Dialect Populations Research Articles

High levels of gene flow among song dialect populations of the Puget Sound white‐crowned sparrow

AbstractPopulations within a species can show geographic variation in behavioral traits that affect mating decisions or limit dispersal. This may lead to restricted gene flow, resulting in a correlation between behavioral variation and genetic differentiation. Populations of a songbird that differ in a learned behavioral trait, their song dialects, may also differ genetically. If song dialects function as mating barriers, evolutionary processes such as genetic drift should lead to divergence in allele frequencies among dialect populations. The Puget Sound white‐crowned sparrow (Zonotrichia leucophrys pugetensis) is an excellent study system with a well‐defined series of song dialects along the Pacific Northwest coast. A previous study found low genetic differentiation based on four microsatellite loci; however, available loci and analyses techniques have since dramatically improved and allow us to reassess gene flow in this species. We also add extra samples to fill in gaps and add a new level of analysis of geographic variation. Based on acoustic similarities, we group six song dialects into two geographically larger “northern” and “southern” song themes. One southern dialect is acoustically more similar to dialects in the north, which makes the genetic profile of birds singing this dialect particularly interesting. Traditional F‐statistics, analysis of molecular variance as well as Bayesian techniques confirmed the earlier result that geographic variation in song does not correlate with the neutral genetic structure of the sampled dialect populations. The song themes also did not differ genetically, and the origin of the extralimital northern‐theme dialect cannot be determined. We compare this result to findings in several other species and discuss how the timing of learning and dispersal allow vocalizations to vary independently of patterns of genetic divergence.

Fidelity of Song Imitation and Stability of Dialect Songs in Brown-headed Cowbirds

Temporal stability in the acoustic structure of dialect songs is a critical variable for studies of cultural evolution in songbirds. Here we report that the structure of the flight whistle song of Brown-headed Cowbirds (Molothrus ater) of the Convict dialect in the eastern Sierra Nevada of California remained essentially stable over almost 30 years. Quantitative measurements showed a minor structural change in one of four syllables and a small but statistically significant increase in duration for whistles recorded in 2006 versus 1990. Audiospectrograms of whistles recorded in the late 1970s revealed no major structural differences from the 1990 and 2006 whistles. These results are consistent with field and ontogenetic studies showing that young cowbirds copy the songs of adult males with very high fidelity, although it may take them up to two years to do so. We contrast the Convict results with those from the adjacent Mammoth dialect, in which the local whistle changed substantially over approximately the same period covered by the current study (O'Loghlen et al. 2011) and discuss a possible explanation for the divergent results based on ecological differences between the two dialects. As far as we are aware, this is the first report of such contrasting results for acoustic stability in the songs of contiguous dialect populations. The stability shown by the Convict whistle is remarkable given the extreme structural variation among whistles from other dialect populations in the area and evidence of dispersal and gene flow among these local populations.

Rain-Call Dialects of the Chaffinch, Fringilla coelebs (Fringillidae), in Ukraine

Abstract Four types of Chaffinch rain-calls were found in Ukraine: “rülsch” - a trill signal widely spread in Europe; “hui” - a whistle signal that occurs in North-Western and Central Europe; “Crimean” whistle signal known only from Crimean peninsula and “Caucasian” signal occurring in Caucasus, Asia Minor and Balkans. Sonograms of rendition versions are given for all of the call types. Distribution of dialects of Chaffinch rain-calls in Ukraine was examined. “Rülsch”- dialect occurs at most of the plane Ukraine and Carpathians. Owing to colonizing artificial afforestations in steppe zone this dialect population’s range expanded southward to the coast of the Black and Azov seas. “Hui”-dialect is spread in the Lower Danube region. At the North-Eastern Danube delta Chaffinch’s with “hui”- and “rülsch”- rain-calls are found together and a bird was found that uttered both signals alternately but hybrid signals were not registered. It may attest to recent invasion by “rülsch”- population of Chaffinch’s there. “Crimean” dialect is distributed in mountainous Crimea and in most of the Crimean steppe zone. “Caucasian” rain-call renditions are registered in cases of individual vagrant birds in eastern Crimea and Lower Danube region

