Song Components Research Articles

The effect of past condition on a multicomponent sexual signal.

Sexual-selection theory predicts that multiple signals may reveal male condition at different stages of life, thus allowing females to make a more reliable assessment of male quality. While the effect of current condition on signal design is well established, few studies have experimentally investigated the effects of past condition. We therefore manipulated the nutritional condition of male nymph field crickets Gryllus campestris and assessed the enduring effects on multiple components of the adult calling song. Food-restricted males had longer nymphal development times and smaller adult body sizes than nymphs with ad libitum food access. Nymphal feeding conditions specifically affected the allometric relationship between body size and harp size, as food-restricted males developed comparatively small harps, leading to a calling song of higher carrier frequency than that produced by similar-sized control males. Other calling-song components, notably chirp rate and chirp intensity, were not affected by the nymphal food treatment, exposing carrier frequency as the key component indicating past condition. In a previous study we established chirp rate as the sole indicator of current condition. The combined results represent experimental evidence of a multicomponent sexual signal that provides distinct information on male condition during different stages of life.

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.

Quantitative trait loci affecting a courtship signal in Drosophila melanogaster.

Courtship plays a major role in the sexual isolation of species, yet the genetics underlying courtship behaviour are poorly understood. Here we analyse quantitative trait loci (QTL) for a major component of courtship song in recombinant inbred lines derived from two laboratory strains of Drosophila melanogaster. The total variance among lines exceeds that between parental strains, and is broadly similar to that seen among geographic strains of the Cosmopolitan form of this species. Previous studies of the quantitative genetics of fly song have implied a polygenic additive inheritance with numerous genes spread throughout the genome. We find evidence for only three significant QTLs explaining 54% of the genetic variance in total. Thus there is evidence for a few large effect genes contributing to the genetic variance among lines. Interestingly, almost all of the candidate song genes previously described for D. melanogaster do not coincide with our QTLs.

Song Sharing in Neighboring and Non‐Neighboring Thrush Nightingales (Luscinia luscinia) and its Implications for Communication

In many passerines, males have repertoires of different songs of which some songs are often shared with other males. Sharing of song repertoires among males can provide insights into the context in which songs were acquired and on the role of song repertoires in inter‐ and intrasexual communication. Here we studied repertoire sharing in male territorial thrush nightingales (Luscinia luscinia). We compared male vocal repertoires of the basic song components, full songs, and the sequencing of songs in a bout. The results show that males differed significantly in the size of their song repertoires but not in the size of the repertoire of basic song components. Moreover, they shared almost all (80%) the repertoire of song components but only 30% of their song types. Neighboring males shared significantly more song types than did non‐neighboring males but interestingly they did not share more basic song components than non‐neighboring males. These results show that the repertoire of basic song components is under much less sexual selection than the size of song repertoires. Sharing of song repertoires among neighbors presumably results from repertoire conversion over time and from males returning to their territories in the following season. Repertoire sharing then can be an indicator of territory tenure and thus it can be important in repelling rivals and in female choice.

DECISIONS DURING COURTSHIP BY MALE AND FEMALE MEDFLIES (DIPTERA, TEPHRITIDAE): CORRELATED CHANGES IN MALE BEHAVIOR AND FEMALE ACCEPTANCE CRITERIA IN MASS-REARED FLIES

