Brain control of mating behavior in the male cricket Gryllus bimaculatus DeGeer: the center for inhibition of copulation actions

We re-examined the functional role of the brain and suboesophageal ganglion (SOG) in inhibiting mating behavior in the male cricket Gryllus bimaculatus DeGeer. Experiments were conducted by using mimetic stimulation to elicit copulation actions. To induce a change in the male internal state from a sexually responsive state to a sexually unresponsive state in the mating stage, noxious stimulation, head injury and leg pinching were used. Males that sustained a head injury became sexually unresponsive but became responsive as soon as the brain was removed, while males that underwent the same treatment remained unresponsive after the SOG was destroyed by sectioning. The inhibitory effects of the brain were also demonstrated by the fact that further removal of the SOG in the decerebrated males did not change their copulatory responsiveness, while removal of the brain in SOG-sectioned males markedly increased copulatory responsiveness. Furthermore, decerebrated males did not become sexually unresponsive by leg pinching, while SOG-sectioned males that had recovered sexual responsivenss, did. These results suggest that the brain, and not the SOG, plays a key role in the inhibition of copulation in the male cricket during the mating stage.     

Postembryonic development of mating behavior in the male cricket Gryllus bimaculatus DeGeer

Summary The intact male nymph cricket, Gryllus bimaculatus DeGeer, was found to show mating-like behavior, that is, courtship-like behavior (CSLB) and copulation-like behavior (CPLB), in the 7th and 8th (last) instars. The 8th instar nymph exhibited less CSLB and CPLB than the adult but much more than the 7th instar nymph. The movement patterns of CSLB and CPLB were essentially the same as those of adults except for motor acts requiring the use of the genitalia. CSLB was short and often ceased spontaneously before it switched to CPLB. CPLB also ended earlier than in adults. The occurrence of CSLB and CPLB was almost zero the few days around ecdysis. The nymph was very sensitive to disturbance, so that he often stopped courtship for more than 30 min after stimulation. CSLB was similarly induced in the male nymph (8th instar) by pairing with a female adult, male adult, female nymph (8th) and male nymph (8th). The female nymph (8th) was observed to mount not only the male adult but also the male nymph (8th). A fixed time sexual refractoriness forming a basis of cyclical mating activity was not present after CPLB in the nymph. It appeared in association with the emergence of spermatophore protrusion behavior around day 3 after the imaginal molt. In fledglings, there were some transitions during the sexual maturation process, such as failures in hook hanging, spermatophore extrusion, and spermatophore transfer to the female. The decerebration experiments on nymphs and fresh adults agreed with behavioral observations. These results suggest that the development of mating behavior in the male cricket is a process of enhancement of basic motor patterns but not a process of addition of new movements by changes in pattern generation circuits in the central nervous system.Abbreviations CPLB copulation-like behavior - CPPT interval between copulation and spermatophore protrusion - CSCP interval between calling song and copulation - CSLB courtship-like behavior - CSS courtship song - PTCS interval between spermatophore protrusion and calling song - SPE spermatophore extrusion     

Neurohormonal control of the mating interval in the male cricket,Gryllus bimaculatus DeGeer

Summary Between two mating acts of the male cricket (Gryllus bimaculatus), spermatophore protrusion (SP) and courtship stridulation (CS), there is a fixed time interval. This interval lasts about 1 h. During the period from SP to CS, the male cricket does not stridulate nor make any type of mating sound (post-spermatophore protrusion silence: PSPS) and tolerates external sensory stimuli. We examined the effects of injections of hemolymph and ganglia extracts on the interval. Extracts obtained from crickets which had just started CS (CS crickets) and those which had finished SP (SP crickets) were effective. The extracts were fractionated by ul trafiltration. Fractions with a molecular weight of less than 1 kdalton affected the length of the PSPS. The fractions from both the hemolymph and the mesothoracic ganglion of CS crickets shortened the PSPS. On the other hand, the fractions from the hemolymph and the brain of SP crickets lengthened the PSPS. We estimated, by gel filtration, the molecular weight of the effective fractions from the mesothoracic ganglion and the brain to be 100–200 daltons. We also examined the effects of biogenic amines on the PSPS. Octopamine shortened the PSPS, whereas serotonin lengthened it. The results in dicate that at least two neurohormones from the brain and the mesothoracic ganglion reciprocally control the elicitation of CS and provide an appropriate interval in the mating sequence of the male cricket. Octopamine and serotonin are possible candidates for these neurohormones.Abbreviations CP copulation - CS courtship stridulation - SP spermatophore protrusion - PSPS post-spermatophore protrusion silence     

