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Cultural Evolution in the Eurasian Tree Sparrow: Divergence between Introduced and Ancestral Populations
Anthony L. Lang and Jon C. Barlow
Vol. 99, No. 2 (May, 1997), pp. 413-423
Published by: Cooper Ornithological Society
Stable URL: http://www.jstor.org/stable/1369948
Page Count: 11
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We investigated cultural evolution in the song of the introduced North American population of the Eurasian Tree Sparrow (Passer montanus), derived from 12 pairs brought from Germany in 1870. These birds were liberated at St. Louis, Missouri, and spread into Illinois. Cultural evolution is described here in terms of the processes of population differentiation where the song meme was the unit of transmission. The distribution of song syllable memes in each meme pool fit a null hypothesis of a neutral model with an equilibrium between mutation, migration, and drift, indicating that the memes are functionally equivalent. The introduced and ancestral (German) populations showed marked divergence in the level of meme sharing. The small size of the founding North American population, the loss of genetic diversity there, and the relative susceptibility of meme pools to founder effects suggest that much of the reduction in sharing of syllable types occurred during the founding event. Because memes also are susceptible to extinction due to drift, memes were probably lost in both populations as a result of random memetic drift. Meme diversity in Illinois was comparable with that in Germany, suggesting a large mutational input into the former population following its founding. Estimates of mutational divergence based on the frequencies of song memes in meme pools showed more population structure in Illinois than in Germany. There also was less meme flow among meme pools in Illinois than in Germany. These results suggest that there were a series of founding events during the colonization of North America.
The Condor © 1997 Cooper Ornithological Society