Effects of self-generated wind on compensational recovery of escape direction in unilaterally cercus-ablated crickets, Gryllus bimaculatus

The effects of self-generated wind on the compensational recovery of escape direction were investigated in unilaterally cercus-ablated crickets, Gryllus bimaculatus. To separate walking and self-generated wind during walking, unilaterally cercus-ablated crickets were placed on a styrofoam ball that was easily rotated by leg motion during walking. The stationary walking on the ball did not produce self-generated wind, because no body motion occurred. Crickets that were trained on the ball but given no artificial air puff for 14 days after cercal ablation did not show any compensational recovery of escape direction. Therefore, spontaneous walking itself was not sufficient to compensate the wind-evoked escape direction in the crickets. Artificial air puffs from the anterior direction synchronized with the stationary walking were effective for the compensational recovery of escape direction, but those from the posterior direction were not. As most of the spontaneous walking was directed to the forward direction, only an artificial air puff from the anterior direction coincided well with actual self-generated wind occurring during the onset of normal walking. Therefore, self-generated wind during walking seems essential for the compensational recovery of escape direction in unilaterally cercus-ablated crickets. When artificial air puffs were unsynchronized with walking, no compensational recovery was observed. This result suggests that artificial air puffs should be given just after the onset of spontaneous walking. Otherwise, the artificial air puffs may not be recognized as self-generated wind.     

Rearing under different conditions results in different functional recoveries of giant interneurons in unilaterally cercus-ablated crickets, Gryllus bimaculatus

The effects of rearing conditions on the functional recovery of wind-sensitive giant interneurons (GIs) after unilateral cercal ablation were investigated in the cricket, Gryllus bimaculatus. Crickets were reared in a glass vials to prohibit free walking for 14 days after unilateral cercal ablation ("14-day vial" crickets). Other crickets were reared in an apparatus called a "walking inducer" (WI) to increase the walking distance during the same 14-day period ("14-day WI" crickets). In these crickets, the response properties of GIs 8-1, 9-1, 9-2, and 9-3 to air currents from various directions were investigated. From the intensity-response curves obtained, directionality curves expressed in terms of threshold velocity and response magnitude were made independently. To understand changes in the functional recovery of GIs more thoroughly, the directional characteristics of GIs in crickets 1 day after unilateral cercal ablation ("1-day free" crickets) were also compared. Between the 1-day free and 14-day vial crickets, all the GIs showed differences in both threshold velocity and response magnitude for some stimulus directions. Between the 14-day vial and 14-day WI crickets, differences in the threshold velocities of GIs 9-1, 9-2, and 9-3, and in the response magnitudes of GIs 8-1, 9-1, and 9-3 were detected. Because the rearing condition after unilateral cercal ablation largely affects the compensatory recovery in some parameters of wind-evoked escape behavior, such as relative occurrence and escape direction, we discuss the functional differences in GIs revealed here in relation to the roles of GIs in the neural system that controls escape behavior.     

Sensitive period in which walking affects recovery of direction of wind-evoked escape in the cricket Gryllus bimaculatus

Unilaterally cercus-ablated crickets, Gryllus bimaculatus, were reared in an apparatus that induced walking artificially. In the crickets that experienced different distances of enforced walking per day, the directionality of escape was investigated before and 1, 4, 7, 10, 13, and 16 days after the ablation of the cercus. The crickets that walked a longer distance per day showed a quicker and a higher degree of compensational recovery of the escape direction than the crickets that walked a shorter distance per day, even after walking the same distance. Thus, the time course and amount of compensational recovery from cercal ablation depend on when crickets experience walking during the recovery period. During the recovery period, unilaterally cercus-ablated crickets were subjected to walking at different times to determine the most effective period in which walking affects the compensational recovery of escape direction. The compensational recovery of the escape direction occurred only in crickets experiencing walking in early periods after the ablation. In particular, walking experienced 2-6 days after the ablation was most effective for the compensational recovery. On the other hand, no compensational recovery occurred in crickets experiencing walking in later periods after the ablation. These results suggest that there is a sensitive or critical period in which walking affects the compensational recovery of escape direction.     

