Calls of Recently Introduced Coquí Frogs Do Not Interfere with Cricket Phonotaxis in Hawaii

Acoustically-signaling animals such as crickets may experience interference from environmental noise, a particular concern given the rise in anthropogenic or other novel sources of sound. We examined the potential for acoustic interference of female phonotaxis to calling song in the Pacific field cricket (Teleogryllus oceanicus) by invasive coqui frogs (Eleutherodactylus coqui) in Hawaii. The frogs were introduced to Hawaii from Puerto Rico in the 1980s. When female crickets were exposed to male calling songs with and without simultaneous broadcast of a coqui chorus, they were equally likely to move toward the cricket song, regardless of the location of the frog sound (ground level or above ground). Unlike some species of frogs and birds, T. oceanicus do not appear to experience acoustic interference from an introduced signaler, even though the introduced species’ calls subjectively seem to be masking the crickets’ songs.     

Sex,death, and genetic variation: natural and sexual selection on cricket song

Male field crickets, Gryllus integer, in Texas, USA, produce a trilled calling song that attracts female crickets, resulting in enhanced mating success. Gravid female parasitoid flies, Ormia ochracea, are also attracted to male cricket calling song, resulting in the death of the male within about seven days. Using playbacks of field-cricket calling song in the natural habitat, we show that both female crickets and female parasitoid flies prefer male calling song with average numbers of pulses per trill. Thus female crickets exert stabilizing sexual selection, whereas flies exert disruptive natural selection on male song. Disruptive natural selection will promote genetic variation and population divergence. Stabilizing sexual selection will reduce genetic variation and maintain population cohesiveness. These forces may balance and together maintain the observed high levels of genetic variation (ca. 40%) in male calling song.     

In situ measurement of calling metabolic rate in an Australian mole cricket, Gryllotalpa monanka

Examination of the energetics of sound production usually requires measurement of species that will produce normal calls under unnatural circumstances. Such measurements are potentially compromised by stress-related changes in calling input (through a reduction in calling effort) or output (through forced use of sub-optimal singing burrows). To determine if such measurements are indeed affected by abstraction from a natural setting, we measured the energetics of song production in undisturbed mole crickets Gryllotalpa monanka and employed a new approach where the animal's singing chamber replaces the respirometry chamber normally used in studies of this type. It was therefore possible to measure metabolic rate (MR) of calling crickets in situ for animals within self-constructed burrows under natural conditions. Calling MR measured under these conditions averaged 13.5-fold higher than standard MR and 2.2-fold higher than MR measured during burrowing in the lab. The calling MR of G. monanka was similar to that measured for other calling insects, and to endothermic insects, but was only 10% of that allometrically predicted for a similarly sized insect (0.89 g) during flight. A male mole cricket is estimated to consume 5.9 ml of oxygen during construction of a calling burrow and a 1-h calling bout; by comparison, a flying female would consume a similar volume in less than 6 min.     

In situ measurement of calling metabolic rate in an Australian mole cricket, Gryllotalpa monanka.

Examination of the energetics of sound production usually requires measurement of species that will produce normal calls under unnatural circumstances. Such measurements are potentially compromised by stress-related changes in calling input (through a reduction in calling effort) or output (through forced use of sub-optimal singing burrows). To determine if such measurements are indeed affected by abstraction from a natural setting, we measured the energetics of song production in undisturbed mole crickets Gryllotalpa monanka and employed a new approach where the animal's singing chamber replaces the respirometry chamber normally used in studies of this type. It was therefore possible to measure metabolic rate (MR) of calling crickets in situ for animals within self-constructed burrows under natural conditions. Calling MR measured under these conditions averaged 13.5-fold higher than standard MR and 2.2-fold higher than MR measured during burrowing in the lab. The calling MR of G. monanka was similar to that measured for other calling insects, and to endothermic insects, but was only 10% of that allometrically predicted for a similarly sized insect (0.89 g) during flight. A male mole cricket is estimated to consume 5.9 ml of oxygen during construction of a calling burrow and a 1-h calling bout; by comparison, a flying female would consume a similar volume in less than 6 min.     

