Dialect Populations Research Articles

The Response of Corn Buntings to Playback of Dialects

Abstract and SummaryThe response to playback of three different dialects by 10 territorial male corn buntings was investigated; the dialects played were own dialect, the dialect of a neighbouring population (NEAR) and a dialect from 40 km away (FAR). A significant effect of dialects was found for two measures of response, latency and singing rate. Response strength varies in the pattern OWN > NEAR > FAR for these measures. This pattern of response would not maintain the observed homogeneity of dialect populations. The results are similar to those obtained by experiments on other dialect species.

ALLOZYME FREQUENCIES IN A LINEAR SERIES OF SONG DIALECT POPULATIONS.

Evaluating the biological consequences of avian song dialects is important in at least two ways. First, where appropriate experimental evidence is available, we know that dialect markers in song are learned (Marler, 1970; Marler and Mundinger, 1971). Dialect systems thus offer an opportunity to determine if and how culturally transmitted vocal signals, a fundamental feature of many songbird societies, influence patterns of gene flow. Second, despite much fine descriptive work, few attempts have been made to connect the field of behavioral research on song dialects to that of evolutionary genetics. The central issue is whether or not population specific vocal signals (dialects) cause mating to take place primarily among members of the same dialect population. This question does not specify any particular behavioral mechanism that might be hypothesized nor should it suggest that gene migration is an all-or-none phenomenon. Gene flow between adjacent dialects may vary in amount or direction depending upon such possible influences as dialect discrimination affecting mate selection, recency of contact of the populations (Remington, 1968), availability of unoccupied breeding habitat, or major environmental disturbances. If song dialects reduce gene migration among dialect populations, however, then it is reasonable to predict that neighboring dialect populations may exhibit genetic differences (Templeton, 1980a). The divergence may occur because of founder effect, genetic drift, or because of selective differences in occupied habitats as when, for example, dialects occur along an environmental gradient (Endler, 1977). differential coadaptation of genomes may also be involved. Possible outcomes of the interaction of gene flow, environmental gradients, magnitude of selection pressures, and population size have only recently begun to yield to theoretical analysis (Endler, 1977; Slatkin, 1978; Lande, 1980) and we hope that our studies may be of some use in this regard. Our field data, while not constituting a test of this developing theory, may serve to underscore the significance of gene flow in population differentiation. The four song dialect populations of Whitecrowned Sparrows treated here extend over a total of only 35 km distance in an environment of apparent homogeneity in climate and vegetation. In view of the potentially high vagility of these birds, the possible consequences of discontinuities in gene flow caused by social structure may be more easily discovered. In this report we provide allozyme frequency data from four dialect populations occurring in a linear sequence along the central California coast. From these data we describe the nature and extent of genetic differentiation within and among the four song dialect populations to test the hypothesis of genetic differentiation of dialects.

Allozyme Frequencies in a Linear Series of Song Dialect Populations

Allozyme Frequencies in a Linear Series of Song Dialect Populations

Vocal Dialect Recognition and Population Genetic Consequences

SYNOPSIS. On the basis of male territorial song, a system of discrete dialects is described in a population of White-crowned Sparrows in central, coastal California. Four of these dialects are genetically differentiated from one another. Inbreeding coefficients calculated from electrophoretic alleles indicate that individuals in a dialect are inbred due to isolation of the dialect not because of inbreeding with close relatives. Males react more aggressively to male song from an adjacent dialect than to song from another member of their own dialect but react only weakly to song from a distant dialect. This indicates that male-male interactions may have a role in maintaining dialect populations. Females of the Mountain White-crowned Sparrow have been tested in dialect experiments in the laboratory and found to respond with precopulatory sexual posturing almost exclusively to song from the home dialect in comparison to song from an alien dialect. This indicates that female choice of mate may also play a role in maintaining dialect populations.

Early Experience Determines Song Dialect Responsiveness of Female Sparrows

In a laboratory experiment, female white-crowned sparrows responded almost exclusively to male songs taken from their home dialect region and usually not to songs taken from an alien dialect region. Song dialect populations may represent a level of genetic population structure below that of the subspecies and may play an important role in songbird evolution.

Effective population size in a songbird: some possible implications

Song dialects in White-crowned Sparrows (Zonotrichia ieucophrys nuttalli) may act as partial barriers to the free exchange of genes. Within a dialect population, a genetic neighbourhood comprises about 100 individuals. Other factors combine to reduce the effective number to less than 50. By Wright’s methods, the genetic divergence among subpopulations (Fst) expected in a population exhibiting this size effective number with neutral alleles is about an order of magnitude larger than the observed Fst calculated from electrophoretically detectable alleles. Natural selection may therefore be maintaining greater homogeneity within a dialect than expected by assuming that alleles are neutral. From the torus model of Maruyama, however, the expected Fst values are close to those observed, suggesting no major departures from panmixia within dialect populations. The degree of genetic isolation exhibited between dialect populations may provide an explanation for the more rapid rate of speciation in passerine birds.

SONG DIALECTS AND GENETIC DIFFERENCES IN WHITE-CROWNED SPARROWS (ZONOTRICHIA LEUCOPHRYS).

Song dialects have been described in several bird species (Marler and Tamura, 1962; Lemon, 1966; Nottebohm, 1969). Clear examples are found in the resident white-crowned sparrows (Zonotrichia leucophrys nuttalli) of coastal California and in populations of the chingolo (Zonotrichia capensis) of Argentina. Where dialects occur in these species an area of breeding habitat is occupied by territorial males that with few exceptions sing a very similar song. Contiguous and allopatric with this area males of another population sing a different song type. It has been shown (Marler and Tamura, 1964; Marler, 1970) that in the white-crown (Z. 1. nuttalli) the dialect is learned during the first few weeks of life. The contiguity of the populations with discretely different vocalizations could be related to several interesting questions in population genetics, vocal communication, and evolutionary processes. On a general level, however, the dialect phenomenon leads to two central issues: (1) How do dialects arise? and (2) What role, if any, do they play in the biology of the birds? In this paper I provide a speculation on the first question and some data that may clarify the second. Following a suggestion by Marler and Tamura (1962), Nottebohm (1969) proposed that females might preferentially mate with males of their own dialect, thereby constraining a locally adapted gene pool. This hypothesis, that dialects reduce gene migration, came from the observation that Z. capensis on altitudinal gradients in Argentina exhibits a series of dialect populations possibly corresponding to different selective regimes, whereas a single dialect is found over vast areas of lowland pampas where selection may be spatially homogeneous (Nottebohm, 1969; Nottebohm and Selander, 1972). There, are other possible explanations of song dialects in birds. First, song dialects, a consequence of vocal learning, may play no important role. Perhaps during the early learning phase, young birds acquire population specific calls that promote flocking, foraging efficiency, predator avoidance, or individual recognition, that are important for winter survival. Thus, the selective advantage of vocal learning would be explained by winter ecological conditions and not territorial breeding behavior. Second, dialects could maximize outcrossing in small populations. Females would mate with males having a song type unlike that of their early experience. Third, dialects may be a result of intrasexual selection and bear no direct relationship to mate selection. Perhaps vocal convergence bestows some advantage in gaining and holding a territory but females do not use dialect information for mate choice. Using an electrophoretic analysis of alloenzymes, I investigated populations of Nuttall's white-crowned sparrow (Z. 1. nuttalli) in California and populations of the mountain white-crown (Z. 1. oriantha) in Colorado to determine if song dialects were correlated with genetic differentiation.