Pharmacological brain stimulation releases elaborate stridulatory behaviour in gomphocerine grasshoppers – conclusions for the organization of the central nervous control

Grasshoppers produce a variety of sounds generated by complex movements of the hindlegs. Stridulation, performed in the context of partner finding, mating and rivalry, can be released by pressure injection of cholinergic agonists into the protocerebrum. Particularly stimulation with muscarinic agonists induced long-lasting stridulation that resembled the natural behaviour to an astonishing degree, not only with respect to their temporal structure and right/left coordination, but also to changes in the song sequences according to the progress of courtship stridulation, even including accessory movements of other parts of the body. According to the complexity of their stridulatory behaviour ten gomphocerine species were chosen for this comparative study. The results indicate that the protocerebrum fulfils two important tasks in the control of stridulation: (1) it integrates sensory input relevant to stridulation that represents a certain behavioural situation and internal state of arousal, and (2) it selectively activates and deactivates the thoracic networks that generate the appropriate movement and sound patterns. With the knowledge of the natural behaviour and the accessibility to pharmacological and electrophysiological studies, the cephalic control system for stridulation in grasshoppers appears to be a suitable model for how the brain selects and controls appropriate behaviours for a given situation.     

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     

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.     

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.     

Identified descending brain neurons control different stridulatory motor patterns in an acridid grasshopper

During courtship sequences male grasshoppers of the species Omocestus viridulus successively perform with their hindlegs three different stridulatory movement patterns: ordinary stridulation, hindleg shaking and precopulatory movements. Microinjection of acetylcholine into protocerebral neuropil regions can either elicit complete courtship sequences or evoke one of the three motor patterns. Intracellular recordings and stainings revealed three types of descending brain neurons: B-DC-3, B-DC-4 and B-DC-5. All three types of interneurons have a medial axon position in the connectives. They cross the midline of the protocerebrum and exhibit a profuse arborization pattern within the medial dorsal protocerebral neuropil. Stimulation of each type of interneuron specifically elicits one particular motor pattern of courtship behaviour. Courtship of the grasshopper O. viridulus may therefore be controlled by successive activation of these descending brain neurons. Accepted: 27 September 1996     

Frequency as a releaser in the courtship song of two crickets,Gryllus bimaculatus (de Geer) and Teleogryllus oceanicus: a neuroethological analysis

1. The courtship behavior of male field crickets, Gryllus bimaculatus (De Geer) and Teleogryllus oceanicus, is a complex, multimodal behavioral act that involves acoustic signals (a courtship song; Fig. 1A,B). The dominant frequency is 4.5 kHz for T. oceanicus song (Fig. 1A) and 13.5 kHz for G. bimaculatus (Fig. IB).
2. When courting males are deprived of their courtship song by wing amputation, their courtship success declines markedly but is restored when courting is accompanied by tape-recordings of their courtship songs or a synthetic courtship song with only the dominant frequency of the natural song; other naturally occurring frequency components are ineffective for restoring mating success (Figs. 4, 5).
3. It has been suggested that an identified auditory interneuron, AN2, plays a critical role in courtship success. Chronic recordings of AN2 in an intact, tethered female show that AN2's response to the natural courtship song and synthesized songs at 4.5 and 13.5 kHz is similar in T. oceanicus. By contrast, in G. bimaculatus, AN2's response to the natural courtship song and synthesized song at 13.5 kHz, but not at 4.5 kHz, is similar (Figs. 2,3).
4. In behavioral experiments, playback of a 30 kHz synthetic courtship song in G. bimaculatus does not restore courtship success, yet this same stimulus elicits as strong a response from AN2 as does the normal courtship song (Fig. 6). Thus, contrary to earlier work by others, we conclude AN2 is not, by itself, a critical neural link in the courtship behavior of these two species of crickets.

