Behavioral analyses of wind-evoked escape of the cricket, Gryllodes sigillatus

The wind-evoked escape behavior of the cricket Gryllodes sigillatus was investigated using an air puff stimulus. A high velocity air puff elicited the escape behavior in many crickets. The crickets tended to escape away from the stimulus source, but the direction was not accurately oriented 180 degrees from the stimulus. After bilateral cercal ablation, only a few crickets showed wind-evoked escape behavior, and their response rates did not increase even 19 days after ablation. Therefore, information on air motion detected by cercal filiform hairs is essential for triggering wind-evoked behavior. After unilateral cercal ablation, the 81.3% response rate of intact crickets decreased to 16.5%, that is, it decreased to almost 20% that of intact crickets. One week after unilateral cercal ablation, the response rate recovered to more than 60% that of intact crickets. However, the accuracy rate of the escape direction of G. sigillatus showed no change even immediately after the unilateral cercal ablation. Therefore, both cerci are not necessarily required to determine the escape direction. The behavioral characteristics of wind-evoked escape of G. sigillatus are compared with those of another species of cricket, Gryllus bimaculatus. The two species of cricket employ different strategies for wind-evoked escape.     

Sexually transmitted nematodes affect spermatophylax production in the cricket, Gryllodes sigillatus

Parasites can influence various aspects of host reproductionand mating, including spermatophore production. In the cricket,Gryllodes sigillatus, males transfer to females a two-part spermatophorecontaining a sperm-filled ampulla and a gelatinous spermatophylax(nuptial gift). Here we investigate the effects of a sexuallytransmitted nematode on male spermatophylax production. Sexuallytransmitted diseases (STDs) have the potential to reduce hostfertility or fecundity in insect hosts. To our knowledge thisis the first empirical study on the effects of an insect STDon the reproductive physiology of a male host. Our results indicatethat infected males produced significantly smaller spermatophylacesthan healthy males; this effect was more apparent for smallermales. Spermatophylax size was inversely correlated with theintensity of infection. Spermatophylax replacement time, thetime between producing the first and second spermatophylax,did not differ significantly between infected and healthy males.This parasite-mediated reduction in spermatophylax size maybe a direct consequence of the physiological stress of parasitismor parasite manipulation.     

Mate Guarding in the Cricket Gryllodes sigillatus: Influence of Multiple Potential Partners

There are several hypotheses as to the function of postcopulatory mate guarding. Control over the mate-guarding period by either sex could potentially influence relative reproductive success. Mate-guarding behaviour in Gryllodes sigillatus was studied under several conditions: 1. undisturbed pairs; 2. pairs with a single male intruder; 3. pairs exposed acoustically, visually and olfactorily to several other males; 4. pairs exposed freely to several other males; and 5. pairs exposed freely to several other females. The results provide support for the spermatophore retention and rival defence hypotheses. The efficacy of mate guarding was not compromised by the pair being in acoustic, visual and olfactory contact with several other males. Once pairs were exposed to free contact with several other males, the spermatophore retention time by the female declined significantly, indicating that the mate guarder's efficiency declines under competition from several rivals. In pairs exposed to contact with several females after mating, the mate-guarding period and spermatophore retention time declined as the mate guarder abandoned the mated female and pursued the other females. Termination of the effective mate-guarding period by either sex seems to be influenced by the number of other potential partners present.     

Female Mate Choice, Calling Song and Genetic Variance in the Cricket, Gryllodes sigillatus

Female preferences for song patterns of males of Gryllodes sigillatus and genetic variance of morphological traits correlated with them were analyzed. Females preferred short pulses associated with large males. The males’ thorax width, wing length and femur III length showed stronger relationship with the song pulse duration, whereas the relationship between pulse duration and wing width was not significant. Interestingly, this last trait was the only one that showed significant levels of genetic variance. Perhaps these results could be explained by the evolutionary response to sexual selection. Sexual selection could deplete the genetic variance in the male traits related to male‐mating success.     

