Female Calls Research Articles

Comparison of reproductive strategies and raiding behaviour in facultative and obligatory slave-making ants: the case of Formica sanguinea and Polyergus rufescens

A review of field and laboratory research concerning raiding behaviour, mating strategies and colony founding in Formica sanguinea and Polyergus rufescens (respectively facultative and obligatory parasites of the Serviformica species) is presented. The analysis and comparison of these crucial and peculiar moments in the life cycle of dulotic colonies may be a valid tool to clarify the evolutionary origins of slavery in ants.¶Concerning the reproductive behaviour, F. sanguinea females mate only in nuptial flights. P. rufescens females mate on the ground around their natal nest, or return to a dulotic colony after mating flights and wait for a raid, or mate directly during a raid. Moreover, field observations suggest that F. sanguinea adopts a strategy similar to the "male aggregation syndrome", whereas P. rufescens mating strategy can be considered similar to the "female calling syndrome". In the field, newly-mated queens of both slave-makers participate in raiding swarms: following a slave raid is an advantageous strategy to locate and invade host nests and to establish a new dulotic colony.¶For colony formation, F. sanguinea presents a great variety of possible strategies (independent foundation and dependent foundation including alliance, adoption, usurpation, and brood sack). This provides evidence of a behavioural plasticity that confirms its nature as a facultative parasite. On the contrary, P. rufescens depends only on usurpation, during which the Dufour's gland contents seem to play a crucial role in the appeasement of the residents of the target colony.¶Also the raiding behaviour of F. sanguinea is less specialized than that shown by P. rufescens. In fact, in the obligatory slave-maker the important role of scouts in the organization of slave-raids is confirmed, which are rapid and effective. By contrast, raids of F. sanguinea may be regarded as a continuation and expansion of common foraging and predatory activity, as predicted by Darwin's hypothesis for the origin and evolution of slavery in ants. Nevertheless, the intraspecific raids conducted by P. rufescens emphasize also the important role of territorial competition as evolutive cause of dulosis.

The phenology of a Neotropical ant assemblage: evidence for continuous and overlapping reproduction

Reproductive phenologies reflect the interaction between the mating system of a taxon and the local environment. Ant colonies reproduce and disperse via the flights of winged alates. Few data exist on the reproductive phenologies of ant assemblages. Here we analyze the reproductive phenologies of 81 common ant species from 23,182 individuals collected over 3 years on Barro Colorado Island, Panama (BCI). Species ranged from highly synchronous to continuous fliers, but showed a median flight duration of at least 8 of 13 lunar months. In two statistical analyses (variance ratio test and Spearman rank correlations), 84% (16 of 19) of ant genera had species trending toward positively associated phenologies, more than expected by chance (P<0.00036 by a binomial test). Thus, there was little evidence for the hypothesis that competition for limiting resources staggers congeneric flights and ultimately promotes reproductive isolation. On the contrary, the timing of reproduction, and its synchrony, tended to be conserved within genera and subfamilies. These results closely match phenological studies of plant assemblages. The continuous reproduction and small colony size of many species in this study suggest that the female calling syndrome, a poorly documented mating system in ants, may be common on BCI.

Female reciprocal calling in the Iberian midwife toad (Alytes cisternasii) varies with male call rate and dominant frequency: implications for sexual selection.

Male midwife toads (Alytes cisternasii) responded differently depending on the call frequency and call rate of other males. I tested female Iberian midwife toads with the same set of stimuli used earlier with males. Females responded faster to high call rates, and female vocal activity was greater in response to low-frequency male calls. Thus, in both sexes, the vocal response differs in the same direction according to signal frequency variation, but the magnitude of the response is greater in males than in females. In the light of these results, I discuss the implications for sexual selection of this reciprocal calling.