Cultural Evolution and Long-Term Song Stability in a Dialect Population of Brown-Headed Cowbirds

Knowing the extent to which the acoustic structure of songs is temporally stable is essential to understanding how cultural evolution affects song dialects in oscines. The acoustic structure of the most prevalent variant of the flight-whistle song recorded from male Brown-headed Cowbirds (Molothrus ater) in the Mammoth dialect (Mammoth Lakes, California) from 2005 to 2009 differed significantly and consistently from whistles recorded in 1989 and 1978–1985. The most common whistle variant in the 2005–2009 sample had structural features absent from whistles described in the earlier studies and overall was produced at a consistently lower acoustic frequency. Besides the emergence of this new variant sometime between 1989 and 2005, the prevalence of other variants of the whistle also changed from 1978 to 2009. Changes reported in other studies of cultural evolution in oscines have been based on lower-level structural elements (notes and syllables), whereas we found that entire songs appear to have evolved as cultural units or memes. We discuss possible mechanisms as to how these changes may have occurred. Despite these changes, the Mammoth whistle still retained the same basic three-syllable structure it had 31 years ago. This stability is notable because of the potential for extreme variation in whistle structure exemplified by the distinct whistles of nearby dialects in the region.

Song Dialects in the Corn Bunting (Emberiza calandra)

This paper describes the system of local dialects in the Corn Bunting in Britain. Each dialect population contains between 30 and 100 males, all males within a dialect sing the same form and number of song types. The Corn Bunting is therefore the first species for which both clear local dialects and a repertoire of song types have been described. The boundaries between dialects have remained in the same position for three years. The origin, maintenance and functional significance of dialects in this species are discussed.

Use of trace element analysis of feathers as a tool to track fine-scale dispersal in birds

Tracking dispersal and migratory movements of animals over small and large spatial scales is a challenge. In birds, a promising yet underutilized tool is the trace elemental composition of feathers. The elemental profile of a feather may reveal information about the geographic origin of a bird provided that molting occurs on the breeding grounds and that elemental differences exist between breeding areas. Here, we explore the use of trace elemental composition in body feathers of the Puget Sound white-crowned sparrow Zonotrichia leucophrys pugetensis as a tool (1) to discriminate among birds collected in four different song dialect populations along a 400-km stretch of the Pacific Northwest coast and (2) to assign males singing nonlocal dialects in one population to potential natal populations. Inductively coupled plasma mass spectrometry detected 34 trace elements in sampled feathers and in a discriminant function analysis seven of these elements differed among the four source populations. Half of the six nonlocal dialect singers, who were likely to have immigrated into the focal population, were assigned to a population that matched their song dialect. Our study suggests that feather microchemistry is a promising tool for identifying geographic origins of dispersing birds over small geographic scales and in combination with other markers, such as song, may give insight into ecological and evolutionary processes.

Song dialects do not restrict gene flow in an urban population of the orange-tufted sunbird, Nectarinia osea

Geographic variation in vocalizations is widespread in passerine birds, but its origins and maintenance remain unclear. In this study, we test the hypothesis that song dialect, a culturally transmitted trait, is related to the population genetic structure of the orange-tufted sunbird, Nectarinia osea. To address this, we compared mitochondrial DNA (mtDNA) sequence variation together with allele frequencies at five microsatellite loci from an urban population of sunbirds exhibiting two distinct song dialects on a microgeographic scale. Our findings reveal no association between dialect membership and genetic composition. All genetic measures, from both mitochondrial and nuclear DNA, indicate high levels of gene flow between both dialect populations. The low F ST values obtained from mtDNA and microsatellite analysis imply that the variation among dialects does not account for more than 2%, at best, of the overall genetic variation found in the entire population. These measures fall well within the range of similar measures obtained in other studies of species exhibiting vocal dialects, most of which fail to detect any dialect-based genetic differentiation. The persistence of dialects in the orange-tufted sunbird may thus best be explained by dispersal of individuals across dialect boundaries and possibly from surrounding areas, followed by postdispersal vocal matching. Because genetic structuring appears weaker than cultural structure in this species, we discuss the behavioral mechanisms underlying dialect maintenance in the presence of apparent gene flow.