Seasonal Variation in Female Response to Male Calling Song in the Field Cricket, Gryllus rubens

Conspicuous traits that make males attractive to females may make them vulnerable to predators. Females that approach conspicuous males may increase their risk of predation. This means that selection for reduced male conspicuousness in the presence of predators may be due to sexual selection resulting from altered female behavior in the face of increased predator risk. We examine this hypothesis in the field cricket, Gryllus rubens, in which male calling song attracts both conspecific females for mating and parasitoid flies (Ormia ochracea) which kill their hosts within a week. Female crickets are also parasitized by these flies as a result of associating with calling males. In northern Florida crickets that emerge in the spring are not subject to fly parasitism whereas autumn crickets encounter large numbers of flies. We predicted that autumn females should be less attracted to male song than spring females. We tested female response to male calls in a rectangular arena in which male calling song was broadcast from a speaker. Spring females readily approached the speaker but autumn females were less likely to approach and remain in the vicinity of the speaker. These results emphasize the importance of considering how risk affects the evolution of conspicuous male behavior both directly through its effect on the male and indirectly through its effect on female responses to males.     

The calling song of the field cricket,Gryllus bimaculatus (de geer): constraints on transmission and its role in intermale competition and female choice

Field studies of calling male field crickets, Gryllus bimaculatus, showed that males formed calling aggregations. Within aggregations males appeared to maintain an exclusive female-attraction zone about their burrows; calling song may thus serve as an aggressive signal to neighbouring males to maintain spacing. Calling song attenuates with distance. Furthermore, calls became degraded with distance by the loss of low frequency components and a reduction in the interval between chirps and pulses due to reverberation. Playback experiments suggested that the predictable degrading properties of the call may serve as a distance-finding mechanism maintaining observed male spacing. The intensity of calls and the repetition rate of chirps and pulses was positively correlated with male size. While information contained within the intensity parameter of calls may prove unreliable due to unpredictable attenuation and irregular amplitude fluctuations, the repetition rate of chirps and pulses was not affected by distance degradation. Playback experiments in which intensity was controlled suggested that females orientate preferentially to the calls of large males.     

Males make poor meals: a comparison of nutrient extraction during sexual cannibalism and predation

Cannibalism is hypothesized to have evolved as a way to obtain a high-quality meal. We examined the extraction of lipid and protein by female wolf spiders, Hogna helluo, during sexual cannibalism of males and predation of crickets. Most food-limited females did not cannibalize males but immediately consumed a size-matched cricket. When consuming male H. helluo and crickets, female H. helluo only consumed 51% of the male body while they consumed 72% of the cricket body. While males had higher protein content in their bodies than crickets and other insects, female H. helluo ingested similar amounts of protein from male H. helluo and crickets. Female H. helluo extracted 47% of the protein present in male H. helluo and 67% of the protein present in crickets. Females were able to extract nearly all of the lipid present in male H. helluo and crickets. However, crickets and other insects had almost 4 times higher lipid content than male H. helluo. The ratio of lipid to protein consumed from crickets appeared more similar to the nutritional requirements of egg production than that of males. Taken together, female hesitancy to engage in cannibalism, low extraction of nutrients from males and a low ratio of lipid to protein in the food extracted from males suggest that males may be poor-quality prey items compared to common insects such as crickets.     

Gleaning bat echolocation calls do not elicit antipredator behaviour in the Pacific field cricket, <Emphasis Type="Italic">Teleogryllus oceanicus</Emphasis> (Orthoptera: Gryllidae)

Bats that glean prey (capture them from surfaces) produce relatively inconspicuous echolocation calls compared to aerially foraging bats and could therefore be difficult predators to detect, even for insects with ultrasound sensitive ears. In the cricket Teleogryllus oceanicus, an auditory interneuron (AN2) responsive to ultrasound is known to elicit turning behaviour, but only when the cricket is in flight. Turning would not save a cricket from a gleaning bat so we tested the hypothesis that AN2 elicits more appropriate antipredator behaviours when crickets are on the ground. The echolocation calls of Nyctophilus geoffroyi, a sympatric gleaning bat, were broadcast to singing male and walking female T. oceanicus. Males did not cease singing and females did not pause walking more than usual in response to the bat calls up to intensities of 82 dB peSPL. Extracellular recordings from the cervical connective revealed that the echolocation calls elicited AN2 action potentials at high firing rates, indicating that the crickets could hear these stimuli. AN2 appears to elicit antipredator behaviour only in flight, and we discuss possible reasons for this context-dependent function.     