Analyses of more than 300 videotaped courtships of wild and mass-reared medflies from Costa Rica showed that the tendency for male and female to align themselves facing directly toward each other increased, and that the distance between them decreased as courtship proceeded. More direct alignments and shorter distances between the flies at the moment the male jumped onto the female were correlated with greater female acceptance of copulation. There were no consistent differences in durations of components of intermittent buzzing songs or male size between successful and unsuccessful courtship in either strain. Several possible cues may release different courtship responses: males of both strains tend to initiate both continuous vibration and intermittent buzzing after reduction of the distance to the female; slow creeping toward the female was associated with longer courtships that had failed to lure the female close; and females tended to turn to face more directly toward the male soon after the male began continuous vibration, and especially after he began intermittent buzzing. Females became progressively more immobile as courtship progressed, especially soon after intermittent buzzing began. There were numerous differences between strains. Mass-reared males were more likely to mount females without previous courtship than were wild males. Wild males initiated continuous wing vibration when farther from the female and when the female was looking less directly toward them, but the two strains did not differ in the distances and angles at which males initiated intermittent buzzing and jumped. Wild males were more likely to creep toward the female during intermittent buzzing. Mass-reared females but not wild females were more likely to copulate when the proportion of time the male had spent in intermittent buzzing was low, and if the courtship began when the flies were nearer each other. Wild but not mass-reared females were less likely to copulate if courtship was shorter. Possible coevolution of female responses with the five different male courtship traits that differ between mass-reared and wild flies are discussed.

Imitation and Invention in Song Learning in Nightingales (Luscinia megarhynchos B., Turdidae)

Song learning in oscine birds is often defined solely as a process of song imitation; nonetheless, not all songs produced by laboratory‐tutored birds are imitations of the model songs. If song learning were strictly a process of imitation, these non‐imitated songs (inventions) would be expected to contain no learned attributes. To determine whether species‐typical song attributes can be learned in the absence of imitation, we compared the imitations and inventions of laboratory‐tutored nightingales (Luscinia megarhynchos B.) with the songs of wild nightingales and the songs of laboratory‐reared, untutored nightingales. The species‐typical song attribute measured was stereotypy. We quantified stereotypy by four variables: (1) percentage of notes shared between two renditions of the same song type (2) difference in repetition rates of the same trill in two renditions of the same song type (3) acoustic similarity of the same note in two renditions of the same song type, and (4) acoustic similarity of the same note repeated within a trill. Wild songs and imitated songs were significantly more stereotypical than the songs of untutored birds for all measures. For the percentage of notes shared (1), and the acoustic similarity of notes in two renditions of the same song type (3), invented songs did not differ from the songs of untutored birds, suggesting that imitation is necessary for the acquisition of these song characteristics. However, invented songs were significantly more stereotypical than the songs of untutored birds for measures of stereotypy related to trills (2 and 4), and neither imitated nor invented songs differed significantly from the songs of wild birds in terms of trill rate stereotypy (2). Thus, it appears that the process of learning to produce trills may differ from the process of learning non‐repetitive song components: increased stereotypy in trills occurs even when the trills themselves are not copied from song models. Strict imitation does not fully account for the acquisition of some learned song attributes.

The Effect of Male Competition on the Courtship Song of Drosophila melanogaster

The courtship song of Drosophila has been extensively used as a model system for studies of sexual selection and species recognition. Traditionally, the courtship song has been recorded from males placed individually with a female. However, under natural conditions females are exposed to multiple courting males, and the effect of their joint signal on mate recognition by the female is not yet understood. Here, we recorded the courtship behavior of D. melanogaster males singing either individually to a female lpar;1:1) or in the presence of an additional male lpar;2:1). We compared the structure of the male song in the two experimental designs. Our results show that when two males courted a female their songs could overlap each other. Males produced a significantly different signal in the presence of competition; the duration of each song component was significantly shorter and the rate of singing was markedly lower. The present study demonstrates that male competition can dramatically alter the acoustic signal detected by the female.

Talking Back: Sending Soil Vibration Signals to Lekking Prairie Mole Cricket Males1

SYNOPSIS. The male prairie mole cricket, Gryllotalpa major, native of the tallgrass prairie of the south central U.S., constructs a specialized acoustical burrow in the spring in the prairie soil from which he generates an airborne calling song that attracts flying females for mating. Males do not phonorespond to manipulations involving playbacks of airborne sounds. At the same time, vibrations with the same temporal scale and pattern as the airborne signal are produced in the substrate through an unknown mechanism. These ground vibrations can be distinguished from background vibrations in the soil at distances up to 3 m depending on soil conditions and conditions that control the background vibration environment (e.g., wind, highway traffic). We hypothesize that males use the vibration component of the call as information for spacing as they form display arenas, or leks. We used modified field recordings of soil vibrations from singing males with an electromechanical vibration exciter to simulate the vibration component of a calling song in playback experiments. Airborne sounds of males were monitored for two minutes before and two minutes after the introduction of the ground vibration stimulus with a tape recorder microphone placed 20 cm from the burrow opening. Males did respond to the manipulation experiment; although, we observed individual variation in the level of response.

