Mate preference for novel partners in the cricket Gryllus bimaculatus

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

New microsatellite loci isolated from the field cricket Gryllus bimaculatus characterized in two cricket species, Gryllus bimaculatus and Gryllus campestris

We have developed a new set of 27 polymorphic markers for each of two cricket species, Gryllus bimaculatus and Gryllus campestris. Initially, 14 published G. bimaculatus loci were tested in G. campestris; however, only five loci were polymorphic. Therefore, we isolated an additional 50 new microsatellite loci from G. bimaculatus and tested these in both species. In a minimum of 20 individuals, 27 of the new loci were polymorphic in G. bimaculatus and 25 in G. campestris.     

Courtship song and immune function in the field cricket Gryllus bimaculatus

It has been assumed that sexual ornaments have evolved to reveal males' health and vigour for females. Choosy females may indirectly use ornaments as an indicator of the presence and effectiveness of genes for resistance against parasites. In this study we tested whether females of the Mediterranean field cricket, Gryllus bimaculatus, can use courtship song as a cue for choosing males with high immunocompetence, measured as encapsulation rate of nylon implants and lytic activity of haemolymph. We found that female crickets preferred courtship songs from males with a high encapsulation rate. Female crickets also had a tendency to prefer courtship songs with high tick rate and long high-frequency tick duration. These preferred song components were positively correlated with encapsulation rate, but negatively correlated with lytic activity of the male. In contrast to previous studies of crickets, there was no correlation between male weight and encapsulation rate or lytic activity. There is some evidence in another cricket species that the ability to encapsulate pathogens is heritable. Thus, in light of this study it seems possible that by preferring males according to their courtship song, females might benefit by increasing the parasite resistance of their offspring.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 79 , 503–510.     

Molecular evidence of post-copulatory inbreeding avoidance in the field cricket Gryllus bimaculatus

Female promiscuity has broad implications for individual behaviour, population genetics and even speciation. In the field cricket Gryllus bimaculatus, females will mate with almost any male presented to them, despite receiving no recorded direct benefits. Previous studies have shown that female crickets can benefit from polyandry through increased hatching success of their eggs. There is evidence that this effect is driven by the potential of polyandrous females to avoid fertilizing eggs with sperm from genetically incompatible males. We provide direct evidence supporting the hypothesis that polyandry is a mechanism to avoid genetic incompatibilities resulting from inbreeding. Using microsatellite markers we examined patterns of paternity in an experiment where each female mated with both a related and an unrelated male in either order. Overall, unrelated males were more successful in gaining paternity than were related males, but this effect was driven by a much greater success of unrelated males when they were the first to mate.     

Behavioral response to antennal tactile stimulation in the field cricket Gryllus bimaculatus

We examined behavioral responses of the field cricket Gryllus bimaculatus to tactile stimuli to the antennae. Three stimulants of similar shape and size but different textures were used: a tibia from the hunting spider Heteropoda venatoria (potential predator), a tibia from the orb-web spider Argiope bruennichi (less likely predator), and a glass rod. Each stimulus session comprised a first gentle contact and a second strong contact. The evoked behavioral responses were classified into four categories: aversion, aggression, antennal search, and no response. Regardless of the stimulants, the crickets exhibited antennal search and aversion most frequently in response to the first and second stimuli, respectively. The frequency of aversion was significantly higher to the tibia of H. venatoria than to other stimulants. The most striking observation was that aggressive responses were exclusive to the H. venatoria tibia. To specify the hair type that induced aggression, we manipulated two types of common hairs (bristle and fine) on the tibia of the predatory spider. When bristle hairs were removed from the H. venatoria tibia, aggression was significantly reduced. These results suggest that antennae can discriminate the tactile texture of external objects and elicit adaptive behavioral responses.     

Female choice in the field cricket Gryllus bimaculatus (De Geer)

Females of the field cricket G. bimaculatus show multiple mating. Since such a strategy is likely to incur costs such as time and energy spent in orientation to calling males or increased susceptibility to predation, it must have certain selective advantages. This study shows that multiple mating is a potential mechanism of mate choice. Females removed the spermatophores of some males before complete insemination was achieved. Females also remained with large males in order to mate a second or third time. Since spermathecal morphology may limit last-male sperm precedence in this species, a function of multiple mating may be to dilute the sperm stored from previous matings with that of the current male, so increasing his representation in offspring production.     