Genetic analysis of song dialect populations in Puget Sound white-crowned sparrows

The relationship between cultural variation and biological variation among natural populations has been the subject of both theoretical and empirical study. Zonotrichia leucophrys pugetensis is one of three subspecies of white-crowned sparrow known to form geographical song dialects. We investigated whether these dialects correspond to genetic differences among Z. l. pugetensis populations. We compared allele frequencies at four microsatellite loci in males from 11 sites spanning six dialects over the subspecies’ range in Oregon and Washington. Cluster analysis and genotype assignment tests indicated no tendency for sample sites within dialect areas to be genetically more similar than are sites from different dialect areas. AMOVA tests revealed high within-site variation and low but significant cross-site and cross-dialect-area variation. Finally, genetic distance between sites was not correlated with dialect differences when the effect of geographic distance was controlled statistically. We compare our finding of low genetic differentiation among Z. l. pugetensis dialect populations to results of previous studies on Z. l. nuttalli and Z. l. oriantha. Because genetic structuring appears weaker than cultural (song dialect) structure in this species, we discuss the behavioral mechanisms underlying dialect maintenance in the presence of apparent gene flow. Key words: birdsong, cultural evolution, geographic variation, microsatellites, Zonotrichia leucophrys pugetensis. [Behav Ecol 15:636–646 (2004)]

Dialect Discrimination by Male Orange-Tufted Sunbirds (Nectarinia osea): Reactions to Own vs. Neighbor Dialects

Male orange-tufted sunbirds (Nectarinia osea) exhibit distinct song dialects throughout Israel. Recently, two distinct local dialects with a sharp boundary were discovered in a small (1.5 km 2 ) urban neighborhood densely inhabited by 63 territorial sunbird pairs. We conducted playback experiments to determine song dialect discrimination capability by sunbird males in this neighborhood. Males of both dialects responded significantly more strongly to playback of their own dialect than to that of the adjacent dialect. In spite of the extreme proximity between the two dialect areas, we found no effect of distance to the neighboring dialect on the intensity of any the behavioral responses. We suggest that due to the complex acoustic properties of this urban neighborhood, sunbirds are extremely limited in the number of neighboring males they can assess to establish what the local song is. A stronger response to one’s own dialect is therefore expected, and we discuss how local dialects could be maintained via this mechanism regardless of the very small distances between territories and dialect populations.

MICROGEOGRAPHIC SONG DIALECTS IN THE ORANGE-TUFTED SUNBIRD (NECTARINIA OSEA)

Abstract In a study of male song in the orange-tufted sunbird (Nectarinia osea) in an urban neighborhood in Ramat-Aviv, Israel, we discovered the occurrence of song variation on a microgeographic scale in the form of two distinct dialects with a sharp boundary between them. The main distinction between the two song dialects is the frequency of the trill, which comprises the terminal part of the song. A large difference of 2-3 kHz in the peak frequency of the trill was discovered between the two dialects, which could be easily distinguished by ear. Thirtyseven males were recorded singing the 'low' dialect and 21 birds sang the 'high' dialect. Four other birds sang both dialects or 'hybrid' songs. Along the boundary that separated the two dialect populations, neighboring birds sang different dialect songs, although they were only 20-30 meters apart. All four 'bilingual' birds occupied territories near the dialect boundary. The historical processes leading to the formation of this dialect system may result from the pattern of human settlement at the time of the establishment of this neighborhood in the early 1950's. The spatial distribution of the two sunbird dialect populations, and the apparent low dispersal rates of birds from their natal dialect area, suggest the existence of a mechanism, which currently maintains these dialects at the current boundaries.