Geographical variation in calling song of the field cricket Teleogryllus oceanicus: the importance of spatial scale

Abstract We compared calling songs of the field cricket Teleogryllus oceanicus from 15 sites within six regions of two continental areas, Oceania and Australia. The cricket was introduced to Hawaii, where it is subject to an acoustically orienting parasitoid fly not found elsewhere in its range. In a principal components analysis (PCA) of song from all populations combined, the first five components had eigenvalues greater than one, and collectively accounted for over 80% of the total variation. Means for all song components varied significantly among sites, and different components varied at the three levels of analysis (continent, region and site). The principal way in which sites differed was along a gradient in increasing song length, pulse duration and intervals between song elements. Crickets from Oceania had a significantly greater variance in their song than Australian crickets, driven largely by the high variance in Hawaii. Geography explained a substantial amount of variation in song, despite the likelihood of serial bottlenecks having occurred as the species moved from island to island. Because female crickets appear not to focus on the short chirp as a component of mate choice, a lack of selection may allow this song component to vary more widely.

Are text and tune of familiar songs separable by brain damage?

The recognition of text and tune in songs was examined in a music-agnosic patient and five matched controls. Listeners had to focus on one component of the song at a time (text or music) and had to decide whether the component was familiar or unfamiliar. Songs were either matched (i.e., an original familiar or an original unfamiliar song) or mismatched (a combination of a familiar component with an unfamiliar one). Normal listeners displayed response patterns that are congruent with those obtained previously in different experimental settings and which showed that text and tune are difficult to separate. Data collected in the patient, however, suggest some independence between text and music in songs. Moreover, the usual asymmetry in favor of text was much reduced when later verses were used. Overall, the results are interpreted as revealing strong association, not integration, between the musical and the verbal component of familiar songs.

Locating and enumerating endangered humpback whales in the eastern Caribbean with directional (DIFAR) sonobuoys

Visual surveys for whales are limited by visibility conditions at sea and whale diving behavior. Male humpback whales (Megaptera novaeangliae) sing complex ‘‘songs’’ during their winter breeding season, and low-frequency song components lend themselves to acoustic detection. A visual and acoustic survey was conducted during the peak breeding season to evaluate passive acoustic methods to assess endangered humpback whales in the Eastern Caribbean, a region where they were exploited to depletion. Directional (DIFAR) sonobuoys were used to detect singing whales. Bearing angles from the sonobuoys to singing whales were calculated in real-time, and locations determined by crossing two or more bearings. A total of 4331 km of ‘‘on-effort’’ visual survey resulted in 9 whale sightings compared to 74 acoustic detections. Acoustic detections from 350 h of monitoring resulted in an abundance estimate of 116 (95% CI: 72 293) whales in February, and 123 (95% CI: 77 313) whales in March. The paucity of visual sightings is attributed to the prevailing high winds and the brief periods that whales spend at the surface. These results demonstrate the advantage of acoustic survey methods over visual methods for detecting whales in areas with poor visibility conditions such as the Eastern Caribbean.

Male calling song provides a reliable signal of immune function in a cricket.

A critical prediction of the immunocompetence handicap hypothesis is that the expression of secondary sexual traits should be positively correlated with pathogen resistance ability This correlation is necessary if females are to be able to use a particular sexual trait as an indicator of a male's resistance ability. In this study we document a positive correlation between a sexually selected component of the calling song of male house crickets (the number of syllables per chirp) and haemocyte load, an important determinant of the ability to encapsulate pathogens in insects. The results indicate that, by favouring males which produce more syllables per chirp, females may also select males with higher pathogen resistance ability, potentially generating either direct or indirect selection on female mating preferences.