     

The Effect of Male Competition on the Courtship Song of Drosophila melanogaster

The courtship song of Drosophila has been extensively used as a model system for studies of sexual selection and species recognition. Traditionally, the courtship song has been recorded from males placed individually with a female. However, under natural conditions females are exposed to multiple courting males, and the effect of their joint signal on mate recognition by the female is not yet understood. Here, we recorded the courtship behavior of D. melanogaster males singing either individually to a female lpar;1:1) or in the presence of an additional male lpar;2:1). We compared the structure of the male song in the two experimental designs. Our results show that when two males courted a female their songs could overlap each other. Males produced a significantly different signal in the presence of competition; the duration of each song component was significantly shorter and the rate of singing was markedly lower. The present study demonstrates that male competition can dramatically alter the acoustic signal detected by the female.     

Courtship song, male agonistic encounters, and female mate choice in the house cricket,Acheta domesticus (Orthoptera: Gryllidae)

Whether female crickets choose among males based on characteristics of the courtship song is uncertain, but in many species, males not producing courtship song do not mate. In the house cricket,Acheta domesticus, we examined whether a female chose or rejected a male based on his size, latency to chirp, latency to produce courtship song, or rate of the high-frequency pulse of courtship song (“court rate”). We confirmed that females mated only with males that produced courtship song, but we found no evidence that the other factors we measured affected a female’s decision to mate. In addition, we investigated whether the outcome of male agonistic encounters affected the subsequent production of courtship song. In one experiment, we observed courtship and mating behavior when a single female was placed with a pair of males following a 10-min interaction period between the two males. Winners of male agonistic encounters had higher mating success. However, winners and losers of agonistic encounters were not different in their likelihood or latency to produce courtship song or in the number of times they were disrupted by the other male in the pair. In a second experiment, we allowed two males to interact for a 10-min period, but following this interaction period, we placed a female with each male separately and observed courtship and mating behavior. The mating success of winners and losers was not different under these circumstances, and we found no differences between winners and losers in any subsequent courtship or mating behavior examined. We conclude that winning agonistic encounters influences a male’s mating success in ways other than his production of courtship song and this effect is lost when winning and losing males are separated and each is given an opportunity to mate.     

Courtship inDrosophila sechellia: Its structure,functional aspects,and relationship to those of other members of theDrosophila melanogaster species subgroup

The courtship behavior of Drosophila sechelliais described. Male wing displays are mainly vibration and scissoring, with low levels of rowing. As courtship proceeds the proportion of courtship spent in male wing vibration and licking increases, whereas female movement decreases. The male courtship song of sechelliacontains pulse song but no sine song. This species also shows a distinctive copulation song associated with mounting and copulation. The main cuticular hydrocarbon in females is 7,11-heptacosadiene. The number of copulations increased when flies were placed in the presence of food. Visual and acoustic stimuli appear to be important for mating. A multidimensional comparison was used to compare members of the melanogaster species subgroup, based upon courtship behavior, song characteristics, and cuticular hydrocarbons. A multidimensional comparison of courtship sequences in sechellia, melanogaster, simulans,and mauritianashowed differences in variability between the two island species as compared to the two cosmopolitan species. The courtship song of D. orenais described: it shows both sine and pulse song; there is also a copulation song in this species.     

Song preference of female Bengalese finches as measured by operant conditioning

Male songbirds approach females by using their songs. Knowing what females perceive and prefer in male songs is an important aspect of understanding courtship behavior. Male Bengalese finches (Lonchura striata var. domestica) sing complex sequence patterns with their own variety of elements. We tested female preference with phonologically different songs and sequentially different songs using an operant selection task. In the first experiment we presented the father’s song and an unfamiliar song that were phonologically different. Females clearly preferred the father’s song over a novel song. In the second experiment, we used the father’s song and its element order reversed song to test female preference for the difference in element sequence. In the third experiment, we presented different sequence complexity songs edited from the same unfamiliar song elements to test female preference for complex sequence. Females did not show a significant preference in either the second or third experiment. Results show that female Bengalese finches discriminated the difference in song elements, preferred familiar songs, and did not show preference for difference of sequence. This study did not support evidence that female Bengalese finches prefer a complex sequence. However, in future research, we should carefully investigate female preference for choosing mates in a natural context.     