Ecdysone metabolism in adult crickets,Gryllus bimaculatus

The fate of injected [³H]ecdysone has been investigated in female and male adults of the Mediterranean field cricket, Gryllus binaculatus (de Geer). The metabolism is similar in both sexes and at various stages of adult life. Several classes of apolar metabolites (A1–A5) represent the major compounds. The amount of polar conjugates is low in all tissues, as are the concentrations of 20-hydroxyecdysone. Ovaries are the only organs capable of storing considerable amounts of ecdysteroids. The amount of radiolabelled ecdysteroid activity (mostly [³H]ecdysone) excreted during the first 24 hr after injection is high.The chemical identity of the apolar metabolites is not yet known. A2, which is the major apolar compound, has recently been identified as a complex of ecdysone conjugates with abundant long-chain fatty acids (Hoffman et al., 1985 Life Sci.37, 185–192). Incubations with tissue homogenates in vitro have shown that several organs are capable of converting ecdysone into apolar compounds. Apolar ecdysteroid acyl esters represent a newly identified class of ecdysone conjugates from insects. Their role in regulation of free ecdysteroid titres during the reproductive period in female crickets is discussed.     

Experience-based agonistic behavior in female crickets, Gryllus bimaculatus

Fighting behavior in male crickets is already well described, and some of the mechanisms underlying aggression and aggressive motivation have already been revealed. Much less is known about female/female interactions. Here, we report that adult female crickets that had been isolated for several days readily entered into agonistic interactions with conspecific individuals. Characteristic dyadic encounters between isolated females escalated in a stepwise manner and were concluded with the establishment of a dominant/subordinate relationship. For 15 to 30 minutes following an initial fight, former subordinate females showed a dramatic change in agonistic behavior. If they were paired with the former dominant opponent during this interval, a significant majority did not enter into any aggressive interaction but instead actively avoided the opponent. A similar experience-based and time-dependent increase in avoidance was observed when former subordinate females were paired with unfamiliar na?ve opponents. However, when faced with an unfamiliar subordinate individual in the second encounter, no such increase in avoidance behavior was observed. We propose that the observed changes in the behavior of former subordinate females are the consequence of a change in the general state of arousal and of the recognition of dominance status, but not of individual recognition. The fact that former dominant individuals did not show similar experience-based changes in agonistic behavior suggests that dominant/subordinate relationships between pairs of female crickets are maintained mainly by the behavior of subordinate individuals.     

Free ecdysteroids in adult male crickets, Gryllus bimaculatus

ABSTRACT. Ecdysteroid titres were determined in testes, fat body, muscles, haemolymph, carcass tissue, spermatophores, and faeces of males of the Mediterranean field cricket, Gryllus bimaculatus de Geer, throughout its adult life span. Considerable amounts of free ecdysteroids are concentrated in the testes and the fat body. The ecdysteroid titres were only slightly influenced by environmental temperature. In all tissues except the fat body, ecdysone and 20-hydroxyecdysone were the predominant ecdysteroids present. In faeces, highest ecdysteroid concentrations were found at the time of lowest levels in tissues.     

Aggressive behavior of the white-eye mutant crickets, Gryllus bimaculatus

Aggressive behavior of white-eye mutant crickets was investigated and compared with that of wild-type crickets. In the dark, wild-type pairs performed long-lasting fights with significantly higher aggressive levels compared to those in the light. In contrast, fights between two white-eye mutants were not significantly different with those between two wild-type crickets both in duration and the aggressive levels. Ethograms of aggressive behavior showed that the mutants could show typical sequentially escalating fight with the same behavioral categories as the wild-type crickets. These results indicate that the white-eye mutants are able to express normal aggressive behavior.     