Perceptual classification based on the component structure of song in European starlings.

The ability to recognize individuals based on their vocalizations is common among many species of songbirds. Examining the psychological and neural basis of this functionally relevant behavior can provide insight into the perceptual processing of acoustically complex, real-world, communication signals. In one species of songbird, European starlings (Sturnus vulgaris), males sing long and acoustically complex songs composed of small stereotyped note clusters called motifs. Previous studies demonstrate that starlings are capable of individual vocal recognition, and suggest that vocal recognition results from the association of specific motifs with specific individuals. The present study tests this possibility by examining how variation among the motifs that comprise a song affect its discrimination and classification. Starlings were trained, using operant techniques, to associate multiple songs from a single male starling with one response, and songs from four other male starlings with another response. The level of stimulus control exerted by motif variation was then measured by having subjects classify three sets of novel song bouts in which motifs from the training songs were systematically recombined. The results demonstrate a significant, and approximately linear, relationship between song classification and the relative proportions of familiar motifs from different singers that compose a bout. The results also indicate that the motif proportion effects on song classification are primary to retroactive interference in the recall for specific motifs, and independent of any biases due to the syntactic organization of motifs within a bout. Together, the results of this study suggest that starlings organize the complex vocalizations of conspecifics by memorizing large numbers of unique song components (i.e., motifs) that are then associated with different classes. Because individual starlings tend to possess unique motif repertoires, it is likely that under natural conditions such classes will correspond to individual identity. Thus, it is likely that perceptual processing mechanisms similar to those described by the results of the present study form the basis for individual vocal recognition in starlings.

GENETIC VARIATION IN CRICKET CALLING SONG ACROSS A HYBRID ZONE BETWEEN TWO SIBLING SPECIES.

The sibling ground crickets Allonemobius fasciatus and A. socius meet along a mosaic hybrid zone at ≈ 40°N latitude in eastern North America. In this paper we report the findings of a genetic analysis of calling-song variation within and among six cricket populations sampled along a transect through the hybrid zone in southern New Jersey. We compared aspects of the calling song of both wild-caught and laboratory-reared crickets to test the hypothesis that population differences in song observed in the wild were genetically based. We found significant, species-level differences in all aspects of the calling song, and these differences persisted even after a generation of common-garden rearing in the laboratory, supporting the hypothesis that interspecific variation observed in the wild largely reflects genetic differentiation between the two taxa. A discriminant function analysis indicated that individual crickets could be assigned to the proper taxon with less than 10% error, supporting the premise that calling song could be used by female crickets as a mechanism for species recognition. One population, collected from within the hybrid zone and containing significant numbers of hybrid individuals, was intermediate in its calling song, presumably reflecting this population's mixed genetic makeup. In this hybrid zone population, song phenotype was highly correlated to a hybrid index score generated using species-specific alleles at four diagnostic allozyme markers, suggesting a multigenic basis to calling-song variation in these crickets as well as linkage disequilibrium between markers and song. Based on an analysis of laboratory-reared full-sib families, broad-sense heritabilities for calling-song characteristics were generally significant in the two A. socius populations, whereas many components of song showed no significant family effects in the three A. fasciatus populations. The genotypically mixed, hybrid zone population showed very high heritabilities for most calling-song components, which likely reflect the influence of interspecific gene flow on genetic variation for quantitative traits.

Recognition of Neighbors' Song in a Species with Large and Complex Song Repertoires: The Thrush Nightingale

To investigate aspects of neighbor recognition in a migratory bird with large and complex song repertoires we conducted playback experiments in the field with male territorial Thrush Nightingales Luscinia luscinia as subjects. Males sing with immediate variety and neighbors can share a considerable part of their repertoire of song components and song types. Subjects responded significantly more to their neighbors' song broadcast from the unshared (opposite) territorial boundary than to playback of the same song broadcast from the shared territorial boundary. Thus, this study did not detect constraints on neighbor recognition imposed for instance by large and complex song repertoires, high singing versatility, or sharing of song patterns. Because Thrush Nightingales sing shared patterns in different ways, either by constructing different song types out of the shared pool of elements or by singing shared song types in different sequential order, they could attend to song components and their syntactical arrangement, full songs, or their sequential delivery for neighbor recognition. Which mechanism they use might depend on the similarity of the song and singing style of a singer compared to other familiar conspecifics.