Individuality and male discrimination of female copulation calls in the yellow baboon

In a wide variety of animal species, females produce vocalizations just before, during or immediately after copulation. These calls are thought to be sexually selected traits that function to incite males to compete for access to the calling females in such a way that, by calling, females maximize the quality and/or the number of their mating partners. The signalling of individual identity within these vocalizations, in conjunction with male discrimination between females on this basis, would have important implications for their function. I analysed the copulation calls of free-ranging yellow baboons,Papio cynocephalus cynocephalus , to examine whether sufficient acoustic cues existed to broadcast information on the individual identity of the caller. Discriminant function analysis indicated that calls could be assigned to the correct female with a high degree of accuracy, both when considering calls given throughout the menstrual cycle and also those given only during the period of likely conception (when the sexual swelling is at its largest). A playback experiment showed that consorting male baboons were able to discriminate the copulation call of their consort female from that of another cycling female. I discuss the implications of individuality of female copulation calls and males' perception of this variability.

Vocal traits of hybrid fur seals: intermediate to their parental species

Vocal communication is important for species recognition in colonial breeding species such as fur seals, especially where closely related species that can hybridize breed sympatrically. This is the first study to describe the calls of hybrid fur seals. We investigated whether these vocalizations are intermediate to those of their parental species (Antarctic,Arctocephalus gazella , subantarctic, A.tropicalis, and New Zealand, A.forsteri) and discuss the evolutionary implications of hybrids having intermediate vocal traits. Hybrid males' bark calls were intermediate between two distinct groups formed by A.tropicalis and A.gazella/A.forsteri. Patterns of intermediate call characteristics were also discernible for pup attraction calls (given by females) but not for full threat calls (given by males), nor female attraction calls (given by pups); however, for all call types hybrid calls were distinct from those of their parental species. The pattern of hybrid calls being intermediate is consistent with the expectation that call traits are genetically inherited.

Comparison of Substrate-Borne Vibrational Signals ofTwo Stink Bug Species, &lt;I&gt;Acrosternum hilare&lt;/I&gt; and &lt;I&gt;Nezara viridula&lt;/I&gt; (Heteroptera: Pentatomidae)

Substrate-borne vibrational signals (songs) were recorded from the green stink bug, Acrosternum hilare (Say) and the southern green stink bug, Nezara viridula (L.). Female A. hilare emitted one song type in the calling phase of mating behavior, and the production of this song was stimulated by male presence or calling. The temporal characteristics of the pulses and pulse trains of this song were similar to the narrow-band type of pulse trains that constituted the N. viridula female calling song. Male A. hilare produced two different songs, each associated with a different phase of mating behavior. In the calling phase, males produced a song composed of regularly repeated, complex pulse trains whose temporal structure resembled that of the N. viridula male courtship song. In the courtship phase of behavior, males of A. hilare emitted a song that terminated female singing. The pulses of this song had similar temporal characteristics to those of the narrow-band type of the N. viridula male calling song. Immediately after initiating copulation, A. hilare pairs emitted another song, which had no counterpart in the repertoire of N. viridula or other pentatomid species that have been examined. In contrast, males of A. hilare did not appear to produce a song equivalent to the N. viridula male rival song, and neither sex of A. hilare produced songs equivalent to the broad-band pulses and pulse trains found within male and female N. viridula calling songs. Orientation of males toward females was mediated by the female calling song, which had similar spectral and temporal characteristics in both species. Male songs of the two species, although they shared some spectral characteristics, differed in temporal structure and in the contexts in which they were emitted.