Songs and Sexual Responses of Female White-Crowned Sparrows (Zonotrichia Leucophrys) From a Mixed-Dialect Population

Abstract Some researchers have suggested that female songbirds mate with males singing local song types in preference to males singing dialects from more distant populations. Such behaviour might promote genetic isolation among dialect populations. We studied captive female white-crowned sparrows (Zonotrichia leucophrys) from a population in which two song types were equally common, as a model for behaviour at dialect boundaries. Subjects were captured as adults, and the song type of the mate of each was known. Treated with estradiol, females gave sexual displays in response to playback of conspecific male song. As a group, they solicited no more strongly to either local song type, suggesting that males singing either local song type should be able to attract mates. Individuals solicited no more strongly to their mate's song type than to the other local song type. This suggests that strength of response of captive females to song playback may not accurately reflect the behaviour of free-living individuals. Subjects were also treated with testosterone to induce singing. Individuals sang their mates' song type more often than expected by chance. Given that female white-crowned sparrows in this population do not consistently choose mates of one song type, we develop the argument that females learn, for performance, the song type of their first mate. However, the type of song learned for performance appears unlikely to restrict their subsequent mate choice decisions. Our results suggest that female white-crowned sparrows do not base their choice of mates on dialectal variation in male song, and that it is unlikely that mate choice decisions based on song dialect promote the genetic isolation of dialect populations.

Delayed Access to Local Songs Prolongs Vocal Development in Dialect Populations of Brown-Headed Cowbirds

A recent study by O' Loghlen and Rothstein (1993) found that ontogeny of the Mammoth dialect flight whistle (FW) and repertoires of local perched songs (PS) was not complete by the first breeding season for male Brown-headed Cowbirds (Molothrus ater artemisiae) in the eastern Sierra Nevada of California. To determine how typical of the region these results were, I compared adult and yearling vocal behavior in the Convict dialect adjacent to Mammoth and the Round Valley dialect, 55 km south and 900 m lower elevation. In the Convict group, a majority of 20 yearlings produced either incomplete local (35%) or foreign (35%) IWs. In the Round Valley, 15 of 19 yearlings (79%) gave foreign whistles. In both dialects, yearling PS repertoires lacked local song types, and in Convict, repertoires were significantly smaller than those of local adults. As was found in the Mammoth dialect, incomplete FWs of yearlings were resistant to modification during the season, and modification of yearling PS repertoires was also arrested. I propose a scheme for vocal development in these Sierran populations and discuss possible reproductive consequences of delayed vocal learning

Culturally correct song dialects are correlated with male age and female song preferences in wild populations of brown-headed cowbirds

Variation in vocal behavior among local populations of songbirds may be significant to females in mate choice. In a study of dialect populations of brown-headed cowbirds, estradiol-implanted females from two dialects held the pre-copulatory lordosis posture longer in response to playback of the local flight whistle song than to foreign whistle types from adjacent and more distant dialects. Females were held in captivity for a relatively brief period prior to testing and received no tutoring so discrimination was based solely on experience in the wild. This is the first study to show evidence of discrimination by female cowbirds based on flight whistle type. Evidence is presented from one of the study dialects that the majority of yearling male cowbirds are vocally distinct from resident adults in having either foreign or incomplete local whistles. Although these yearlings are fully mature sexually, they have little or no mating success. The correlation between female whistle preference and male mating success suggests that the ability to give the correct local whistle type may be a characteristic used by females to assess age and quality of a potential mate. A learned female preference for the predominant local song type may be a factor in the stability of these dialects by making it adaptive for males to conform to the local dialect.

Song Dialect Recognition by Male White-Crowned Sparrows: Effects of Manipulated Song Components

Previous studies have shown that male White-crowned Sparrows (Zonotrichia leucophrys) discriminate among song dialects in the context of territorial behavior. We studied male response to song stimuli that differed systematically from the subjects' local dialect. We created four "hybrid" songs composed of elements from two adjacent dialects and monitored the responses of males from one dialect population to these four stimuli and to two unaltered dialect control songs. The most potent stimulus was the song from the dialect of the subjects, and the least stimulating song was that of the neighboring dialect. When we substituted the local dialect introductory components for those of the neighboring dialect, the response was as great as that given to the local dialect. Substitutions in other portions of the song caused decreased response in the subjects. Our results suggest that the vocal information controlling the territorial behavior of males in this particular dialect population is encoded in acoustic features located in the first part of the song.