The Role of Linguistic Dominance in the Acquisition of Song

There is a growing body of evidence to suggest that there is a developmental sequence in children's singing, with certain singing behaviours having developmental primacy over others. The research literature indicates that, when learning songs, children first focus on the linguistic features, then rhythm, and finally the pitch and melodic attributes. This theorised hierarchy was examined as part of a larger study of singing development in early childhood in which a longitudinal sample (n=184) were assessed on a variety of vocal pitch matching tasks during each year of their first three years at school, i.e. at age five, six and seven years. In each year of testing, the assessment protocol embraced a specially-designed test battery and two sample songs. The protocol was constructed so that the test battery items (pitch glides, pitch patterns and single pitches) were deconstructed features of the two test songs, thus enabling an analysis to be made of the effects of the task on vocal pitch matching performance. The results suggest that children enter school with a clear disposition towards learning the words of the songs. In general, this ability is not matched by an ability to learn and reproduce the melodic components of the test songs. It is only in the third year of schooling that vocal pitch matching in song singing improves, but this particular ability is still significantly less well developed than that for learning and reproducing the words. 'For singers are given honour and respect by all people on the earth, since the Muse has taught them their songs, and she loves the race of singers' (Homer Odyssey) 1

Short-Range and Long-Range Songs: Use of Two Acoustically Distinct Song Classes by Dark-Eyed Juncos

-Communication signals can be divided into two functional classes: longrange signals and short-range signals. The study of bird song has concentrated almost exclusively on long-range songs. Because bird song often is used as a model system for studying learning, mate choice, and territoriality, this lack of attention to short-range songs may have misrepresented our understanding of communication systems. Short-range songs are expected to differ acoustically and functionally from those broadcast over long distances. Male Dark-eyed Juncos (Junco hyemalis) produce two classes of song that appear to function as long-range and short-range signals, respectively. These two classes differ markedly in frequency and syntax as well as in repertoire size. In terms of use, rates of short-range song production were highest in conjunction with courtship displays, when males were within close proximity to fertile mates, and during interactions with other males. In contrast, production of long-range song was not associated with courtship displays, did not vary significantly with the reproductive state of females, and was produced when males were relatively far from conspecifics. Received 5 May 1997, accepted 8 September 1997. THE TYPES OF SIGNALS USED in communication can be separated into two classes: those used over long distances and those used over short distances. These two classes represent ends of a continuum of signals that function over many different distances. Long-range signals are conspicuous, broadcast signals that often function as advertisements of territorial and reproductive status (Krebs et al. 1978, Clutton-Brock and Albon 1979). In contrast, shortrange signals often are inconspicuous and characteristically are directed at specific individuals that are within close proximity to the signaler (Wiley and Richards 1982, Smith 1991, McGregor and Dabelsteen 1996). The structure and function of avian vocalizations have been well studied. In particular, bird song has been categorized extensively and is thought to function mainly in territorial defense, mate attraction, and pair-bond maintenance (Kroodsma and Byers 1991). The study of bird song in turn has contributed greatly to our understanding of development and reproductive biology (Slater 1989, Marler 1990, Baptista and Gaunt 1994). A key factor in the success of these studies is the conspicuous nature of the signals involved. Some types of short' Present address: Department of Fisheries and Wildlife Sciences, Cheatham Hall, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA. E-mail: rtitus@indiana.edu distance vocalizations, such as those used in parent-offspring communication, have been well studied (Beecher 1990), but most of the work on avian vocalizations has focused on high-amplitude, long-range songs (LRS; Catchpole 1982, Wiley and Richards 1982, Smith 1996). Although many workers recognize that birds produce short-range songs (SRS) that function over shorter distances, the emphasis on LRS may under-represent the importance of vocal communication by only partially addressing the range of songs produced. The structure of LRS is constrained by environmental degradation, which limits the variety of sounds used to those that can be effectively transmitted across territories (Wiley and Richards 1982, Brown and Handford 1996, McGregor and Dabelsteen 1996). Songs transmitted over short distances should be less constrained by environmental degradation (Wiley and Richards 1982). The more complex structure of some SRS may facilitate their transmission specifically to intended receivers (McGregor and Dabelsteen 1996). A few studies have found components within the same songs that appear to be adapted for longand shortrange functions. Among Brown-headed Cowbirds (Molothrus ater), King et al. (1981) found that a small reduction (3 dB) in the signal-tonoise ratio decreased female response to playback by 50%. Other song components were