Sex differences in discrimination of vocal communication signals in a songbird

Vocal communication between zebra finches, Taeniopygia guttata, involves a variety of calls, as well as song. One of these, the long call, is exchanged between individuals in specific social contexts. Male long calls differ from the simpler unlearned long calls of females in one or more learned acoustic features: short, stable duration, elevated fundamental frequency and presence of fast frequency modulations. When species-specific long-call signals produced by male and female conspecifics were played back to adult male and female zebra finch subjects, the birds responded by calling. Males consistently responded much more to female long calls than to male long calls. Females also responded more to female long calls, but the effect was weaker. The responses of females had a correlation with stimulus duration that accounted for most of the higher response to female long calls. Males, like females, responded more to longer long calls, but also showed a step-like increment in responses to all female stimuli. Male birds effectively classified the stimuli by gender; females showed much weaker gender discrimination. The contributions of specific acoustic features to these discriminations were then explored by testing the birds with synthetic versions of natural calls and simplified sounds based on mathematical functions in which acoustic parameters could be independently specified. Male birds showed response functions with changes at particular values of fundamental frequency, stimulus duration and initial modulation frequency, suggestive of category boundaries within these parameters. Female response functions showed changes only for duration. When these response functions were used to predict responses to natural stimuli with given parameter values, the observed response patterns for natural stimuli in the two sexes were reproduced. The decisive gender categorization shown by males thus emerges from categorical evaluation of multiple stimulus parameters.

Preliminary comparison of calls of the hybridizing fur seals Arctocephalus tropicalis and A. gazella

The Antarctic fur seal (Arctocephalus gazella) and the Subantarctic fur seal (A. tropicalis) hybridize on a relatively small scale at Marion Island. To date the description of calls published for A. tropicalis and A. gazella are fragmented and not easily compared. We compare the vocal signalling of males and females of the two species of fur seals to aid understanding of the factors involved in hybridization. Five call types were compared: barking, guttural challenges and territorial calls emitted by adult males; the pup attraction call used by adult females and the response: female attraction call emitted by pups. The calls emitted by males of the two species have certain similarities but are separated by multivariate analyses. By contrast, the calls of females and pups of the two species are more similar and do not cluster separately. Since many of the differences in male calls are audible to the human ear, female seals can presumably also hear these differences and we suggest that interbreeding of the two fur seal taxa is not caused by similarity in male vocal communication. Following this preliminary study, further behavioural studies are required for a fuller understanding of hybridization in these animals.

Fat reserves and perceived predation risk in the great tit, Parus major.

The fat reserves of small birds are built up daily as insurance against starvation. They are believed to reflect a trade-off between the risks of starvation and predation such that in situations of high predation risk birds are expected either to reduce their fat reserves in response to mass-dependent predation risk or to increase them in response to foraging interruptions. We assessed the effect on fat reserves of experimentally altering the perceived (but not the actual) risk of predation of wild great tits at a winter feeding site. The perceived predation risk was alternated between 'safe' and 'risky'. Increasing the perceived risk of predation involved 'swooping' a model sparrowhawk over the feeder at four unpredictable times each day using a remote mechanism We produce evidence that the experiment was suceessfull in altering the perceived risk of predation. As predicted from the hypothesis of mass-dependent predation risk, great tits (Parus major) carried significantly reduced fat reserves during the 'risky' treatment. Furthermore, dominant individuals were able to reduce their reserves more than subordinates. As birds returned to feeders within seconds after a predator 'attack', the reduction in fat reserves cannot be attributed to an interruption in feeding.

Songs of Holcostethus strictus (Fabricius): a different repertoire among landbugs (Heteroptera: Pentatomidae)

Songs emitted during mating by male and female Holcostethus strictus were recorded as substrate vibrations. Spectra of the vibrational signals have a dominant frequency peak between 100 and 260 Hz and in this respect reflect the general characteristic of the family Pentatomidae. Songs of H. strictus differ from the song repertoire of the southern green stink bug Nezara viridula (L.) (Pentatomidae) in many respects. The female calling and courtship songs differ in echeme and phrase duration. The male calling song is composed of spectrally different subunits. The male courtship song is characterised by three types of spectrally and temporally different echemes. The male copulatory song is composed of echemes of two types, which constitute a phrase of less regular temporal structure. In H. strictus, males start to sing first and female songs are less complex than in N. viridula. The female calling song is evoked by male calling and does not trigger male response. The female and male courtship song phrases are superimposed on one another and we have not observed any obvious regularity in their exchange. The possible role of different songs in H. strictus is discussed and compared with that in other pentatomide landbug species.