Changes in the biochemical composition of fat body stores during adult development of female crickets, Gryllus bimaculatus

Age-dependent changes in the fat body composition and aspects of lipogenesis in the free abdominal fat body of female crickets, Gryllus bimaculatus, were studied. Lipid, protein, glycogen, and free carbohydrate content of the fat body, and fat body wet weight increased simultaneously and sharply from day 0 onwards and were doubled/almost doubled by day 2 after adult emergence. Lipogenic activity of the fat body, fat body weight, and the energy stores in the fat body peaked on day 2, except for free carbohydrate, which peaked on day 3. On day 2, the fat body was mainly comprised of lipid (53.8%) and protein (6.6%), while glycogen and free carbohydrate together contributed less than 1% of the fat body wet weight. After peaking, both lipogenesis and energy stores decreased in a synchronous manner. The depletion of the fat body energy stores and the consequent decrease in the fat body weight were concomitant with a fast and massive gain in ovary weight (day 2: 19.5 +/- 1.5 mg; day 4: 332.8 +/- 31.5 mg) due to the vitellogenic oocyte growth that started on day 2. Our data clearly underline the importance of the free abdominal fat body as a source of energy for reproduction in the cricket. Fat body fatty acid synthase activity coincided with lipogenic activity. Adipokinetic hormone inhibits lipid synthesis in the fat body, but treatment of the fat body with adipokinetic hormone in vitro showed no consistent effect on fatty acid synthase activity.     

Effects of previous experience on the agonistic behaviour of male crickets, Gryllus bimaculatus

Male solitary animals frequently enter aggressive interactions with conspecific individuals to protect their territory or to gain access to females. After an agonistic encounter, the loser (subordinate individual) changes its behaviour from aggression to avoidance. We investigated agonistic interactions between pairs of male crickets to understand how dominance is established and maintained. Two na?ve males readily entered into agonistic interactions. Fights escalated in a stereotyped manner and were concluded with the establishment of dominance. If individuals were isolated after the first encounter and placed together 15 minutes later, subordinate crickets tended to avoid any further contact with the former dominant opponent. Moreover, subordinate males also avoided unfamiliar dominant and na?ve opponents. They displayed aggressive behaviour only towards unfamiliar subordinate opponents. This suggests that the subordinate male change their behaviour depending on the dominance status of the opponent. Dominant crickets, in contrast, displayed aggressive behaviour towards familiar as well as unfamiliar opponents. If the interval between the first and second encounter was longer than 30 minutes, the former subordinate male showed aggressive behaviour again. However, if the subordinate cricket was paired with the same opponent three consecutive times within 45 minutes, it avoided the former dominant opponent for up to 6 hours following the third encounter. Our results suggest that the maintenance of dominance in male crickets depends largely on the behavioural change of subordinate individuals. Possible mechanisms to maintain dominance are discussed.     

In vivo effects of allatostatins in crickets,Gryllus bimaculatus (Ensifera: Gryllidae)

Two types of cricket allatostatins, Grb-AST A1 and Grb-AST B1, were injected into adult female crickets three times each day on days 0–3 and once on day 4 after adult emergence to test their activity in vivo. On day 4, body weight, ovary weight, number of eggs per ovary, length of the terminal oocytes, ovarian ecdysteroid biosynthesis, and hemolymph titers of ecdysteroids were lower in the allatostatin-injected animals compared with untreated and Ringer-injected controls. Effects of the injected allatostatins on hemolymph juvenile hormone titers were inhomogeneous, and no differences were found in the capacity of the corpora allata to produce juvenile hormone ex vivo. The hemolymph titers of yolk proteins (vitellogenins) were almost twice as high in the allatostatin-injected animals as in the control animals. The effects of the injected allatostatins and their interactions with the endocrine system of the animal are discussed. Arch. Insect Biochem. Physiol. 38:32– 43, 1998. © 1998 Wiley-Liss, Inc.     