Investment in Mate Guarding May Compensate for Constraints on Ejaculate Production in the Cricket Gryllodes sigillatus

Although there is a corpus of evidence that females of many taxa are choosy about males, there is less information on how males may react to females of different 'quality' (i.e. potential fecundity). The cricket Gryllodes sigillatus shows distinct mate guarding behaviour. We examined how long males mate guard females of different sizes (reflecting egg load and potential fecundity). We also examined the sperm number in ampullae donated to females of different sizes to see if males make a concomitant difference in investment in ejaculate. We also examined mate-guarding behaviour and ejaculate size of males mated to virgin and nonvirgin females of the same size to see if males equate size with increased age and increased likelihood of mating (increased sperm competition). The results showed that males mate guard larger females for longer but make no difference in ejaculate investment between sizes of female. Males make no significant difference in mate guarding investment or ejaculate investment between virgins and nonvirgins of the same size. There is evidence that other species of crickets do alter their ejaculate depending on the female size and mating history, but have less distinct guarding behaviour. We suggest that mate-guarding investment in G. sigillatus may serve a similar function to that of ejaculate investment in other crickets.     

Cercal sensory regulation of acetylcholinesterase in nervous system of the cockroach, Periplaneta americana

Cercal ablation caused a significant loss in acetylcholinesterase (AChE) activity of the cercal nerves and terminal ganglion within 12 hr while a similar reduction in enzyme activity of connectives was noticed at least one day after cercectomy. The decrease in AChE activity of the nervous tissues showed a recovery toward control levels from 20 days of unilateral cercectomy whereas the bilateral cercectomy produced a continuous and irreversible decline in enzyme activity. These localized changes in AChE activity of the abdominal nervous system of the cockroach were attributed to be regulated by the cercal sensory innervation.     

Mate Quality and Novelty Influence Post‐Copulatory Female Choice in Decorated Crickets,Gryllodes sigillatus

Females of many taxa prefer to mate with novel males rather than previous mates, but also favor males that have traits indicative of higher genetic quality or compatibility. However, it may not be possible for females to simultaneously choose males that are both novel and of high quality, and the female response to this dilemma has not previously been examined. In this paper, we ask whether female decorated crickets, Gryllodes sigillatus, exert their choice for novel males via post‐copulatory choice (sperm ampulla removal) and whether male genetic background (variation in male quality) affects this decision. We found that after matings with inbred males, females removed the ampullae of familiar mates sooner than those of novel males, whereas after matings with outbred males, there was no difference in the ampulla‐retention times of familiar mates and novel partners. This suggests that when male do not vary in quality, females prefer novel partners. However, when males vary in quality, female preferences for male traits are more important than preferences for novel partners.     

Effects of the Consumption of Male Spermatophylax on the Oviposition Schedule of Females in the Decorated Cricket, Gryllodes sigillatus

The effects of the consumption of the spermatophylax produced by males on female fitness were studied in the decorated cricket, Gryllodes sigillatus. An increase in the number of spermatophylaces presented to females did not increase the total number of eggs made by females, the number of eggs laid, or the hatchability of eggs laid by females, but increased the number of eggs laid in the early stage of adult life of females. The duration of the egg stage decreased with the number of spermatophylaces presented to females. The implication of the results on the sham hypothesis that the spermatophylax does not have nutritional value is discussed.     

Sex-specific genotype-by-environment interactions for cuticular hydrocarbon expression in decorated crickets, Gryllodes sigillatus: implications for the evolution of signal reliability

Phenotypic traits that convey information about individual identity or quality are important in animal social interactions, and the degree to which such traits are influenced by environmental variation can have profound effects on the reliability of these cues. Using inbred genetic lines of the decorated cricket, Gryllodes sigillatus, we manipulated diet quality to test how the cuticular hydrocarbon (CHC) profiles of males and females respond across two different nutritional rearing environments. There were significant differences between lines in the CHC profiles of females, but the effect of diet was not quite statistically significant. There was no significant genotype-by-environment interaction (GEI), suggesting that environmental effects on phenotypic variation in female CHCs are independent of genotype. There was, however, a significant effect of GEI for males, with changes in both signal quantity and content, suggesting that environmental effects on phenotypic expression of male CHCs are dependent on genotype. The differential response of male and female CHC expression to variation in the nutritional environment suggests that these chemical cues may be under sex-specific selection for signal reliability. Female CHCs show the characteristics of reliable cues of identity: high genetic variability, low condition dependence and a high degree of genetic determination. This supports earlier work showing that female CHCs are used in self-recognition to identify previous mates and facilitate polyandry. In contrast, male CHCs show the characteristics of reliable cues of quality: condition dependence and a relatively higher degree of environmental determination. This suggests that male CHCs are likely to function as cues of underlying quality during mate choice and/or male dominance interactions.     