FEMALE CHOICE FOR AN INDICATOR OF MALE SIZE IN THE SONG OF THE BLACK-HORNED TREE CRICKET,OECANTHUS NIGRICORNIS (ORTHOPTERA: GRYLLIDAE: OECANTHINAE)

The calling song of male crickets, including Oecanthus nigricornis (Walker), attracts females for mating and provides a model system of sexual communication. We give the first conclusive identification of a feature of cricket song that is both attractive to females and indicates a phenotypic feature (body size) that determines male mating success and female reproductive benefits. We do this by first testing for correlations between song characteristics and aspects of male phenotype that are hypothesized to indicate male quality. We show that song is a reliable indicator of male size and male age, and that large male size is associated with increased female fecundity. We then use playbacks of synthetic songs that mimic natural variation in song parameters to study song preferences and we compare preferences under different presentation regimes to determine whether choices are based on relative song quality or some fixed criterion. Females show a preference for the lower frequency songs produced by large males, but only during simultaneous playbacks. Thus female choice is based on the relative quality of calls that can be sampled simultaneously. These results provide strong support for the hypothesis that females use variation in calling song to assess male mate quality.     

Convergent song preferences between female field crickets and acoustically orienting parasitoid flies

Traits that increase the attractiveness of males to femalesoften make them more conspicuous to predators. In the fieldcricket (Gryllus lineaticeps), males are attacked by parasitoidtachinid flies (Ormia ochracea) that locate males through theircalls. Female flies larviposit on crickets and the larvae burrowinto and feed on the cricket, killing the cricket upon emergence.To determine whether traits preferred by females increase amale's risk of attracting a predator, I examined the effectof variation in male singing behavior on mate and predator attraction.Both female crickets and female flies preferred male callingsongs with higher chirp rates, longer chirp durations, and higherchirp amplitudes. In addition, both female crickets and femaleflies preferred male calling songs with higher chirp rates andlonger chirp durations, even when these songs were of loweramplitude. These results suggest that sexual selection by femalechoice will favor the evolution of higher chirp rates and longerchirp durations. However, call types that increase a male'sattractiveness to females also appear to increase a male's riskof attracting parasitoids. Sexual and natural selection appearto have opposing effects on the evolution of male singing behaviorin this species.[Behav Ecol 7: 279-285 (1996)]     

Horn length is not correlated with calling efforts in the horn‐headed cricket Loxoblemmus doenitzi (Orthoptera: Gryllidae)

Field cricket species are ideal model organisms for the study of sexual selection because cricket calling songs, used to attract mating partners, are pronouncedly sexually dimorphic. However, few studies have focused on other sexually dimorphic traits of field crickets. The horn‐headed cricket, Loxoblemmus doenitzi, exhibits exaggerated sexual dimorphism in head shape: males have flat heads with triangular horns, while females lack horns. This study examines the relationship between horn length, male calling efforts and diet quality. Horn length was not found to be significantly correlated with calling efforts. When diet was manipulated for late‐stage nymphs, calling efforts in the group with poor‐quality diet treatment was significantly lower than that of crickets in the group with high‐quality diet treatment. However, horn length was not affected by diet quality. The implication of these results in the context of the evolution of multiple signals and sexual dimorphism is discussed.     

Variation and Repeatability of Calling Behavior in Crickets Subject to a Phonotactic Parasitoid Fly

Male Teleogryllus oceanicus (Orthoptera: Gryllidae) produce a conspicuous calling song to attract females. In some populations, the song also attracts the phonotactic parasitoid fly Ormia ochracea (Diptera: Tachinidae). I examined the factors affecting calling song by characterizing the calling behavior of caged crickets from an area where the fly occurs. Calling activity (proportion of time spent calling) was repeatable and a significant predictor of female attraction. However, calling activity in the parasitized population was lower than in an unparasitized Moorea population (Orsak, 1988), suggesting a compromise between high activity to attract females and low activity to avoid flies. Calling activity peaked simultaneously with fly searching, so crickets did not shift to calling when the fly is less active. Males harboring larvae did not call less than unparasitized males; however, a more controlled study of the effects of parasitization on calling behavior is needed to evaluate this result. The results are discussed in the context of other studies of the evolutionary consequences of sexual and natural selection on cricket calling behavior.     