Effects of NO/cGMP signaling on behavioral changes in subordinate male crickets, Gryllus bimaculatus

After a loss against an opponent, the aggressiveness of a male cricket is significantly reduced for up to 30 minutes. This depression of aggressiveness is an important factor in the establishment and maintenance of dominance between individuals. In the present study, we investigated the functional roles of nitric oxide (NO) signaling in the depression of aggressiveness in subordinate male crickets. Pairs of male crickets, pre-injected with various NO-related reagents, were allowed to establish dominant/subordinate relationships in dyadic encounters. Opponents were separated for 15 minutes and then paired again. In second encounters, subordinate crickets pre-injected with PTIO (NO scavenger) showed agonistic behavior towards former dominant opponents. A similar effect was observed in crickets pre-injected with L-NAME (NO synthase inhibitor) or ODQ (soluble guanylate cyclase inhibitor). The effects of the latter two drugs were canceled by co-injection of NOR3 (NO donor) with L-NAME or by co-injection of 8-Br-cGMP (cGMP-analog) with ODQ. Injection of NOR3 alone prolonged the inhibition of agonistic behavior in subordinate crickets from 30 minutes to 3 hours. Our results suggest that the change in agonistic behavior observed in subordinate male crickets is closely linked to NO-mediated cGMP signaling.     

Effects of aggression and wing removal on brain serotonin levels in male crickets,Gryllus bimaculatus

When pairs of adult male crickets (Gryllus bimaculatus) that had been housed individually for 7 days were placed together, they fought, and dominant-subordinate relationships were formed within 1min. Aggressive behavior by the dominant male was repeated during the period in which the two males were kept together. Immediately after 10min of aggressive interaction, brain serotonin (5-hydroxytryptamine, 5-HT) levels were unchanged in dominant males and significantly reduced in subordinate males. The emission of aggressive song by dominant males is known to be abolished by removal of the wings. All wings were thus removed from male crickets. After 7 days of isolation, pairs of wingless males were placed together. The wingless males fought and formed dominant-subordinate relationships within 1min. The wingless, dominant males displayed aggressive behavior. Brain 5-HT levels in the wingless males were reduced immediately after 10min of aggressive interaction, and no significant differences in brain 5-HT levels were detected between the dominant and subordinate males, unlike the case for intact males. These data indicate a difference in brain serotonergic activity between dominant and subordinate male crickets during aggressive interaction, and suggest that aggressive behavior by dominant male crickets rapidly reduce brain 5-HT levels in subordinate ones. Furthermore, the data suggest that aggressive song is responsible for the change in brain 5-HT levels.     

Serotonin precursor (5-hydroxytryptophan) causes substantial changes in the fighting behavior of male crickets, Gryllus bimaculatus

This study demonstrates that injection of the serotonin precursor 5-HTP causes substantial changes in the behavioral state, fighting behavior and ability to establish winner–loser relationships in male crickets (Gryllus bimaculatus). The characteristic features of 5-HTP-treated crickets include an elevated posture, enhanced general activity, longer duration of fighting, enhanced rival singing and a decreased ability to produce a clear fight loser. In addition, 5-HTP-treated males showed a slightly delayed latency to spread their mandibles, a decreased number of attacks and an equal potential to win in comparison to controls (physiological solution-treated males). The obtained results imply a significant role for serotonin in the regulation of social status-related behaviors in G. bimaculatus. Specifically, these data indicate that a decrease in serotonergic activity may be functionally important for the control of loser behavior and that some behavioral features of dominant male crickets are likely to be connected with the activation of the serotonergic system.     