Distribution and morphology of descending brain neurons in the cricket Gryllus bimaculatus

The number and distribution of descending brain neurons have been investigated in the cricket. The results are based on retrograde labeling of these cells with either Lucifer yellow or Neurobiotin via whole or small split portions of the cervical connectives. Various groups of cells and single neurons have been identified, and the morphology of more than 40 cells is described. Nearly 200 descending brain neurons can be stained via one cervical connective. Their perikarya are concentrated in clusters that occur ipsi- and contralateral to the filled connective and that lie dorsal and ventral in the brain. Descending cells only arborize in the nonglomerular neuropils of the brain and never branch in the optic lobe. Cells descending ipsilaterally never arborize in the contralateral hemisphere, whereas contralateral descending neurons often branch in both hemispheres. Irrespective of soma position, cells can arborize in the ventral and/or dorsal neuropils of the brain. Neurons with somata in the protocerebrum often have branches in the deutocerebrum and vice versa. The main arborizations of the cells from the prominent ventral i5 group are found in the same part of the protocerebrum. In contrast, various cells arborize in the ventral posterior deutocerebrum, but their somata are not located in different clusters. Thus, neurons from the same cluster may, but need not necessarily, arborize in the same brain area.     

Sensory responses of descending brain neurons in the walking cricket, Gryllus bimaculatus

Sensory responses of various descending brain neurons, their modulation during standing or walking, and the correlation of such modulations with stimulus category were investigated. Stimuli involving (1) static or moving grating, artificial calling songs with (2) the conspecific and (3) an ultrasound frequency, or (4) air puffs to the cerci were presented to crickets walking in an open loop paradigm. The morphology of different descending interneurons in the brain and thoracic ganglia is described, together with their respective response properties. Some cells were excited, others inhibited by, and only some were directionally sensitive to the optomotor stimulus. Responses to artificial calling songs with conspecific and ultrasound frequency differed in the way the syllables of the sounds were coded and in the representation of ipsi- and contralateral stimuli. The majority of cells tested responded to air puffs. Stimulus representation differed among individuals of morphological types, but was very similar among individual interneurons of the morphologically homogenous i5 group. Stimuli approximating predators (air puffs, ultrasound) were usually represented during walking and standing; however, most neurons only responded to the other stimuli only during walking. These results indicate that the same neurons show different responses, and may have different functions, under different behavioral conditions.     

Mechanism of execution of sequential motor acts during copulation behavior in the male cricketGryllus bimaculatus DeGeer

Summary The roles of the mechanosensory afferents from the wings, cerci, tergites and genitalia in copulation behavior were examined by ablation and stimulation in the male cricketGryllus bimaculatus DeGeer.The sexually excited male cricket exhibited an intense posture (IP) upon contact stimulation of the elytra and the 4th to 9th abdominal tergites. This posture allowed the backward slipping (BWS) or hooking to take place subsequently.Backward slipping (BWS), which is the movement to get under the female, was elicited during IP by contact stimulation to the middle and distal regions of the dorsal surface of the cercus.Hooking, the coordinated movements for hanging the epiphallus onto the female's subgenital plate could be induced during IP by contact either on the dorsum, periproct or proximal 2 mm regions of the cercus. The latter two regions played a role in performing hooking accurately.Among four types of mechano-sensilla on the cercus the trichoid type was crucial for the initiation of BWS and hooking. Calculations revealed that about 60 trichoid hairs (4% of all the trichoid hairs in one cercus) were sufficient for the male to carry out hooking normally.The input from the bristle hairs on the epiphallus initiated the spermatophore extrusion (SPE) by swelling the endophallus.These results demonstrated that copulation behavior in the male cricket consisted of several motor acts and each act is triggered by specific input from the contact-sensitive sensilla on the elytra, tergites, cerci and genitalia. The sequential execution of each motor act is achieved because one motor act results in a positional change in contact with the female which in turn gives rise to another act. This type of motor control is a model of the so-called chain reaction in instinct behavior.Abbreviations BWS backward slipping - C cercus - EN endophallus - EP epiphallus - EPc epiphallic convexity - FW forewing - H hook - IP intense posture - HW hindwing - P pouch - PP periproct - SP spermatophore - SPE spermatophore extrusion - SEM scanning electron microscope     