Mate choice by female white-crowned sparrows in a mixed-dialect population

It has been argued that the song dialects of white-crowned sparrows, Zonotrichia leucophrys, may function to restrict gene flow between dialect populations, thus promoting adaptation to local environmental conditions. One proposed mechanism whereby this may occur is if a female mates preferentially with males singing her natal dialect, typically the song type of her father. Previous field and laboratory studies of the role played by song differences in mate choice by female white-crowned sparrows have produced equivocal results. These investigations were conducted in populations in which a single song dialect was predominant. We examined mate choice in a population in which two song dialects are equally common. We found that songs of mates of individual females in successive years were no more likely to be of the same dialect than expected by chance. In addition, individual females did not mate preferentially with males whose songs matched those of their fathers. We conclude that, in this population, females choose mates on the basis of characteristics other than song type.

Vocal Dialects and Their Possible Relation to Honest Status Signalling in the Brown-Headed Cowbird

We describe dialects in the flight whistle of the Brown-headed Cowbird and contrast previous hypotheses for the maintenance of dialects with a new one that assumes that a male's ability to give the correct local dialect is an honest signal of relatively high male quality. The three dialects upon which we focus are part of an extensive dialect system along the eastern Sierra Nevada. The dialects are partially isolated by unsuitable habitat and are unusual because they differ via lexical rather than the less extreme phonetic differences that characterize song dialects in most other species. Because males whistle just before copulating, whistles may function in mate choice. Since flight whistles are also used over long distances, we predicted and confirmed that males within the same dialect have quantitative whistle differences of potential value for individual recognition. Other quantitative analyses indicated phonetic differences among homologous whistle elements from adjacent dialects. Recordings made between 1978 and 1980 showed no quantitative or qualitative differences from a large sample of 142 males recorded between 1983 and 1985. Such temporal stability is expected since the dialects are large, being 10 to 30 km in extent and probably contain hundreds of individuals. Historical records demonstrate that the dialect populations developed since the late 1930s. Males banded in one dialect but recorded in another made up 13.0% of our adult sample and were more likely to have foreign whistles than adults banded and recorded in the same dialect. Yearling males were significantly less likely to whistle than adults, and yearlings that did whistle were significantly more likely to have foreign whistles. Thus possession of a locally appropriate whistle is a reliable indicator of a male's age which is a major correlate of male mating success and possibly of male quality, as nearly all copulations involve adult males. These age differences are consistent with our new "honest convergence" hypothesis and inconsistent with the local or genetic adaptation hypothesis which predicts that vocal ontogeny is closed by a male's first breeding season. Bilingual males and those with hybrid whistles combining elements from two dialects made up 0 to 8% of the males within dialect areas. By contrast, 38% of males in one contact zone between two dialects were bilingual and 54% of males in another contact zone gave hybrid whistles. These trends are consistent with the honest convergence hypothesis and inconsistent with hypotheses that dialects are maintained by isolation or because they contribute to local adaptation among populations.

The Biology of Bird-Song Dialects

AbstractNo single theory so far proposed gives a wholly satisfactory account of the origin and maintenance of bird-song dialects. This failure is the consequence of a weak comparative literature that precludes careful comparisons among species or studies, and of the complexity of the issues involved. Complexity arises because dialects seem to bear upon a wide range of features in the life history of bird species. We give an account of the principal issues in bird-song dialects: evolution of vocal learning, experimental findings on song ontogeny, dialect descriptions, female and male reactions to differences in dialect, and population genetics and dispersal.We present a synthetic theory of the origin and maintenance of song dialects, one that accommodates most of the different systems reported in the literature. The few data available suggest that large, regional dialect populations are genetically differentiated; this pattern is correlated with reduced dispersal between dialects, assortative mating by females, and male-male exclusion. At the same time, “subdialects” may be formed within regional dialects. Subdialect clusters are usually small and may represent vocal mimicry among a few adjacent territorial males. The relative importance of genetic and social adaptation may contribute to the emergence of subdialects; their distinctiveness may be correlated with the degree of polygyny, for example. Thus, subdialect formation is linked to one theory of the evolution of repertoire size, but data are too fragmentary to examine this idea critically.