Spatio-Temporal Dynamics of Field Cricket Calling Behaviour: Implications for Female Mate Search and Mate Choice

Amount of calling activity (calling effort) is a strong determinant of male mating success in species such as orthopterans and anurans that use acoustic communication in the context of mating behaviour. While many studies in crickets have investigated the determinants of calling effort, patterns of variability in male calling effort in natural choruses remain largely unexplored. Within-individual variability in calling activity across multiple nights of calling can influence female mate search and mate choice strategies. Moreover, calling site fidelity across multiple nights of calling can also affect the female mate sampling strategy. We therefore investigated the spatio-temporal dynamics of acoustic signaling behaviour in a wild population of the field cricket species Plebeiogryllus guttiventris. We first studied the consistency of calling activity by quantifying variation in male calling effort across multiple nights of calling using repeatability analysis. Callers were inconsistent in their calling effort across nights and did not optimize nightly calling effort to increase their total number of nights spent calling. We also estimated calling site fidelity of males across multiple nights by quantifying movement of callers. Callers frequently changed their calling sites across calling nights with substantial displacement but without any significant directionality. Finally, we investigated trade-offs between within-night calling effort and energetically expensive calling song features such as call intensity and chirp rate. Calling effort was not correlated with any of the calling song features, suggesting that energetically expensive song features do not constrain male calling effort. The two key features of signaling behaviour, calling effort and call intensity, which determine the duration and spatial coverage of the sexual signal, are therefore uncorrelated and function independently.     

A Study of the Behaviour of the Australian Field Cricket Teleogryllus commodus (Walker) (Orthoptera: Gryllidae) in the Field and in Habitat Simulations

The behaviour of T. commodus (Walker) in the field and in simulated natural habitats is described. Regular predictable sequences of behaviour are represented by an ethogram. Most behaviour was centred around burrows or sheltered sites. Burrows appeared to be a limiting resource and there may be behavioural dimorphism in ♂ ♂ (burrower and non-burrower strategies). Individuals were found to form gregarious clusters and appeared to be attracted to areas already occupied by crickets. Territorial spacing and other social interactions occurred within these clusters. ♂ ♂ and ♀ ♀ were found to be mobile, and moved continually between sites. The movement of ♂ ♂ and ♀ ♀ between burrows (calling sites) was measured. Adult ♂ ♂ never remained at a burrow for longer than two days. In simulated natural habitats ♂ ♂ moved in response to two factors: first, and most common, as a result of eviction by other ♂ ♂ second, as a response to the absence of ♀ ♀. When cricket density was increased in habitat simulations crickets clustered at calling sites. The adaptive significance of T. commodus behaviour is discussed.     

Abdominal Tubercles of Adult Male Camel Crickets, Pristoceuthophilus marmoratus Rehn (Orthoptera: Rhaphidophoridae), Produce Cues Attractive to Females

In contrast to many crickets and katydids, adult male camel crickets (Orthoptera: Raphidophoridae) do not stridulate and do not produce audible air-borne calling songs to attract females for mating. The mating behavior of most camel cricket species is undescribed; how pair-formation occurs is unknown, but chemical cues seem one likely possibility. In the camel cricket Pristoceuthophilus marmoratus Rehn, we test (1) the role of chemical cues in conspecific attraction, and (2) the role of the abdominal tubercles of adult males in producing those cues. We show (1) that virgin adult females are attracted to paper towels previously exposed to adult males, and (2) that paper towels previously exposed to adult males with exposed tubercles are more attractive than paper towels previously exposed to adult males with experimentally closed tubercles. In addition, we present Scanning Electron Microscope photos of adult male tubercle structure that are consistent with their putative role in producing chemical cues.     

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.     

the effect of pair formation on diel calling patterns in two cricket species,Gryllus veletis andGryllodes sigillatus (Orthoptera: Gryllidae)

After pair formation, male crickets should reduce calling to minimize the risks to males of attracting predators and/or rivals. We tested this hypothesis in two cricket species, one in which males exhibit a high mating propensity (Gryllus veletis)and another in which the mating propensity of males is constrained by the manufacture of elaborate, bipartite spermatophores (Gryllodes sigillatus).Calling durations of male G. veletisdeclined precipitously after the introduction of females but remained unchanged in G. sigillatus.We attribute the asymmetric effect of female proximity on male calling to differences in the mating propensity of males of the two species. Male G. veletisabstain from further calling in favor of repeated matings with the same female. Male G. sigillatusprobably lack the opportunity to mate repeatedly with the same female and, thus, resume calling shortly after mating to increase their probability of attracting additional mates.     