Location of the reproductive timer in the male cricket Gryllus bimaculatus DeGeer as revealed by local cooling of the central nervous system

The location of the reproductive timer for the post-copulatory, time-fixed, sexually refractory stage was investigated in the male cricket Gryllus bimaculatus. This stage was defined as the interval between spermatophore protrusion and recommencement of copulation or a calling song. To inactivate the central nervous system locally and reversibly, different body regions were cooled to 10°C for 20-30 min after spermatophore protrusion. A behavioural test then measured the duration of the refractory stage after males recovered from cooling. Males with the head, thorax and anterior abdomen cooled did not show a lengthening of that stage. In contrast, males with the entire abdomen or even the posterior abdominal segments containing only the 6th and terminal (7th-11th) abdominal ganglia showed a lengthening of the refractory stage up to, but not exceeding, the cooling duration. When 20-min cooling was interposed twice after spermatophore protrusion, the refractory stage was lengthened by about 40 min, indicating that interposed cooling did not reset the timer. These results are in agreement with our previous hypothesis that the reproductive timer for the refractory stage in the male cricket is located in the posterior abdominal ganglia, possibly within the terminal abdominal ganglion.     

Location of the reproductive timer in the male cricket Gryllus bimaculatus DeGeer as revealed by local cooling of the central nervous system.

The location of the reproductive timer for the post-copulatory, time-fixed, sexually refractory stage was investigated in the male cricket Gryllus bimaculatus. This stage was defined as the interval between spermatophore protrusion and recommencement of copulation or a calling song. To inactivate the central nervous system locally and reversibly, different body regions were cooled to 10 degrees C for 20-30 min after spermatophore protrusion. A behavioural test then measured the duration of the refractory stage after males recovered from cooling. Males with the head, thorax and anterior abdomen cooled did not show a lengthening of that stage. In contrast, males with the entire abdomen or even the posterior abdominal segments containing only the 6th and terminal (7th-11th) abdominal ganglia showed a lengthening of the refractory stage up to, but not exceeding, the cooling duration. When 20-min cooling was interposed twice after spermatophore protrusion, the refractory stage was lengthened by about 40 min, indicating that interposed cooling did not reset the timer. These results are in agreement with our previous hypothesis that the reproductive timer for the refractory stage in the male cricket is located in the posterior abdominal ganglia, possibly within the terminal abdominal ganglion.     

Cuticular lipids and odors induce sex-specific behaviors in the male cricket Gryllus bimaculatus

Male crickets display sex-specific (e.g., mating and agonistic) behaviors towards conspecific individuals. One of the key signals for these behaviors is the chemical substance on the cricket body surface. In the present study, we analyzed female and male cuticular substances in behavioral assays. Antennal contact stimulation using female forewings elicited a mating behavior in males, while that using male forewings elicited an agonistic behavior in males. Thin-layer-chromatographic and other techniques analysis showed that saturated cuticular lipids were present in both female and male cuticles and that unsaturated lipids were present only in the male cuticle. Filter papers soaked with saturated or unsaturated cuticular lipids were applied to antennae of male crickets. Males showed mating behavior in response to stimulation with saturated lipids from both females and males but showed avoidance behavior in response to stimulation with male unsaturated lipids. Because cuticular lipids did not induce agonistic behavior in males, we collected odors from male crickets and found that these odors induced agonistic behavior in males. Therefore, we concluded that the key signals for mating, avoidance and agonistic behaviors of male crickets are comprised of at least three different components, saturated and unsaturated cuticular lipids and male odors, respectively.     