Social isolation increases male aggression toward females in the field cricket Gryllus bimaculatus

Social isolation has often been reported to facilitate male aggressiveness in various animal species. If social isolation also escalates male aggressive behavior towards females, the mating success of the aggressive males will be low. This study evaluated the effect of social isolation on mating behavior in the field cricket Gryllus bimaculatus, which has traditionally been considered to be an asocial species. The results showed that social isolation from same-sex individuals enhanced male aggressiveness to females, and the mating success of aggressive males was reduced under the experimental conditions. More aggressive males exhibited a longer latency to court than less aggressive males. These results suggest that because male aggressiveness causes a delay in courtship, aggressive males may have reduced mating success. This demonstrated that social relationships are a critical factor affecting male mating success, even if the species is normally considered solitary.     

Olfactory memory capacity of the cricket Gryllus bimaculatus

Olfactory learning in insects is a useful model for studying neural mechanisms underlying learning and memory, but memory storage capacity for olfactory learning in insects has not been studied. We investigate whether crickets are capable of simultaneously memorizing seven odour pairs. Fourteen odours were grouped into seven A/B pairs, and crickets in one group were trained to associate A odours with water reward and B odours with saline punishment for all the seven pairs. Crickets in another group were trained with the opposite stimulus arrangement. Crickets in all the groups exhibited significantly greater preference for the odours associated with water reward for all the seven odour pairs. We conclude that crickets are capable of memorizing seven odour pairs at the same time.     

Physics of directional hearing in the cricket Gryllus bimaculatus

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

An empirical test of bet-hedging polyandry hypothesis in the field cricket Gryllus bimaculatus

Journal of Ethology - Theory shows that polyandry (mating with multiple males within a reproductive season) works as bet-hedging to increase the geometric mean fitness (GMF) of polyandrous genotype...     

The flow and fate of digestive enzymes in the field cricket,Gryllus bimaculatus

The flow of enzymes, the ratio of bound to unbound enzymes, and their inactivation in the cricket Gryllus bimaculatus was studied. The digestive enzymes are forced forward into the crop by caecal contraction and then they are mixed with freshly chewed food and saliva, forming a crop‐chyme. This chyme is blended by crop peristalsis, and periodic opening of the preproventricular valve (PPV) allows posterior movement into the proventriculus and further into the midgut. The contraction of the crop is modulated by Grybi‐AST and Grybi‐SK peptides, which are partially secreted by the caecal endocrine cells. Most of the aminopeptidase and the four disaccharidases examined are membrane bound (62–80%); the remaining (20–38%) as well all trypsin, chymotrypsin, lipase, and amylase are secreted free into the caecal lumen. Cricket trypsin loses only 30% of its activity in 4 h and very little thereafter. The presence of digestive products in the lumen appears to retard further trypsin autolysis. Cricket trypsin digests 42% of the chymotrypsin, 37% of the lipase, and 45% of the amylase in the caecal fluids over 24 h in vitro no significant difference. Without Ca ion amylase was almost completely digested. About 50% of the membrane bound and free aminopeptidase was digested in the caecal lumen, and about 30–38% of the bound and free maltase. This loss of digestive enzyme activity is possible, because enzyme secretion rates are high, the unbound enzymes are effectively recycled, and the time of nutrient passage is short.     

Photoperiodic modulation of circadian rhythms in the cricket Gryllus bimaculatus

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

Male size,mating potential and lifetime reproductive success in the field cricket,Gryllus bimaculatus (De Geer)

Male size is known to influence short-term, competitive mating success in the field cricket, Gryllus bimaculatus. Short-term measures of mating success are, however, potentially misleading when considering the influence of sexual selection on male morphology and behaviour. The lifetime mating success of males was investigated in the absence of competition to determine the effects of male size per se on reproductive potential and any effects of female behaviour on male lifetime mating success. The cost of spermatophore production was relatively greater for small males who consequently had a longer refractory period between matings, thus limiting their reproductive potential. Large males had a mating advantage resulting from a differential response of females to the courtship attempts of large and small males. Furthermore, small males were ‘sexually incompetent’ in terms of their ability to attach spermatophores once mounted. There was, therefore, an overall positive relationship between male size and lifetime reproductive success.     