CAN TESTOSTERONE INDUCE THE MALE WHISTLE-SHAKE CALL IN FEMALE SHELDUCKS TADORNA TADORNA?

ABSTRACT We investigated by application of testosterone-proprionate whether females of the dimorphic Shelduck Tadorna tadorna are capable of producing vocalisations typical of the male sex. We found that hormone-treated females generated the whistle-shake call, an epigamie vocalisation pattern of male Shelducks. Although the female whistle- shake call was male-like in its syntactic form, we observed significant differences in both the phonetic and temporal characteristics of male and female whistle-shake calls. None of the testosterone-treated females was found to produce real male-typical elements. All whistle-shake calls of these females consisted of elements which are also used in calls of untreated females, e.g. the agagak-call. The present findings indicate that the sexual dimorphism in Shelduck vocalisations is not due to early organising actions of sex hormones influencing the differentiation of the brain. It results mainly from adult sex differences in the endogenous testosterone production. Only males produce testosterone in considerable amounts. The inability of testosterone-treated female Shelducks to generate male-typical elements might be caused by limitations in the sound-producing organ, the syrinx. Male Shelducks have associated with the syrinx a large resonating chamber, the bulla ossea, which is lacking in females.

The Influence of Substrate on Male Responsiveness to the Female Calling Song in Nezara viridula

The female calling song (FCS) of the southern green stink bug Nezara viridula is composed of vibrational pulse trains that include either short pulses and a long pulse (FCS-1) or just short pulses (FCS-2). Their function in communication was studied by investigating male vibratory responses to natural and artificial signals on artificial and natural substrates. On a loudspeaker membrane, FCS-1 triggered in males from a Slovene and a French population significantly more courtship songs (MCrS) than FCS-2. Experiments with artificial signals showed that male responses are modulated by the duration of pulse trains and pulse repetition time. On a bean plant, males of both populations responded in the same way to the two types of female calling song pulse trains. Moreover, a laser vibrometer study of the transmission of different natural and artificial vibratory signals through the bean plant showed that the pulses of a high repetition rate are prolonged and fused at distances from the emitter. We conclude that female calling song pulse trains of different temporal structure have the same function in vibrational communication of the species. The temporal and spectral structures of the female calling songs of N. viridula are discussed in terms of effective transmission through plants.

The Role of the Dorsomedial Nucleus (DM) of Intercollicular Complex with Regard to Sexual Difference of Distance Calls in Bengalese Finches

The acoustic structures of distance calls in sexually mature Bengalese finches (Lonchura striata var. domestica) show distinct sexual differences. We conducted a neuroethological study to identify the neural mechanism in the brain by which sexually mature male and female birds produce these acoustically different distance calls. Bilateral lesions of the dorsomedial (DM) nucleus of the intercollicular complex, known as the midbrain vocal center, eliminated distance calls in sexually mature males and females, but electrical stimulation of the DM in males and females induced calls that showed sexual differences and were acoustically similar to the distance calls of males and females. These results confirm that the DM in both sexes is one of the nuclei of the vocal control system that controls calling behavior. Neural tracer was injected into the DM in order to identify sexual differences in the neural input and output connections in the DM. Anatomical tracing of DM revealed the existence of labeled somata in the ipsilateral robust nucleus of the archistriatum (RA) in males. After bilateral RA lesions, however, males produced distance calls that were acoustically similar to female distance calls. These results suggest that the DM is one of the nuclei which generate the distance call patterns of both sexes, and that the neural information from the RA to the DM change the distance call pattern of male.