Biogenic amines modulate synaptic transmission between identified giant interneurons and thoracic interneurons in the escape system of the cockroach

In the escape system of the cockroach, Periplaneta americana, a population of uniquely identifiable throacic interneurons (type A or TI_As) receive information about wind via chemical synapses from a population of ventral giant interneurons (vGIs). The TI_As are involved in the integration of sensory information necessary for orienting the animal during escape. It is likely that there are times in an animal's life when it is advantageous to modify the effectiveness of synaptic transmission between the vGIs and the TI_As. Given the central position of the TI_As inthe escape system, this would greatly alter associated motor outputs. We tested the ability of octopamine, serotonin, and dopamine to modulate synaptic transmission between vGIs and TI_As. Both octopamine and dopamine significantly increased the amplitude of vGI-evoked excitatory postsynaptic potentials (EPSPs) in TI_As at 10^?4?10^?2 M, and 10^?3 M, respectively. On the other hand, serotonin significantly decreased the vGI-evoked EPSPs in TI_As at 10^?4?10^?3 M. These results indicate that octopamine, serotonin, and dopamine are capable of modulating the efficacy of transmission of important neural connections within this circuit. © 1992 John Wiley & Sons, Inc.     

Biogenic amines modulate synaptic transmission between identified giant interneurons and thoracic interneurons in the escape system of the cockroach.

In the escape system of the cockroach, Periplaneta americana, a population of uniquely identifiable thoracic interneurons (type A or TIAs) receive information about wind via chemical synapses from a population of ventral giant interneurons (vGIs). The TIAs are involved in the integration of sensory information necessary for orienting the animal during escape. It is likely that there are times in an animal's life when it is advantageous to modify the effectiveness of synaptic transmission between the vGIs and the TIAs. Given the central position of the TIAs in the escape system, this would greatly alter associated motor outputs. We tested the ability of octopamine, serotonin, and dopamine to modulate synaptic transmission between vGIs and TIAs. Both octopamine and dopamine significantly increased the amplitude of vGI-evoked excitatory postsynaptic potentials (EPSPs) in TIAs at 10(-4)-10(-2) M, and 10(-3) M, respectively. On the other hand, serotonin significantly decreased the vGI-evoked EPSPs in TIAs at 10(-4)-10(-3) M. These results indicate that octopamine, serotonin, and dopamine are capable of modulating the efficacy of transmission of important neural connections within this circuit.     

Anatomy and physiology of identified wind-sensitive local interneurons in the cricket cercal sensory system

1. A group of wind sensitive local interneurons (9DL Interneurons) in the terminal abdominal ganglion of the cricket Acheta domesticus were identified and studied using intracellular staining and recording techniques. 2. The 9DL interneurons had apparent resting potentials ranging from -38 mV to -45 mV. At this membrane potential, these cells produced graded responses to wind stimuli; action potentials were never observed at these resting potentials. However, when the 9DL interneurons were hyperpolarized to a membrane potential of approximately -60 mV, a single action potential at the leading edge of the wind stimulus response was sometimes observed. 3. The wind stimulus threshold of the 9DL interneurons to the types of stimuli used in these studies was approximately 0.01 cm/s. Above this threshold, the excitatory responses increased logarithmically with increasing peak wind velocity up to approximately 0.5 cm/s. 4. The 9DL interneurons were directionally sensitive; their response amplitudes varied with wind stimulus orientation. 9DL1 cells responded maximally when stimulated with wind directed at the front of the animal. The apparent peak in directional sensitivity of the 9DL2 interneurons varied between the side and the rear of the animal, depending upon the site of electrode penetration within the cell's dendritic arbor. 5. The locations of dendritic branches of the 9DL interneurons within the afferent map of wind direction were used to predict the excitatory receptive field of these interneurons.     

