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     

Function of the Hemolymph Nuptial Gift in the Ground Cricket,Allonemobius socius

Nuptial feeding, although common in the insect world, varies greatly in its form and function. Here, we test the function of the hemolymph nuptial gift in the southern ground cricket, Allonemobius socius, and attempt to determine if it functions as parental investment or mating effort. We manipulated the number of gifts a female received during courtship (one vs. none). We also recorded other aspect of courtship, such as feeding duration and spermatophore attachment duration. Female fecundity was measured for 7 d post‐mating. Our results indicate that female egg laying is significantly higher when a gift is provided, but the increase in egg laying is not related to gift size. In addition, the lack of a gift does not affect the male's ability to transfer a spermatophore. Together, these data suggest that the nuptial gift acts as parental investment and not as mating effort.     

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.     

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.     

Complex Courtship Behavior in the Striped Ground Cricket, Allonemobius socius (Orthoptera: Gryllidae): Does Social Environment Affect Male and Female Behavior?

Complex courtship in the striped ground cricket, Allonemobius socius, involves a series of behaviors alternating between the sexes. We examined if complex courtship allows either or both genders to evaluate their mate and how mating behavior changes in different social environments. While complex courtship may allow discrimination by both sexes, here only females exhibited a preference. Males did not alter their courtship behavior or change spermatophore size for different size females. In contrast, females initiated copulation more quickly with bigger males possessing bigger spermatophores. In a different social environment (additional male, female, or both), males were less likely to omit courtship songs and female discrimination of mates changed. The distinct differences in male and female behavior suggest that subtle changes in social environment can have important consequences in structuring courtship and mating behavior.     

Size-biased Mating in Both Sexes of the Black-horned Tree Cricket, <Emphasis Type="Italic">Oecanthus nigricornis</Emphasis> Walker (Orthoptera: Gryllidae: Oecanthinae)

Previous studies on tree crickets have demonstrated female choice of males based on size and courtship feeding but less is known about sexual selection under conditions of direct mating competition. I studied courtship, aggression and mating of the black-horned tree cricket Oecanthus nigricornis (Walker) to test size-related sexual selection under conditions of direct sexual competition. Results show that larger individuals of both sexes mated more frequently than their smaller counterparts, and this was due to the ability of large individuals to out compete rivals. Large males achieved the advantage by aggressively reducing courtship by small males, whereas large females responded to male courtship more quickly but with little aggression. Although there was no evidence here for mate choice, there were advantages for having larger mates; fecundity increased with female size and spermatophores (which females consume after mating) increased with male size. Size of the specialized metanotal courtship gift, however, was not related to male size.     

Circadian control of spermatophore formation in the cricket Teleogryllus commodus Walker

The cricket Teleogryllus commodus has a circadian rhythm in spermatophore formation. A spermatophore is present 1–5 hr before the onset of stridulation under LL, DD and LD 12 : 12; it is retained during the whole stridulatory phase and disposed of within a variable time after termination of singing. Overwhelmingly one spermatophore is produced during a 24 hr-period. Severance of the abdominal nerve cord or removal of the accessory glands prevent spermatophore formation, but does not inhibit periodical stridulation; when a spermatophore is removed from a singing male, stridulation continues after a short time. Coagulation of the pars intercerebralis stops spermatophore production and singing; severance of the optic lobes rends both processes arhythmical. The rôle of the pars intercerebralis as an intermediary link between the timing-device and the effector organs is discussed.     

The intensity of pre- and post-copulatory mate guarding in relation to spermatophore transfer in the cricket Gryllus bimaculatus

While post-copulatory mate guarding has been well documented in field crickets (Orthoptera: Gryllidae), the occurrence of pre-copulatory mate guarding in this family has been largely overlooked. We examined the relationship between the intensity of two components of mate guarding (body judders and antennal whips) and the time before and after copulation. We found that when male Gryllus bimaculatus encounter a female but do not have a spermatophore ready to transfer, they engage in pre-copulatory mate guarding that is very similar to post-copulatory mate guarding. The intensity of pre-copulatory mate guarding increased up to the point at which the male was ready to transfer his spermatophore. Following copulation, the intensity of mate guarding initially remained high before declining, after which it began to increase again just before the male resumed courtship stridulation. We interpret this pattern of post-copulatory mate guarding as being consistent with both the ejaculate-protection and spermatophore-renewal hypotheses for the function of mate guarding. We found no significant relationship between mate guarding intensity and male body mass.     