Assortative mating by white-crowned sparrows at song dialect boundaries

We tested the hypothesis that female Nuttall's white-crowned sparrows ( Zonotrichia leucophrys nuttalli) mate assortatively with males from the same dialect population. Young birds of both sexes learn their natal dialect during an early sensitive period, and for females, this early experience may be the basis of future mate choice. A total of 32 female sparrows were mist-netted for three experiments at or near dialect boundaries just inside the Limantour, Drake and Clear dialect populations in Marin Co., California. The mates of all captured females sang the home dialect. All females were implanted with testosterone and maintained in captivity. Of the females which began to sing, 25 sang recognizable white-crowned sparrow songs. Of those 25 females, 24 had mated assortatively, thus supporting the assortative mating hypothesis.

REPLY TO "ALLOZYMES AND SONG DIALECTS: A REASSESSMENT".

Our research centers on birdsong dialects, which are culturally transmitted (learned) vocal traditions. We evaluate the influence dialects have on the population biology of the White-crowned Sparrow, Zonotrichia leucophrys. Zink and Barrowclough (1984), in this issue, criticized our recent study (Baker et al., 1982b). Our null hypothesis (Baker et al., 1 982b) was that there were no genetic differences among song dialect populations of White-crowned Sparrows in coastal California. Statistical tests on samples of allozyme loci from four dialects falsified this hypothesis. Variation in gene frequencies at eight allozyme loci revealed a relatively small amount of statistically significant heterogeneity within dialects and a substantially larger amount between dialects (Table 2, Baker et al., 1982b; in Table 1 the correct frequency of Pgma-A at CGR is .412). The results suggested reduced gene flow among dialects. We also correlated genetic distance and geographic distance among samples and dialects. Genetic distance had significant positive correlation with geographic distance between dialects but no significant correlation between samples within dialects. We concluded that . . the observed genetic isolation is caused primarily by dialects, not geographic distance. We believed isolation by distance to be of secondary importance. Zink and Barrowclough reassessed our correlations. They corrected geographic and genetic distance axes for the difference in range of values of within and between dialect samples and argued there were no significant differences in the correlation coefficients. They did not justify this approach. There is no inherent curtailment on the genetic distance axis; genetic distance values between samples within dialects are free to vary as much as values between dialects. There are two types of curtailment inherent in the geographic distance variate. In a linear series of dialects, distances between dialects average larger than distances between samples within

Dialect Discrimination by White-Crowned Sparrows: Reactions to Near and Distant Dialects

Abstract In Marin County, California, the dialect populations of Zonotrichia leucophrys nuttalli are contiguous, and there is little dialect mixing. The possible importance of male-male interactions in preventing dialect mixing was tested with song-playback experiments. Males of the Limantour dialect were presented the Limantour dialect, Drake or Buzzy dialects (neighboring), or Clear dialect (distant). From previous work, we predicted that Limantour males would respond with equal or more aggression to songs of immediately neighboring dialects in comparison with their own dialect but would respond at lower levels to a distant dialect. Instead, we found that Limantour males sang significantly more songs in response to the Limantour dialect than to either neighboring or distant dialects, although the response decreased with distance, as expected. These results led us to hypothesize that responses to an alien dialect may be influenced by (1) opportunity to habituate to the alien dialect, (2) recency of divergence of the two dialects, (3) recency of contact of the two dialects, and (4) sounds common in aggressive vocalizations in other contexts being also present in some song dialects but not others.