Morphological, molecular and biological characterization of Mehdinema alii (Nematoda: Diplogasterida) from the decorated cricket (Gryllodes sigillatus)

The nematode Mehdinema alii was recovered from the decorated cricket Gryllodes sigillatus (Walker). Morphometric comparisons are presented from 3 populations. The nematode is characterized by dense arrays of spines on the cuticle of the anterior half of the body and a highly elongate, tubular stoma with a dorsal denticle in the glottoid region. Females have a protruding vulva. Young females are amphidelphic, but the anterior ovary disappears in older females bearing multiple developing juveniles. The male is monorchic with asymmetrically placed genital papillae, distally fused spicules, and a highly complex gubernaculum bearing 2 cuticularized thorns that protrude through a separate, postcloacal opening. Adult nematodes are located primarily in the hindgut, whereas juveniles or dauers occur mainly in the genital chamber of both male and female crickets. Male crickets are significantly more likely to be infected than females. This male-biased infection may be linked to the venereal transmission mechanism of the dauers. Although morphologically unusual in many respects, placement of M. alii in Diplogasterida is supported by both the morphology of the anterior digestive tract as well as analysis of its 18S rDNA sequence. These sequence data suggest that M. alii groups most closely with members of the Cylindrocorporidae.     

Parallel motor pathways from thoracic interneurons of the ventral giant interneurons system of the cockroach,Periplaneta americana

The data described here complete the principal components of the cockroach wind-mediated escape circuit form cercal afferents to leg motor neurons. It was previously known that the cercal afferents excite ventral giant interneurons which then conduct information on wind stimuli to thoracic ganglia. The ventral giant interneurons connect to a large population of interneurons in the thoracic ganglia which, in turn, are capable of exciting motor neurons that control leg movements. Thoracic interneurons that receive constant short latency inputs from ventral giant interneurons have been referred to as type A thoracic interneurons (TI_As). In this paper, we demonstrate that the motor response of TI_As occurs in adjacent ganglia as well as in the ganglion of origin for the TI_A. We then describe the pathway from TI_As to motor neurons in both ganglia. Our observations reveal complex interactions between thoracic interneurons and leg motor neurons. Two parallel pathways exist. TI_As excite leg motor neurons directly and via local interneurons. Latency and amplitude of post-synaptic potentials (PSPs) in motor neurons and local interneurons either in the ganglion of origin or in adjacent ganglia are all similar. However, the sign of the responses recorded in local interneurons (LI) and motor neurons varies according to the TI_A subpopulation based on the location of their cell bodies. One group, the dorsal posterior group, (DPGs) has dorsal cell bodies, whereas the other group, the ventral median cells, (VMC) has ventral cell bodies. All DPG interneurons either excited postsynaptic cells or failed to show any connection at all. In contrast, all VMC interneurons either inhibited postsynaptic cells or failed to show any connection. It appears that the TI_As utilize directional wind information from the ventral giant interneurons to make a decision on the optimal direction of escape. The output connections, which project not only to cells within the ganglion of origin but also to adjacent ganglia and perhaps beyond, could allow this decision to be made throughout the thoracic ganglia as a single unit. However, nothing in these connections indicates a mechanism for making appropriate coordinated leg movements. Because each pair of legs plays a unique role in the turn, this coordination should be controlled by circuits didicated to each leg. We suggest that this is accomplished by local interneurons between TI_As and leg motor neurons.     

Presynaptic effects of biogenic amines modulating synaptic transmission between identified sensory neurons and giant interneurons in the first instar cockroach

Intracellular recording was used to investigate the modulatory effects of serotonin and octopamine on the identified synapses between filiform hair sensory afferents and giant interneurons in the first instar cockroach, Periplaneta americana. Serotonin at 10(-4) mol l(-1) to 10(-3) mol l(-1) reduced the amplitude of the lateral axon-to-ipsilateral giant interneuron 3 excitatory postsynaptic potentials. and octopamine at 10(-4) mol l(-1) increased their amplitude. Similar effects were seen on excitatory postsynaptic potentials in dorsal giant interneuron 6. Several lines of evidence suggest that both substances modulate the amplitude of excitatory postsynaptic potentials by acting presynaptically, rather than on the postsynaptic neuron. The fitting of simple binomial distributions to the postsynaptic potential amplitude histograms suggested that, for both serotonin and octopamine, the number of synaptic release sites was being modulated. Secondly, the amplitudes of miniature excitatory postsynaptic potentials recorded in the presence of tetrodotoxin were unaffected by either modulator. Finally, recordings from contralateral giant interneuron 3, which has two identifiable populations of synaptic inputs, showed that each modulator had a more pronounced effect on excitatory postsynaptic potentials evoked by the lateral axon than on those evoked by the medial axon. Immunocytochemistry confirmed that neuropilar processes containing serotonin are present in close proximity to these synapses.