Previous Motor Experience Enhances Courtship Behavior in Male Cricket <Emphasis Type="Italic">Gryllus bimaculatus</Emphasis>

In crickets Gryllus bimaculatus, flight has been shown to be able to promote aggressive encounters between males and to suppress escape behavior. The aim of this study was to examine the influence of flight on male behavior in male–female interactions. We found that flown males demonstrate enhanced courtship behavior. The latency of calling song was significantly shorter, while the relative total duration of singing as well as the duration of singing episodes longer in flown males than in the control. Mating rate was also significantly higher in the experimental group containing flown males. The results suggest that, in addition to previously reported effects on aggressiveness and escape, flying has a profound accelerating effect on male courtship behavior.     

The effect of neurospecific knockdown of candidate genes for locomotor behavior and sound production in Drosophila melanogaster

Molecular mechanisms underlying the functioning of central pattern generators (CPGs) are poorly understood. Investigations using genetic approaches in the model organism Drosophila may help to identify unknown molecular players participating in the formation or control of motor patterns. Here we report Drosophila genes as candidates for involvement in the neural mechanisms responsible for motor functions, such as locomotion and courtship song. Twenty-two Drosophila lines, used for gene identification, were isolated from a previously created collection of 1064 lines, each carrying a P element insertion in one of the autosomes. The lines displayed extreme deviations in locomotor and/or courtship song parameters compared with the whole collection. The behavioral consequences of CNS-specific RNAi-mediated knockdowns for 10 identified genes were estimated. The most prominent changes in the courtship song interpulse interval (IPI) were seen in flies with Sps2 or CG15630 knockdown. Glia-specific knockdown of these genes produced no effect on the IPI. Estrogen-induced knockdown of CG15630 in adults reduced the IPI. The product of the CNS-specific gene, CG15630 (a predicted cell surface receptor), is likely to be directly involved in the functioning of the CPG generating the pulse song pattern. Future studies should ascertain its functional role in the neurons that constitute the song CPG. Other genes (Sps2, CG34460), whose CNS-specific knockdown resulted in IPI reduction, are also worthy of detailed examination.     

Social effects on fruit fly courtship song

Courtship behavior in Drosophila has often been described as a classic innate behavioral repertoire, but more recently extensive plasticity has been described. In particular, prior exposure to acoustic signals of con‐ or heterspecific males can change courtship traits in both sexes that are liable to be important in reproductive isolation. However, it is unknown whether male courtship song itself is socially plastic. We examined courtship song plasticity of two species in the Drosophila melanogaster subgroup. Sexual isolation between the species is influenced by two male song traits, the interpulse interval (IPI) and sinesong frequency (SSF). Neither of these showed plasticity when males had prior experience of con‐ and heterospecific social partners. However, males of both species produced longer bursts of song during courtship when they were exposed to social partners (either con‐ or heterospecific) than when they were reared in isolation. D. melanogaster carrying mutations affecting short‐ or medium‐term memory showed a similar response to the social environment, not supporting a role for learning. Our results demonstrate that the amount of song a male produces during courtship is plastic depending on the social environment, which might reflect the advantage of being able to respond to variation in intrasexual competition, but that song structure itself is relatively inflexible, perhaps due to strong selection against hybridization.     