EFFECTS OF SUBLETHAL ESERINE ON THE CHEMICAL COMMUNICATION SYSTEM OF ASIAN CORN BORER, OSTRINIA FURNACALIS (GUENEE)

Abstract Topically applied sublethal doses of eserine may interrupt chemical communication between the two sexes of Asian corn borer, Ostrinia furnacalis (Guenee), by affecting calling and sex pheromone titre released by the females. (1) Studies on the effects of sublethal eserine on the chemical communication system of O. furnacalis indicated that there was a decreasing probability of females calling and sex pheromone titre as the eserine dosage increased from 0.27 to 2 700 ng, with no effect on the periodicity. However, at 2 700 ng, the E/Z ratio of the sex pheromone components was affected. The sexual chemical communication system could not control within narrow level. (2) The recovery test of 27ng-treated female indicated that the calling percentages of the 1st, 2nd and 4th day post-treatment were 50%, 78% and 84% respectively. Sex pheromone titre was 40%, 40% and 80% of control female repectively. There was a trend toward recovery. The sexual chemical communication system could control within narrow level from the 2nd day post-treatment.

Male signalling and lek attractiveness in the Mediterranean fruit fly

I tested the null hypothesis that females of the Mediterranean fruit fly, Ceratitis capitata, were equally likely to visit leks composed of males with high versus low mating success. In laboratory trials, the observed distribution of matings among males differed significantly from that expected by chance, owing primarily to the higher than expected numbers of individuals with low (mated 0–1 days over 6 consecutive observation days) or high (mated 4 or more days) mating scores. I termed these two groups as ‘low’ and ‘high’ maters, respectively. In the field, greater numbers of female sightings were made at artificial leks of high maters than low maters. This result apparently reflected a greater calling propensity among high maters. Slopes of female sightings versus calling level did not differ significantly between leks of low and high maters, suggesting that the observed relationship between calling activity and female sightings was independent of male mating status. Following the same protocol, I conducted a second experiment to examine whether males used the signals of conspecific males to locate lek sites and, if so, whether signal attractiveness varied with male mating ability. Attraction of males to calling conspecifics was far weaker than that observed for females, and over five different trials a total of only seven male sightings were made at any of the established leks.

The structure and function of songs emitted by southern green stink bugs from Brazil, Florida, Italy and Slovenia

Summary Nezara viridula (L.) (Pentatomidae: Heteroptera) from Brazil, Florida, Italy and Slovenia, communicate by vibratory songs associated with long‐range calling and close‐range courting, rivalry and repelling. Each song is composed of spectrally and temporally different units. Spectrally different pulses of duration less than 300 ms are present in the male calling song. The female calling song is characterized by pulse trains composed of pulses shorter than 150 ms and pulse trains composed of a longer (&gt; 700 ms) and shorter (&lt; 250 ms) pulse. Shorter and longer pulses have different spectral characteristics. The male and female courtship songs are characterized by fusion of shorter (&lt; 150 ms) pulses into a pulse train usually followed by a shorter (&lt; 200 ms) postpulse in the case of the male courtship song. The female repelling song is a several seconds long vibration of irregular temporal structure. The short (&lt; 400 ms) male rival song pulses are frequency modulated. The dominant frequency peaks of the songs investigated lie between 70 and 130 Hz. The dominant frequency and the microstructure of song spectra show no population specificity. The average duration varies more in calling than in courtship songs. The repetition time varies extensively in songs of different populations. Normal communication followed by copulation was observed between mates from Slovenia and Brazil and between mates from Florida and Italy. The potential role of different temporal and spectral parameters for species recognition and mate location is discussed in view of the expected distortion of the characteristic signal structure during transmission through plants.

Calling behaviour of adult female Helicoverpa armigera (Hübner) (Lep., Noctuidae) of overwintering generation and effects of mating

The calling behaviour of overwintering generation females of Helicoverpa armigera and the effects of mating were studied in the laboratory at 24 ± 1°C and under reversed light‐dark cycle (16 h light : 8 h dark). Age had a significant influence on calling patterns. Based on calling age, mean number of calling bouts and total calling length of virgin females increased significantly, and mean onset time of calling advanced significantly from calling day 1 to subsequent calling days. Females of the overwintering generation exhibited more short bouts in calling, and some females that initiated calling on a previous day did not call on subsequent days. Mating had no effect on the overall patterns, but did affect calling behaviour. Mated females did not resume calling after mating during the same scotophase and, on the day following mating, mated females called less frequently and for a shorter duration, but thereafter increased to the same level of virgin females of the same calling age. Furthermore, as the moth aged, the percentage of mated females calling was lower than that of virgin females.