Male hosts are responsible for the transmission of a trophically transmitted parasite, Pterygodermatites peromysci, to the intermediate host in the absence of sex-biased infection

Field studies have identified that male-biased infection can lead to increased rates of transmission, so we examined the relative importance of host sex on the transmission of a trophically transmitted parasite (Pterygodermatites peromysci) where there is no sex-biased infection. We experimentally reduced infection levels in either male or female white-footed mice (Peromyscus leucopus) on independent trapping grids with an anthelmintic and recorded subsequent infection levels in the intermediate host, the camel cricket (Ceuthophilus pallidipes). We found that anthelmintic treatment significantly reduced the prevalence of infection among crickets in both treatment groups compared with the control, and at a rate proportional to the number of mice de-wormed, indicating prevalence was not affected by the sex of the shedding definitive host. In contrast, parasite abundance in crickets was higher on the grids where females were treated compared with the grids where males were treated. These findings indicate that male hosts contribute disproportionately more infective stages to the environment and may therefore be responsible for the majority of parasite transmission even when there is no discernable sex-biased infection. We also investigated whether variation in nematode length between male and female hosts could account for this male-biased infectivity, but found no evidence to support that hypothesis.     

INBREEDING AND ADVERTISEMENT CALLING IN THE CRICKET TELEOGRYLLUS COMMODUS: LABORATORY AND FIELD EXPERIMENTS

If sexually selected traits reveal a male's heterozygosity or condition to females, then such traits should exhibit declines with inbreeding. We tested this by examining the effect of inbreeding on advertisement calling in male crickets Teleogryllus commodus. We investigated the effect of one generation of full‐sibling mating on calling effort and fine‐scale call structure. Inbreeding reduced calling effort but had no effect on call structure. We then compared the attractiveness of inbred and outbred calls in the field by monitoring how many wild females were attracted to each call type. From the field data, we conducted a selection analysis to identify the major axes of linear and nonlinear multivariate sexual selection on call structure. A comparison of multivariate attractiveness of inbred and outbred calls along each major axis of selection revealed no difference in attractiveness. Our results suggest that inbred male calls have a fine‐scale structure that is no less attractive to females than that of outbred calls. However, because inbred males call less often, and female T. commodus prefer males with a higher calling effort, inbred males will suffer reductions in mating success. Females who base mate choice on call rate are therefore using a signal correlated with male heterozygosity and/or condition.     

Cricket calling communities as an indicator of the invasive ant <Emphasis Type="Italic">Wasmannia auropunctata</Emphasis> in an insular biodiversity hotspot

Invasive species are a major concern for the maintenance of ecosystem services and biodiversity but are difficult to mitigate. Upstream solutions to prevent their impact, including their detection, are needed. Wasmannia auropunctata, an invasive ant living in vagile supercolonies, is especially hard to track and is a major threat for tropical ecosystems and local animal communities. As part of such tropical communities, crickets are sensitive to ecological conditions, easy to collect, detectable and identifiable through their species-specific calls. Here, we evaluated the use of an acoustic community of crickets as an indicator of the presence of W. auropunctata in New Caledonia. We evaluated the dominance of the crickets in the soundscape, describe the cricket community structure and diversity along a shrubland to forest gradient, characterize these cricket communities structure and diversity in the light of ongoing invasion by W. auropunctata, and identify cricket species’ indicators of the invasion. Acoustic recordings collected on 24 sites were described using human-listening and spectrographic visualization. The results demonstrated a clear dominance of the cricket group in the New Caledonian nocturnal soundscapes. Each habitat harbored a specific acoustic cricket community related to specific environmental attributes including vegetation height, daily variation of humidity and temperature. The presence of W. auropunctata was significantly associated with a lower cricket acoustic activity and species richness at night. Of the 19 species detected, four nocturnal species were identified as indicator of non-invaded forests and preforests. This work supports the use of acoustic as an alternative method to detect invasion.