Two antagonistic functions of neural groups of the femoral chordotonal organ underlie thanatosis in the cricket Gryllus bimaculatus DeGeer

The cricket Gryllus bimaculatus displayed freezing (thanatosis) after struggling while the femoro-tibial joints of the walking legs were forcibly restrained. Myographic recording indicated that strong contraction of the flexor tibia muscle “leg flexion response” occurred under this restrained condition. During thanatosis, when the femoro-tibial joint was passively displaced and held for several seconds, it maintained its new position (catalepsy). Only discharge of the slow flexor units was mechanically indispensable for maintaining thanatosis and catalepsy. Differing roles of identified neuron subgroups of the femoral chordotonal organ were elucidated using this behavioral substrate. Ablation of the dorsal group neurons in the ventral scoloparium strengthened the leg flexion response and the normal resistance reflex, while ablation of the ventral group weakened both motor outputs. Ablation of the dorsal scoloparium neurons, or other main sensory nerves caused no detectable deficiency in femoro-tibial joint control. These results imply that both modes of flexor muscle activation promoted by the ventral group neurons are normally held under inhibitory control by the dorsal group. It is hypothesized that this antagonistic function causes immobilization of the femoro-tibial joint in a wide range of angles in thanatosis and catalepsy. Accepted: 12 November 1998     

Physics of directional hearing in the cricket Gryllus bimaculatus

In the cricket ear, sound acts on the external surface of the tympanum and also reaches the inner surface after travelling in at least three pathways in the tracheal system. We have determined the transmission gain of the three internal sound pathways; that is, the change of amplitude and phase angle from the entrances of the tracheal system to the inner surface of the tympanum. In addition, we have measured the diffraction and time of arrival of sound at the ear and at the three entrances at various directions of sound incidence. By combining these data we have calculated how the total driving force at the tympanum depends on the direction of sound. The results are in reasonable agreement with the directionality of the tympanal vibrations as determined with laser vibrometry.At the frequency of the calling song (4.7 kHz), the direction of the sound has little effect on the amplitudes of the sounds acting on the tympanum, but large effects on their phase angles, especially of the sound waves entering the tracheal system at the contralateral side of the body. The master parameter for causing the directionality of the ear in the forward direction is the sound wave entering the contralateral thoracic spiracle. The phase of this sound component may change by 130–140° with sound direction. The transmission of sound from the contralateral inputs is dominated by a very selective high-pass filter, and large changes in amplitude and phase are seen in the transmitted sounds when the sound frequency changes from 4 to 5 kHz. The directionality is therefore very dependent on sound frequency.The transmission gains vary considerably in different individuals, and much variation was also found in the directional patterns of the ears, especially in the effects of sounds from contralateral directions. However, the directional pattern in the frontal direction is quite robust (at least 5 dB difference between the 330° and 30° directions), so these variations have only little effect on how well the individual animals can approach singing conspecifics.Abbreviations CS contralateral spiracle - CT contralateral tympanum - IS ipsilateral spiracle - IT ipsilateral tympanum - P the vectorial sum of the sounds acting on the tympanum     

Mate preference for novel partners in the cricket Gryllus bimaculatus

Abstract .1. To benefit from the putative genetic advantages of multiple mating with multiple partners, female insects would be expected to select against mating with the same male twice when another potential partner is present.
2. This paper examined whether female Gryllus bimaculatus (Gryllidae) preferred to mate with a novel partner over a partner with which they had mated previously.
3. Females presented with a choice preferred significantly to mate with novel males over previously mated males, and preferred to do so even when the potentially confounding influence of male–male competition was controlled for.
4. The potential advantages of such a mate choice pattern and possible ways in which the choice is mediated are discussed.     