Broad Selectivity for Courtship Song in the Cricket Gryllus bimaculatus

Various characteristics of a long‐distance acoustic signal have been shown to vary to different degrees. It has been suggested that female preferences based on stable song parameters are stabilising or weakly directional, and preferences based on variable parameters are strongly directional. We tested this hypothesis based on a short‐distance signal (courtship song) produced by the field cricket, Gryllus bimaculatus. We studied the degree of variability of different courtship song parameters and the behavioural importance of several parameters using synthesised song models in playback experiments. We found that most of the courtship song elements of G. bimaculatus were quite variable (coefficient of variation, CV, in the range of 20–53%). The most variable parameter of the courtship song was the relative amplitude of two elements: high‐amplitude ticks and low‐amplitude pulses. Because songs containing only ticks (of rare occurrence) appeared to be more effective than songs with both ticks and pulses (of frequent occurrence), we consider female preferences to be directional. Alteration of less variable traits, such as the carrier frequency and duration of ticks (CV = 20–25%), had a different effect on female responsiveness. The synthesised songs with different carrier frequencies of ticks were as attractive to females as the positive control (courtship of muted males accompanied by playback of the recorded song). Altering the duration of ticks had a crucial effect on the female response rate, decreasing female responsiveness to the level observed in the negative control (courtship of muted males). Thus, we did not find a strong relationship between the variability of individual song parameters and their potential importance in song recognition and the evaluation of male quality. The partial inconsistency of our results with the data of other authors may be due to different patterns of past and current selection on long‐distance and short‐distance acoustic signals.     

Organizing effects of adverse early‐life condition on body mass,compensatory growth and reproduction: experimental studies in rock pigeons

Early‐life food conditions can have profound impact on adult behavioural performance. In song birds, early‐life food conditions affect adult physiology and cognitive performance such as song learning and spatial learning. However, effects on reproductive behaviour other than song, such as visual courtship display, pair formation, and egg laying, which are all important determinants of fitness, received hardly any attention. In this study, rock pigeons Columba livia were raised either in a food ad‐libitum or at impoverished (quality) and restricted (quantity) food conditions, in which the latter was applied for either 26 or 8 d after hatching and in slightly different severity. Their growth and reproductive behaviour in adulthood was analysed under semi‐natural conditions. Impoverished and restricted food (IRF) negatively affected adult body mass, pair‐bonding behaviour, courtship (males) and being courted (females), and induced incomplete compensatory growth. Further analyses suggest that the effects of IRF on behaviour could result from the strong effects on body mass, and perhaps also from detrimental effects of compensatory growth. These results provide evidence that adverse early‐life condition can negatively impact on reproductive success, as suggested by the significant effect on egg production, which will very likely lead to a lower life‐time fitness. The detrimental effects on male courtship indicate that IRF can affect sexual displays via other pathways than by impaired cognition as has been suggested for bird song, since courtship in the pigeons is not learned.     

The behavioural basis of overdominance in competitive mating success at the ebony locus of Drosophila melanogaster

Male files homozygous for the gene ebony¹¹ are partially blind, and at a disadvantage in competitive mating. The courtship of the mutant males is deficient in wing vibration stimulation, which is characterized by a low proportion of sine song and a high intra-pulse frequency. Males heterozygous for ebony have normal vision, but show an increase in courtship song, and are superior in competitive mating to wild type males. The auditory characteristics of courtship song produced by heterozygous males are indistinguishable from those of wild type, and their superiority in competitive mating success is due to overdominance involving this specific element of male courtship behaviour.     

Complex brain and behavioral functions disrupted by mutations in Drosophila

Reproductive behavior in Drosophila involves a complex series of actions which is perturbed by many different kinds of mutations. Some of the most interesting courtship variants are those originally isolated with respect to disruptions of general learning and memory. Several types of genetically abnormal males have their “conditioned courtship” blocked or attenuated by the learning and memory mutations, some of which, in turn, are known to cause abnormal levels of specific monoamines or cyclic nucleotides. Recent studies of the defective courtship performed by the conditioning mutants involve “mosaic focusing” of the neural tissues affected by the behavioral/biochemical mutations. These experiments address the question of whether there are localized influences of the relevant genetic loci in their control of conditioned courtship, in spite of the fact that the protein products of the genes have a broad tissue distribution. Female responses to courting Drosophila males can also be dependent on the former's prior experiences. This pertains to enhancing aftereffects of prestimulation by the courtship song that is produced by a male; and the same learning and memory mutations, expressed in females, impinge on the normal aftereffects. One element of acoustical communication in courtship is a rhythmic oscillation in a particular component of the song. This short-term behavioral rhythm is altered in males expressing circadian rhythm mutations. To investigate the neural and cellular mechanisms by which these genes act, a mosaic analysis has been initiated on the ganglia affected by a clock mutation in its disruption of the courtship rhythm and of circadian cycles. A molecular isolation and identification of the normal form of this genecalled period—has also begun, in order to probe the locus's structure and function in detail. Such an investigation will include a comparison of the mosaic results with a direct determination of the various tissues in which the gene's product is expressed. In addition, interspecific transfers of the purified period gene will augment the current studies of species-specific features of the rhythmic courtship songs.     