Molecular basis of the dopaminergic system in the cricket Gryllus bimaculatus

In insects, dopamine modulates various aspects of behavior such as learning and memory, arousal and locomotion, and is also a precursor of melanin. To elucidate the molecular basis of the dopaminergic system in the field cricket Gryllus bimaculatus DeGeer, we identified genes involved in dopamine biosynthesis, signal transduction, and dopamine re-uptake in the cricket. Complementary DNA of two isoforms of tyrosine hydroxylase (TH), which convert tyrosine into l-3,4-dihydroxyphenylalanine, was isolated from the cricket brain cDNA library. In addition, four dopamine receptor genes (Dop1, Dop2, Dop3, and DopEcR) and a high-affinity dopamine transporter gene were identified. The two TH isoforms contained isoform-specific regions in the regulatory ACT domain and showed differential expression patterns in different tissues. In addition, the dopamine receptor genes had a receptor subtype-specific distribution: the Dop1, Dop2, and DopEcR genes were broadly expressed in various tissues at differential expression levels, and the Dop3 gene was restrictedly expressed in neuronal tissues and the testicles. Our findings provide a fundamental basis for understanding the dopaminergic regulation of diverse physiological processes in the cricket.     

piggyBac-mediated somatic transformation of the two-spotted cricket, Gryllus bimaculatus

Transgenic insects have been artificially produced to study functions of interesting developmental genes, using insect transposons such as piggyBac. In the case of the cricket, however, transgenic animals have not yet been successfully artificially produced. In the present study, we examined whether the piggyBac transposon functions as a tool for gene delivery in embryos of Gryllus bimaculatus. We used either a piggyBac helper plasmid or a helper RNA synthesized in vitro as a transposase source. An excision assay revealed that the helper RNA was more effective in early Gryllus eggs to transpose a marker gene of eGFP than the helper plasmid containing the piggyBac transposase gene driven by the G. bimaculatus actin3/4 promoter. Further, only when the helper RNA was used, somatic transformation of the embryo with the eGFP gene was observed. These results suggest that the piggyBac system with the helper RNA may be effective for making transgenic crickets.     

Winner and loser effects of juvenile cricket Gryllus bimaculatus

Journal of Ethology - Agonistic encounters of juvenile male crickets were analyzed behaviourally. In a pairing between adult and juvenile male crickets, the juvenile crickets were usually beaten by...     

The precision of auditory lateralization in the cricket, Gryllus bimaculatus

ABSTRACT. The precision of auditory lateralization was determined behaviourally for the cricket, Gryllus bimaculatus L. A forced-choice Y-maze test was devised in which the cricket, on entering the test arena, could not — in contrast to free phonotactic approaches — change its walking direction until after it had passed through a narrow wire-mesh tunnel. For a sound frequency of 4.7 kHz, matching the species' calling frequency, the minimum audible angle for correct side discrimination was 15°. For stimulus angles smaller than 15° from the longitudinal body axis, the crickets walked randomly to either side; stimulus angles greater than 25° resulted in all crickets turning correctly. These data reveal a sharply tuned lateral sensitivity for the auditory pathway of crickets, with an optimum at the species' calling frequency of 4.7 kHz (when compared with 3.5 and 6.0 kHz). The results for the forced-choice test are compared with the walking pattern during free phonotactic approaches, in order to determine the possible strategy underlying the acoustic orientation behaviour of the cricket.     

Correction to: An empirical test of bet-hedging polyandry hypothesis in the field cricket Gryllus bimaculatus

Journal of Ethology -     

Inter-male competition and mating success in the field cricket,Gryllus bimaculatus (de Geer)

Males of the field cricket Gryllus bimaculatus compete aggressively for the acquisition of burrows and females. The effect of population density on the nature of encounters between males, and factors affecting individual competitive ability were examined. Aggression was reduced in high population densities, both in terms of the proportion of encounters leading to aggression and in the intensity of aggressive disputes. The addition of burrows and females increased aggressiveness and removed population density effects. Individual competitive ability was determined primarily by body size and secondly, by an individual's past experience of winning (‘confidence’). Competitive ability, prior residence in burrows and the presence of females all appear to influence the outcome of aggressive disputes. Variation in calling frequency of males was influenced both by population density and competitive ability; males who called more often had a greater encounter rate with females. Females were more likely to mate with burrow residents. However, amongst residents, larger males gained more matings. The potential for female choice in this species is discussed.