Male Gryllus bimaculatus Guard Females to Delay Them from Mating with Rival Males and to Obtain Repeated Copulations

Three hypotheses for the function of postcopulatory mate guarding were tested in the field cricket Gryllus bimaculatus De Geer. The duration of spermatophore attachment was greater in the absence than in the presence of a guarding male. The ejaculate protection hypothesis was, therefore, rejected. The duration of mate guarding was found to be equal to the interval between copulations, supporting the spermatophore renewal hypothesis. In support of the rival exclusion hypothesis, the presence of a guarding male did increase the duration of spermatophore attachment when a rival male was also present. The presence of a guarding male also delayed the female from mating with the rival male. Female mating status had a significant effect on the duration of spermatophore attachment. Females mating for the first time retained the spermatophore for a significantly longer period of time than females that had mated previously.     

Female Choice and the Consistency of Courtship Feeding in Black-horned Tree Crickets Oecanthus nigricornis Walker (Orthoptera: Gryllidae: Oecanthinae)

Courtship feeding in insects is often strongly correlated with insemination duration and therefore provides a potential postcopulatory episode of sexual selection. We tested whether courtship feeding and other courtship traits in the black-horned tree cricket Oecanthus nigricornis showed sufficient consistency potentially to respond to sexual selection by testing whether they differed significantly among males. Duration of courtship feeding differed among males when measured repeatedly and this caused significant differences in the duration of spermatophore attachment, a trait that determines the maximum duration of insemination and thus has important fitness consequences in crickets. We also partitioned variance in courtship behaviour between the sexes to test whether differences in courtship behaviour were attributable primarily to males, females or both sexes. Duration of spermatophore attachment was controlled by females and therefore represents a mechanism of female mate choice. Significant variation in duration of spermatophore attachment was associated with differences between individuals of both sexes. Differences among males indicate that females agree in their preference of certain males whereas differences among females indicate that females differ in their receptivity to postcopulatory courtship and insemination. The fact that differences among males in duration of spermatophore attachment were due to significant differences solely in the period of courtship feeding indicates that postcopulatory female choice was mediated through courtship feeding. Whether males manipulate female choices by allocating more or fewer resources requires further testing, but we found that males court some females more vigorously than others after females dismount. The number of previous mates had opposite effects on the duration of courtship feeding for the sexes, decreasing it for males but increasing it for females, and we discuss the possible causes of these results.     

Mating in the Scaly Cricket Cycloptiloides canariensis (Orthoptera: Gryllidae: Mogoplistinae)

The process of mating in C. canariensis follows basically the same pattern as in other crickets: adoption of the female-above-male position, hooking of the male onto the female's subgenital plate, spermatophore transfer, and separation of the mates. Two crucial modifications can, however, be distinguished: Hooking is not accomplished by means of a sclerotized process from the protruded epiphallus, but with paired hooklets on the paraproct (paraproct processes; sternite 11). The paraproct processes are about 0.4 mm long and covered with bristles, and a group of campaniform sensilla is found in the tip region. The time course of copulation is also modified. Usually, in crickets an already fully formed spermatophore is transferred immediately after mounting, and remains attached for a considerable period. C. canariensis, however, needs about 15 min for spermatophore production, while the couple is already hooked. After transfer the spermatophore remains attached only for an average of 31 s. With both hooklets severed, copulation is unsuccessful. Severance of only one hooklet prolongs the initial hooking phase but shortens the following interval, which suggests that spermatophore production is triggered during a definite interval before hooking, and continues as an autonomous internal process.     