Perception of female reproductive state from vocal cues in a mammal species.

While acoustic signalling by males is known to affect male-male competition, mate attraction and the timing of ovulation, the extent to which sexual selection has shaped the evolution of female acoustic signals is poorly understood. Among mammals, experimental evidence indicates that females attract mating partners by using olfactory and visual signals to advertise their reproductive state. Whether or not males ascertain female reproductive state from vocal signals has, however, never been systematically tested. In this study, we use playbacks of recorded vocalizations to demonstrate that male Barbary macaques, Macaca sylvanus, can discriminate between female copulation calls given at different stages of the oestrous cycle, responding more strongly to those given around the time when conception is most likely to occur. Acoustic analysis suggests that the mean dominant frequency of call units and a number of temporal parameters could provide males with the information necessary to discern the proximity of ovulation in this way Our results provide the first experimental evidence that the calls of female mammals may contain information on reproductive state, which males can perceive and use in such a way as to increase their reproductive success.

Circadian locomotor rhythm masked by the female reproduction cycle in cockroaches

Summary Blattella bisignata (Brunner) and B. germanica (L.) are oviparous cockroaches with cyclic reproductive behaviour, but in B. germanica only males show circadian rhythmicity of locomotion at 28°C and DD (constant darkness). In B. bisignata, males and virgin females cockroaches entrained by light–dark cycles show free‐running rhythmicity in DD, and most activities occur during the subjective night. Daily locomotor activities of virgin females show cyclic changes that coincided with ovarian development. Virgin females also exhibit calling behaviour during the subjective night, and this shows a free‐running rhythm. Male mate‐finding locomotion and female calling behaviour are under circadian control, so the timing for both behaviours is synchronized. However, most mated females do not show a locomotor free‐running rhythm under DD conditions. Our results indicate that only mated females could not express a circadian locomotor rhythm. Pregnancy reduces a female’s locomotory intensity and masks the expression of a circadian locomotor rhythm. We attribute the differences in circadian locomotory rhythms between these two species to their living environments and mate‐finding strategies.

Generating Sexually Differentiated Vocal Patterns: Laryngeal Nerve and EMG Recordings from Vocalizing Male and Female African Clawed Frogs (Xenopus laevis)

Male and female African clawed frogs (Xenopus laevis) produce sexually dimorphic vocalizations; for males these include advertisement, amplectant, and growling calls, whereas female calls include ticking. Previous studies have shown that the vocal organ, the larynx, of the sexes differs in physiological properties that parallel vocal differences. However, it was not clear whether these characteristics are sufficient to explain sex differences in vocal behavior. To examine the contribution of the CNS to generating vocal patterns, we developed a preparation in which both laryngeal nerve activity and electromyograms can be recorded from awake, vocalizing frogs. Recordings reveal that the CNS of the two sexes produces patterned activity that closely matches each vocalization whereas the larynx faithfully translates nerve activity into sound. Thus, the CNS is the source of sexually differentiated vocalizations in Xenopus laevis. Furthermore, detailed analyses of compound action potentials recorded from the nerve lead us to hypothesize that neuronal activity underlying different male call types is distinct; some calls are likely to be generated by synchronous firing of motoneuron populations of either constant size or progressively larger sizes, whereas others are generated by asynchronous activity of motoneurons, a pattern shared with vocal production in females. We suggest that these distinct neuronal activity patterns in males may be subserved by two populations of motor units in males that can be distinguished by the strength of the neuromuscular synapse.