Wing-beat frequency mutants and courtship behavior in Drosophila melanogaster males.

Flightless mutations that affect wing-beat frequency (WBF) of Drosophila melanogaster were examined for their effect on male courtship. WBFs were measured using a fixed-wire tether that completely supports the fly in an attitude similar to hovering flight. The two spontaneous mutations, one of which reduces WBF to one-half normal and the other to zero, were placed on an isogenic background and were compared to an isogenic wildtype strain and to a genetically heterogeneous wildtype strain. Time to mating under noncompetitive conditions (single pair matings) was not significantly different among the four male types in one experiment. In a second experiment, although the time to mating varied significantly among the four male types, there was no association between the WBF that was characteristic of a male type and the length of time to mating. Time to mating was not significantly correlated with WBF, wing size, or body mass in either experiment. Genetically heterogeneous wild-type females were significantly more receptive (had shorter times to mating) than inbred wild-type females toward all four male types. During the time-to-mating tests, all four male types appeared to show typical courtship behaviors. Therefore, the male types were compared for possible differences in four components of the male courtship song: sine song frequency, interpulse interval, intrapulse frequency (= carrier frequency), and wing cycles per pulse. One or another of these components showed significant differences among the four male types (e.g., genetically heterogeneous, wild-type males showed a significantly higher sine song frequency and intrapulse frequency than males of the three isogenic types). However, the average values for all four male types were within reported wild-type ranges for each courtship song component. Although the two mutations drastically reduce WBF during tethered flight, they do not have any similar major effect on courtship. Apparently they affect muscles or neuronal control mechanisms that are not common elements shared by the wing movement of flight and male courtship song.

A genetic screen for mutations that disrupt an auditory response in Drosophila melanogaster.

Hearing is one of the last sensory modalities to be subjected to genetic analysis in Drosophila melanogaster. We describe a behavioral assay for auditory function involving courtship among groups of males triggered by the pulse component of the courtship song. In a mutagenesis screen for mutations that disrupt the auditory response, we have recovered 15 mutations that either reduce or abolish this response. Mutant audiograms indicate that seven mutants reduced the amplitude of the response at all intensities. Another seven abolished the response altogether. The other mutant, 5L3, responded only at high sound intensities, indicating that the threshold was shifted in this mutant. Six mutants were characterized in greater detail. 5L3 had a general courtship defect; courtship of females by 5L3 males also was affected strongly. 5P1 males courted females normally but had reduced success at copulation. 5P1 and 5N18 showed a significant decrement in olfactory response, indicating that the defects in these mutations are not specific to the auditory pathway. Two other mutants, 5M8 and 5N30, produced amotile sperm although in 5N30 this phenotype was genetically separable from the auditory phenotype. Finally, a new adult circling behavior phenotype, the pirouette phenotype, associated with massive neurodegeneration in the brain, was discovered in two mutants, 5G10 and 5N18. This study provides the basis for a genetic and molecular dissection of auditory mechanosensation and auditory behavior.

Substrate Vibration as a Component of a Calling Song

Substrate Vibration as a Component of a Calling Song