No Effect of Body Size on the Frequency of Calling and Courtship Song in the Two-Spotted Cricket,Gryllus bimaculatus

The relationship between body size and vocalization parameters has been studied in many animal species. In insect species, however, the effect of body size on song frequency has remained unclear. Here we analyzed the effect of body size on the frequency spectra of mating songs produced by the two-spotted cricket, Gryllus bimaculatus. We recorded the calling songs and courtship songs of male crickets of different body sizes. The calling songs contained a frequency component that peaked at 5.7 kHz. On the other hand, courtship songs contained two frequency components that peaked at 5.8 and 14.7 kHz. The dominant frequency of each component in both the calling and courtship songs was constant regardless of body size. The size of the harp and mirror regions in the cricket forewings, which are the acoustic sources of the songs, correlated positively with body size. These findings suggest that the frequency contents of both the calling and courtship songs of the cricket are unaffected by whole body, harp, or mirror size.     

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

We localized brain neurons responsible for the inhibition of copulation actions in the male cricket, Gryllus bimaculatus. Males with one connective-cut between the brain and the terminal abdominal ganglion (TAG) were able to perform normal reproductive behaviors such as courtship, copulation and spermatophore protrusion. However, copulation response tests using a female dummy showed that they failed to exhibit a transient inhibitory state after application of noxious stimulation in the mating stage and to exhibit a tonic inhibitory state in the post-copulatory sexual refractory stage. A partial cut of a single connective (hemilateral connective-cut) combined with the copulation response test and an axonal backfilling demonstrated that approximately 40 brain neurons (per one connective), whose somata were located in the posterior region of the protocerebrum and mainly contralaterally to their descending axons running through the dorso-medial part of the connective, were candidates for the inhibition of copulation actions, at least in the mating stage. In addition, we report here for the first time, that copulation actions can be elicited shortly after copulation even in intact males. This unusual behavior was frequently observed in fledglings after the final molt. The results are discussed from the perspective of the operation of the brain inhibition system on the central pattern generator (CPG) for copulation.     

Sexual signal loss,pleiotropy, and maintenance of a male reproductive polymorphism in crickets

Pleiotropy between male signals and female preferences can facilitate evolution of sexual communication by maintaining coordination between the sexes. Alternatively, it can favor variation in the mating system, such as a reproductive polymorphism. It is unknown how common either of these scenarios is in nature. In Pacific field crickets (Teleogryllus oceanicus) on Kauai, Hawaii, a mutation (flatwing) that segregates as a single locus is responsible for the rapid loss of song production in males. We used outbred cricket colonies fixed for male wing morph to investigate whether homozygous flatwing and normal-wing (wild-type) females differ in responsiveness to male calling song and propensity to mate when paired with either a flatwing or normal-wing male in the presence or absence of courtship song. Flatwing females were less likely to mount a male than normal-wing females. Females of both genotypes showed a preference for normal-wing males and were more likely to mate in the presence of courtship song; normal-wing females were particularly likely to mate with song. Our results show that negative pleiotropy between obligate male silence and female mating behavior can constrain the evolution of sexual signal loss and contribute to the maintenance of a male reproductive polymorphism in the wild.     

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.     

Complex innervation of three neck muscles by motor and dorsal unpaired median neurons in crickets

