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.     

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.     

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.     

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.     

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.     

Apolar ecdysteroid esters in adult female crickets, Gryllus bimaculatus

Six hours after injection of 0.5 microCi 3H-ecdysone into the hemocoele of adult female crickets, several labelled compounds could be separated from hemolymph and tissues by silicic acid column chromatography, TLC, and HPLC. The amount of conjugated, polar ecdysteroids was low in all tissues, whereas apolar metabolites were predominant in all tissues. The apolar compound A2, which is the most abundant in quantity, could be hydrolyzed by porcine liver esterase, yielding ecdysone and various long chain fatty acids. This represents a new class of apolar ecdysteroid conjugates not yet found in other insects.     

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.     

Condition-dependent signaling affects male sexual attractiveness in field crickets, Gryllus campestris

The condition dependence of sexually selected traits is an importantassumption of sexual selection theory. Several laboratory studieshave documented a positive relationship between food availability,body condition, and sexual display. However, these studies mightnot reflect the resource allocation between body maintenance,reserves, and the sexually selected trait under natural conditions.Further, the effect of condition-dependent signaling on femalemate choice has hardly been investigated experimentally in thefield. We therefore investigated the effect of food availabilityon body condition, calling behavior, and sexual attractivenessof male field crickets, Gryllus campestris, under field conditions.Food availability was manipulated for individual males by supplementingfood in a confined area close to the burrow. Food-supplementedmales showed a significant increase in body condition, whereasthe opposite was found in the control males. Males receivingextra food called more frequently, whereas the calling-songcharacteristics were not affected by the treatment. Further,food-supplemented males attracted more females than did controlmales, and their higher attractiveness was partly explainedby their superior calling rate. Our study thus indicates condition-dependentsignaling as an important determinant of the sexual attractivenessof males to females under natural condition.     

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.     

Encounter with heavier females changes courtship and fighting efforts of male field crickets Gryllus bimaculatus (Orthoptera: Gryllidae)

The effects of mating experience on male mating behavior are mediated by four factors: mating cost, such as resource depletion, perception of mating opportunities, self-perception of attractiveness, and female quality. For example, encountering females might increase male expectations of prospective mating opportunities, while copulation increases self-perception of attractiveness in males. To determine the relative importance of these factors, the effect of mating on the two components of reproductive effort (courtship and fighting effort) in Gryllus bimaculatus was examined. Calling activity before and after encountering females was measured, and copulation success was recorded. Subsequently, the intensity and outcome of male–male fighting behavior was recorded. Female encounter increased calling activity irrespective of copulation, thereby indicating that the perception of mating opportunities is important factor for the males. Changes in courtship effort of males were larger and fighting success was lower when they were previously paired with relatively heavier females. These results indicate that male reproductive effort is also affected by quality of previous mating partners.

     

Cellular immunosenescence in adult male crickets, Gryllus assimilis

Ecological immunity studies in invertebrates, particularly insects, have generated new insights into trade-offs between immune functions and other physiological parameters. These studies document physiologically directed reallocations of immune costs to other high-cost areas of physiology. Immunosenescence, recognized as the age-related deterioration of immune functions, is another mechanism of radically altering immune systems. We investigated the hypothesis that aging brings on immunosenescence in adult males of the cricket, Gryllus assimilis. Our data show that the intensity of melanotic nodule formation decreased with adult age from after 3-week post-adult emergence. Circulating hemocyte populations similarly decreased from about 5,000 hemocytes/μl hemolymph to about 1,000 hemocytes/μl hemolymph. The numbers of damaged hemocytes in circulation increased from less than 10% at 1-week post-adult emergence to approximately 60% by 3-week post-adult emergence. The composition of hemocyte types changed with age, with increasing proportions of granulocytes and decreasing proportions of plasmatocytes. The declines in nodule formation were not linked to the adult age of sexual behaviors, which begin shortly after entering adulthood in this species. We infer that age-related senescence, rather than cost reallocations, may account for observed declines in various parameters of immune functions in insects, as seen in other animals.     

Behavioral tracing demonstrates dietary nutrient discrimination in two-spotted crickets Gryllus bimaculatus

Animals select appropriate diets to meet their nutritional requirements. Here, we demonstrate the availability for analysis of feeding preference using an orthopteran, the two-spotted cricket Gryllus bimaculatus. A time-course study of these insects, involving continuous recording and tracing behavior for 9 h, allowed us to monitor discrimination of diet that contained various nutrients.     

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.     

Age dependency and tissue distribution of ecdysteroids in adult male crickets,Gryllus bimaculatus de Geer (Ensifera,Gryllidae)

Ecdysteroid titers were determined in tissues (gut plus Malpighian tubules, carcass tissue, fat body, muscles, haemolymph, accessory reproductive glands, and testes) of male adult crickets, Gryllus bimaculatus, during the first 20 days of adult life as well as in spermatophores. In all tissues, except testes, total ecdysteroid titers are high on the day of imaginal moulting and then drop more or less continuously until day 8 after moulting. Distinctly higher levels are found on day 12 and 18 as well. Freshly moulted males contain high quantities of polar ecdysteroid conjugates in the digestive tract, testes, accessory reproductive glands, and haemolymph. Apolar ecdysteroid conjugates are mainly detectable in carcass tissue and fat body, but also in the haemolymph during entire adulthood. Free ecdysteroids represent the domineering class of moulting hormones in the gut during all stages of adult life. The significance of cycling ecdysteroid concentrations during adulthood is discussed in relation to spermatophore production and development of male accessory reproductive glands.     

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.     

Correction to: Encounter with heavier females changes courtship and fighting efforts of male field crickets Gryllus bimaculatus (Orthoptera: Gryllidae)

Journal of Ethology -