication signals in the grasshopper Chorthippus biguttulus.

The detection of acoustic communication signals in the presence of sinusoidally amplitude modulated noise was investigated in males of the grasshopper Chorthippus biguttulus. The auditory system of grasshoppers exhibits only poor spectral resolution. Hence, these animals are ideally suited to investigate noise tolerance in a system operating in the temporal domain. As a sensitive indicator for signal recognition the conspicuous phonotactic turning responses of males were recorded. The main result was that noise modulated at low frequencies (1.5-5 Hz) did not impair recognition compared to a unmodulated noise. With long stimuli even a moderate improvement of noise tolerance was observed, an effect that can probably be attributed to the existence of long troughs at low modulation frequencies during which the masking of the signal was reduced. Higher modulation frequencies (15-150 Hz), however, rendered detection and recognition increasingly difficult, due to a strong interference of the sound pulses of the masking noise with the syllable-pause structure of the species-specific signals. There are no indications for the operation of mechanisms analogous to comodulation masking release as found in vertebrates, nor for a spatial release from masking.