Summary In the crickets, Gryllus campestris and Gryllus bimaculatus, the innervation of the dorso-ventral neck muscles M62, M57, and M59 was examined using cobalt staining via peripheral nerves and electrophysiological methods. M62 and M57 are each innervated by two motoneurons in the suboesophageal ganglion. The four motoneurons project into the median nerve to bifurcate into the transverse nerves of both sides. M62 and M57 are the only neck muscles innervated via this route. These bifurcating axon-projections are identical to those of the spiracular motoneurons in the prothoracic ganglion innervating the opener and closer muscle of the first thoracic spiracle in the cricket. The morphology of their branching pattern is described. The neck muscle M57 and the opener muscle of the first thoracic spiracle are additionally innervated by one mesothoracic motoneuron each, with similar morphology. These results suggest, that in crickets, the neck muscles M57 and M62 are homologous to spiracular muscles in the thoracic segments. The two neck muscles M62 and M59 (the posterior neighbour of M57) receive projections from a prothoracic dorsal unpaired median (DUM) neuron that also innervates dorsal-longitudinal neck muscles but not M57. In addition, one or two mesothoracic DUM neurons send axon collaterals intersegmentally to M59. This is the first demonstration of the innervation of neck muscles by DUM neurons.     

The effect of remating on sperm number in the spermatophores of Teleogryllus commodus (Gryllidae)

Factors controlling sperm production in members of the Orthoptera have not been fully elucidated. In this study, the influence of intermating interval and ad libidum mating on sperm number was investigated in black field crickets (Teleogryllus commodus). Remating at a variety of time intervals was not characterized by a significant change in sperm number compared with the first mating. Ad libitum mating (i.e., continuous availability of unmated females) had two main effects on spermatophore production and sperm number: first, there was a trend toward increased time between copulations with each successive remating, and second, the number of spermatozoa encapsulated in the transferred spermatophore declined after most rematings, with 61.8% of the initial sperm number being produced for the second spermatophore and 51.3% of the initial sperm number being produced for the third. The decrease in mean sperm number was accompanied by increased variance in sperm number in later rematings. This study suggests that males are willing to suffer a decrease in sperm number if a mating opportunity occurs before the completion of sperm production.     

Courtship Behavior in the Hawaiian Cricket Laupala cerasina: Males Provide Spermless Spermatophores as Nuptial Gifts

The role of sexual selection in the crickets (family Gryllidae) is well known but new forms of courtship behavior continue to be discovered. Here we describe the elaborate mating behavior of the Hawaiian endemic Laupala cerasina (subfamily Trigonidiinae) on the basis of both laboratory and field observations. We found that courtship and mating involve multiple copulations during which repeated spermatophores are transferred. Initial copulations involved the transfer of relatively small ‘microspermatophores’. The final copulation results in the transfer of a considerably larger ‘macrospermatophore’. We tested and rejected the hypothesis that the number of spermatophore transfers results in greater offspring sired by a given male. Matings involving only microspermatophores resulted in no offspring, whereas most matings involving micros and a macrospermatophore, or a macrospermatophore only, produced offspring. A direct examination of the contents of the microspermatophore revealed an absence of sperm, whereas examination of the macrospermatophore revealed the presence of sperm. Given that females consume the spermless microspermatophores, we conclude that the microspermatophores are a form of nuptial feeding of females by males. We discuss possible hypotheses to explain this unusual courtship system.     

No Coolidge Effect in Decorated Crickets

Female decorated crickets, Gryllodes sigillatus , obtain genetic benefits by mating with different males and, when given a choice, prefer novel males over previous mates. It is unknown, however, whether males exhibit a similar preference for novel females. Although female crickets control copulation, there are at least two ways in which males can exercise choice: (1) the amount of courtship directed towards prospective mates and (2) the size of the spermatophore transferred to the female at mating. To determine whether males devote more courtship effort to novel females while controlling for female behavioral cues, male courtship effort toward two dead females, one, a previous mate and the other, a novel female, was measured. To determine whether males manufacture larger spermatophores when paired with novel females, males were mated to novel or previous mates, and the different components of the spermatophore weighed. Males did not spend more time courting dead novel females than previous mates. There was no difference in the latency to remating of males confined with novel females and those paired with previous mates, and there was no difference in the mass of spermatophores transferred to novel and familiar females. Contrary to previous studies in other taxa, this study suggests that male crickets do not prefer novel mates and thus, are not subject to the Coolidge effect. Although mating with novel females may be beneficial to males, selection on males to identify and discriminate against previous mates may be relaxed because of a strong female preference for novel males.