Consistency of females’ stridulatory behaviour during inter‐sexual interactions in spiders

In a sexual context, it is expected that females base their choice of mate on the behaviours that males perform during courtship, as such behaviours are associated with the male's mate quality. Stridulation is one form of female communication in arthropods, for example, spiders. In spiders, stridulation during sexual interactions is relatively common in some groups but mainly restricted to males. In the pholcid spider Holocnemus pluchei (Pholcidae), both sexes have stridulatory organs. The aims of the present work were to: (a) determine possible differences in the frequency of occurrence of stridulation between females during inter‐sexual interactions, (b) establish female consistency in stridulation along repeated interactions and (c) analyse if female stridulation is associated with certain male behaviours during pre‐copulatory courtship and with male size. Female H. pluchei showed highly repeatable differences in their frequency of stridulation across consecutive encounters with males (ICC = 0.64). However, only a modest level of repeatability was detected in total time females spent stridulating across trials (ICC = 0.19). Females’ mean stridulatory behaviour did not change across ten consecutive trials spread across 20 days, and their behaviour was apparently unaffected by male persistence of copulatory attempted and/or size. These results imply that the frequency of female stridulatory behaviour is a trait that is highly characteristic of each individual. Finally, our work opens the door to determine whether behavioural consistency manifests in other ecological contexts and their functional implications.     

Signalling and Sexual Conflict: Female Spiders Use Stridulation to Inform Males of Sexual Receptivity

The use of acoustic signals by males during courtship and mating is well known. Nevertheless, their association with female unwillingness to mate is much less studied. In spiders, stridulation during sexual interactions is relatively common in some groups, but mainly restricted to males. In the pholcid spider Holocnemus pluchei, both sexes have stridulatory organs. The aims of the present work were (1) to establish whether female stridulation occurs during intra‐ and inter‐sexual interactions, (2) to determine whether female reproductive status affects the likelihood that she will stridulate and (3) to determine whether female stridulation is influenced by male sexual behaviour. We found that female stridulation usually occurs both during intrasexual interactions and, most frequently, during intersexual interactions. Females with more previous matings stridulated more frequently. Stridulation intensity was higher in females that did not accept new copulations compared with those that copulated. Female stridulation did not vary in elaborated and non‐elaborated courtship. Thus, females use stridulation to communicate levels of sexual receptivity. It is also possible that females use stridulation to indirectly assess male ability to persist and persuade.     

Role of cell death in the formation of sexual dimorphism in the Drosophila central nervous system

Currently, sex differences in behavior are believed to result from sexually dimorphic neural circuits in the central nervous system (CNS). Drosophila melanogaster is a common model organism for studying the relationship between brain structure, behavior, and genes. Recent studies of sex‐specific reproductive behaviors in D. melanogaster have addressed the contribution of sexual differences in the CNS to the control of sex‐specific behaviors and the development of sexual dimorphism. For example, sexually dimorphic regions of the CNS are involved in the initiation of male courtship behavior, the generation of the courtship song, and the induction of male‐specific muscles in D. melanogaster. In this review, I discuss recent findings about the contribution of cell death to the formation of sexually dimorphic neural circuitry and the regulation of sex‐specific cell death by two sex determination factors, Fruitless and Doublesex, in Drosophila.