Behaviorally significant immobile state of so-called thanatosis in the cricket Gryllus bimaculatus DeGeer: its characterization, sensory mechanism and function

We have found that the cricket Gryllus bimaculatus shows an immobile posture, so-called thanatosis. Thanatosis was reflexly elicited by gently holding the forelegs and pronotum of the cricket. During thanatosis, the respiration rate decreased markedly while the heart rate doubled compared with the resting state. Animals in the state of extreme rigidity were unresponsive to the external disturbances but easily aroused by mechanical stimulation such as prodding. The immobile posture usually persisted for 2–4 min, but occasionally for more than 20 min, and then suddenly ended. Catalepsy was induced during thanatosis when a leg was passively forced to the extended position. For elicitation of the flexion reflex, either campaniform sensilla and femoral chordotonal organs (FCOs) in the forelegs, and spine-like sensilla on the pronotum were necessary. Among these receptors, however, only the FCOs were involved in inducing the immobile state. Centrally, the brain was indispensable for thanatosis to be maintained. In semi-natural conditions the thanatotic state did occur spontaneously while the cricket struggled to get into a small crevice according to the nature of this species. This sudden immobilization could help the cricket get out of danger of predators like reptiles and amphibians in the natural habitat.Abbreviations FCO femoral chordotonal organ - F-T femorotibial - N nerve     

Escape behavior in response to mechanical stimulation of hindwing in cricket, Gryllus bimaculatus

We studied behavioral responses of the cricket, Gryllus bimaculatus, to mechanical stimulation of the hindwing tip using three different kinds of stimuli: touching, bending and pinching. The most characteristic was a sequence of initial jump-like movements and subsequent running steps, that is referred to as escape behavior in this study. Touching stimulus elicited the escape behavior in 52% of resting animals tethered on a treadmill, whereas bending elicited the same behavior in 94% or 98% depending on the bend direction. Pinching was effective in all tested animals. The effectiveness of pinching stimulus in eliciting the escape behavior depends on the ongoing activity in the animal. Video and electromyographic recordings have revealed that, in the initial jump-like movements, forelegs and hindlegs move simultaneously on both sides while midlegs remain on the ground, followed by simultaneous movements of bilateral midlegs. The subsequent stepping was characterized by out-of-phase rhythmical activities of the leg muscles. Touching stimulus evoked tonic afferent responses of small amplitude in the second nerve root of the metathoracic ganglion. Bending stimulus evoked tonic responses of large units that showed rapid habituation and medium units that persisted during repeated stimulation. Pinching stimulus elicited only phasic responses of large and medium amplitude in the R2 afferents. The results suggest that touching, bending and pinching stimuli are transmitted to the metathoracic ganglion via different sensory systems having different effectiveness in activating the escape motor system.     

Photoperiodic modulation of circadian rhythms in the cricket Gryllus bimaculatus

The waveform and the free-running period of circadian rhythms in constant conditions are often modulated by preceding lighting conditions. We have examined the modulatory effect of variable length of light phase of a 24h light cycle on the ratio of activity (alpha) and rest phase (rho) as well as on the free-running period of the locomotor rhythm in the cricket Gryllus bimaculatus. When experienced the longer light phases, the alpha/rho-ratio was smaller and the free-running period was shorter. The magnitude of changes in alpha/rho-ratio was dependent on the number of cycles exposed, while the free-running period was changed by a single exposure, suggesting that there are separate regulatory mechanisms for the waveform and the free-running period. The neuronal activity of the optic lobe showed the alpha/rho-ratio changing with the preceding photoperiod. When different photoperiodic conditions were given to each of the two optic lobe pacemakers, the alpha/rho-ratio of a single pacemaker was rather intermediate between those of animals treated with either of the two conditions. These results suggest that the storage of the photoperiodic information occurs at least in part in the optic lobe pacemaker, and that the mutual interaction between the bilateral optic lobe pacemakers is involved in the photoperiodic modulation.