Effective population size in a songbird: some possible implications

Abstract

SUMMARYSong dialects in White-crowned Sparrows (Zonotrichia leucophrys nuttalli) may act as partial barriers to the tree 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 (Fr,) expected in a population exhibiting this size effective number with neutral alleles is about an order of magnitude larger than the observed F,, 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 F,, values are close to those observed, suggesting no major departures from panmixia within dialect popuiations. The degree of genetic isolation exhibited between dialect populations may provide an explanation for the more rapid rate of speciation in passerine birds.

Mitochondrial DNA Homogeneity in the Phenotypically Diverse Redpoll Finch Complex (Aves: Carduelinae: Carduelis flammea-hornemanni)

“…Assuming a balanced sex ratio and other minor assumptions (Birky et al 1983), it corresponds to a total long-term effective population size (Ne) of 100,000 to 200,000 individuals. This is one to three orders of magnitude larger than what has been previously reported for noncolonial avian species using demographic modeling (Barrowclough 1980;Baker 1981;Fleischer 1983), allozyme data (Barrowclough 1983), or cytological information (Barrowclough and Shields 1984). We suspect that the disparity is due to the different population structure of the species studied in each case, and not to the inappropriateness of the different models employed.…”

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

“…Dialects are maintained because they serve as population markers that local females use to identify and thus to preferentially mate with local males (Konishi 1965;Nottebohm 1969;Baker et al 1981aBaker 1983). Because dialects maintain locally adapted or coadapted gene complexes via assortative mating (Marler and Tamura 1962, Nottebohm 1969, Baker 1982a, they result in "excess genetic differentiation," i.e., differentiation among dialects is greater than that due solely to spatial separation (Baker 1974(Baker ,1975(Baker , 1981(Baker , 1982a(Baker , 1982b(Baker , 1983Baker et al 1982b; but see Zink and Barrowclough 1984).…”

“…The heightened success of males who transformed their songs to match local dominants may have occurred because these males were signalling honestly that they were not newcomers to the local social milieu. Most of the controversy concerning dialects has dealt with Zonotrichia spp., whose dialects have been explained in terms of deceptive convergence, isolation, and local adaptation (Baker 1974(Baker ,1975(Baker ,1981(Baker ,1982a(Baker , 1982b(Baker , 1983Baker and Cunningham 1985;Mewaldt 1978, 1981;Baker et al 1981aBaker et al , 1981bBaker et al , 1981cBaker et al , 1982aBaker et al , 1982bBaker et al , 1982cBaker et al , 1984Handford and Nottebohm 1976;Petrinovich et al 1981;Tomback et al 1983;Baptista and Petrinovich 1984;Payne 198 la;Kroodsma et al 1984;Zink and Barrowclough 1984). The Zonotrichia results may conform to the honest convergence hypothesis, but our main objective here is to test this and the other hypotheses with the cowbird dialects.…”

A COMPARISON OF THEORETICAL AND ELECTROPHORETIC ASSESSMENTS OF GENETIC STRUCTURE IN POPULATIONS OF THE HOUSE SPARROW ( PASSER DOMESTICUS )

“…These methods have been used for a variety of organisms (Kerster , 1964;Greenwood, 1974;Powell et al, 1976) and quite recently, were investigated extensively for populations of birds (Barrowclough, 1980a). Only two studies seem to have compared the two methods using data from Revised September 30, 1982 the same population (Kidd and Cavalli-Sforza, 1974;Baker, 1981).…”