Courtship and copulation, but not ejaculates, reduce the longevity of female field crickets (Gryllus bimaculatus)

Females of many taxa incur fitness costs from male sexual coercion and harassment leading to mating. Although male crickets cannot force copulations on females, female Gryllus bimaculatus in this study incurred significant reductions in longevity through being exposed to different levels of male courtship. Virgin females kept in isolation had the longest life spans. Reductions in longevity applied to females in sensory contact with males (without the opportunity to mate), females that courted and mated and females that mated but with fertilization being prevented. Females also incurred significant reductions in longevity when kept with other females, which may have been due to high levels of cannibalism. Consistent with previous studies, females appeared to incur no cost to longevity from receiving sperm or seminal fluid. It is known that female G. bimaculatus benefit genetically from multiple mating. However, this benefit could possibly be offset by the negative effect that male courtship and mating behaviour has on female longevity.     

Protein deprivation decreases male survival and the intensity of sexual antagonism in southern field crickets Gryllus bimaculatus

Recent theory predicts that the magnitude of sexual antagonism should depend on how well populations are adapted to their environment. We tested this idea experimentally by comparing intersexual genetic correlations for adult survival in pedigreed populations of southern field crickets (Gryllus bimaculatus) raised on naturally balanced (free‐choice) vs. imbalanced (protein‐deprived) diets. We tested for (1) sex differences in nutritional intake and preference, (2) sex‐specific effects of protein deprivation on survival and (3) diet dependence of the level of sexual antagonism. Adult males and females consumed a similar amount of protein, but protein deprivation decreased male survival but not female survival. Protein deprivation appeared to decrease the degree of sexual antagonism as intersexual genetic correlations were significantly lower than 1 only for the complementary free‐choice diet group but close to 1 for the protein‐deficient diet group. Our findings thereby implied that variation in nutritional environments can alter the magnitude of sexual antagonism. This research represents an important step towards understanding the relationship between sexual antagonism and adaptation in heterogeneous environments.     

Effects of a daily temperature cycle on ecdysteroid and cyclic nucleotide titres in adult female crickets, Gryllus bimaculatus

ABSTRACT. Ecdysteroid and cyclic nucleotide titres were determined in ovaries, fat body, muscles, haemolymph and the remaining carcass tissue (cyclic nucleotides only in ovaries and fat body) of females of the Mediterranean field cricket, Gryllus bimaculatus de Geer, during its adult life span. Under a daily temperature cycle 24°: 12°C (16:8h), ecdysteroid levels of the ovaries and fat body reached maximal values 5 times as great and about 10 days earlier than they did under constant 20°C. Under both temperature regimes the highest ecdysone concentrations coincided with the maximum in ovarian fresh weight as well as with the maximum oviposition rate. In the ovaries, titres of c-AMP and c-GMP changed roughly in parallel, the levels of c-GMP, however, were much lower than those of c-AMP. A comparison of the cyclic nucleotide profiles in the ovaries with the ecdysteroid profile shows that the cyclic nucleotide concentrations increase when ecdysteroid titres are still low, and that the highest cyclic nucleotide levels were reached 6–12 days earlier than the highest ecdysteroid titres.     

Haemolymph juvenile hormone III esterase activity during adult life of female and male crickets,Gryllus bimaculatus de Geer (Ensifera,Gryllidae)

Using an in vitro method, juvenile hormone III degradation was studied in the plasma of adult female and male crickets, Gryllus bimaculatus. The primary route of juvenile hormone III metabolism in cricket haemolymph is ester hydrolysis to juvenile hormone III acid by juvenile hormone III esterase. Juvenile hormone III esterase activity in females' haemolymph is low just after imaginal moulting. A sharp peak of enzyme activity is observed on day 3 after emergence, and two subsequent peak values occur in older animals. Plasma juvenile hormone III esterase activity in freshly ecdysed males is also low, but increases rapidly thereafter. Another increase in enzyme activity is observed in older males. The fluctuations in juvenile hormone III esterase activity are discussed in correlation with changes in haemolymph volume, haemolymph protein content, haemolymph juvenile hormone III titer, and the rates of juvenile hormone III biosynthesis in vitro of the corpora allata.