The Condor 99:413-423 0 The Cooper Omitholog~cal Soaety 1997 CULTURAL EVOLUTION IN THE EURASIAN TREE SPARROW DIVERGENCE BETWEEN INTRODUCED AND ANCESTRAL POPULATIONS ’ ANTHONY L. LANG* AND JON C. BARLOW Departmentof Zoology, Universityof Toronto, 25 Harbord St., Toronto, Ontario, Canada, M5S 3G5 und Centrefor Biodiversityand ConservationBiology, Royal Ontario Museum, IO0 Queens’ Park Cres., Toronto, Ontario, Canada, M5S 2C6, e-mail: [email protected] Abstract. We investigatedcultural evolution in the song of the introducedNorth Amer- ican population of the Eurasian Tree Sparrow (Passer montanus),derived from 12 pairs broughtfrom Germany in 1870. These birds were liberatedat St. Louis, Missouri, and spread into Illinois. Cultural evolution is described here in terms of the processesof population differentiation where the song meme was the unit of transmission.The distributionof song syllable memes in each meme pool fit a null hypothesisof a neutral model with an equilib- rium between mutation, migration, and drift, indicating that the memes are functionally equivalent. The introduced and ancestral(German) populationsshowed 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 susceptibilityof meme pools to founder effects suggestthat much of the reduction in sharing of syllable types occurred during the founding event. Becausememes also are susceptibleto extinction due to drift, memes were probably lost in both populations as a result of random memetic drift. Meme diversity in Illinois was comparablewith that in Germany, suggestinga large mutational input into the former population following its founding. Estimatesof 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. Key words: Eurasian Tree Sparrow, Passermontanus, song, cultural evolution,memetic diffeientiation. INTRODUCTION Populations introduced by humans are of in- Studies of population differentiation often at- terest to students of evolutionary biology be- tempt to determine the relative importance of the cause they are isolated from the homogenizing various forces that cause and prevent population effect of the flow of genetic and cultural traits divergence. There is considerable interest in de- from the parent population. Because the date of termining the genetic importance of one of these introduction, the size, and the origin of such forces in particular: founder effects and their as- populations often are precisely known, infer- sociated bottlenecks and drift. Theory suggests ences also can be made about the impact of mi- that bottlenecks affect pools of cultural traits in croevolutionary forces on these populations. Al- ways that are analogous to their effects on gene though such introductions are relatively recent, pools (Mundinger 1980, Cavalli-Sforza and high rates of cultural mutation allow cultural Feldman 1981, Lynch and Baker 1993). In fact, evolution to proceed even over short time inter- bottlenecks often have been suggested as the vals (Jenkins 1978, Ince et al. 1980, Lynch et cause of macrogeographicvariation in bird song al. 1989). To date, few studies have examined (Thielcke 1973, Baptista and Johnson 1982, differentiation in song between introduced and Lynch and Baker 1994). However, bottlenecks parental populations of birds (Jenkins and Baker in bird song rarely have been documented in nat- 1984). ural populations (Baker and Jenkins 1987). The Eurasian Tree Sparrow Passer montanus (hereafter referred to as Tree Sparrow) is an ide- al organism with which to study the applicability ’ ’ Received 10 June 1996. Accepted 21 January of models of cultural evolution to bird song. 1997. ZCurrent address:5 Massey Square,Suite 2016, To- This species is native to much of Europe and ronto, Ontario, Canada, M4C 5L6, e-mail: Asia, and was introduced into North America [email protected] when 12 pairs from Germany were released on 14131 414 ANTHONY L. LANG AND JON C. BARLOW 25 April 1870 at Lafayette Park, St. Louis, Mis- and Barlow 1987). The Tree Sparrow is semi- souri (Widmann 1889, Phillips 1928). The small colonial (Summers-Smith 1988) and the territory size of the founding population suggeststhat a defended by males is limited to the nest hole strong potential existed for founder effects to in- (Lang, unpubl. data). The nest-site song is used fluence this population. This hypothesis is sup- only in mate attraction. Males use a visual dis- ported by St. Louis and Barlow (1988) who play (termed Kopfhoch-Drohen or head-up found a reduction in genetic variation in the in- threatening by Deckert 1962) rather than vocal- troduced population. izations to repel other males that venture too Lang and Barlow (1987) discussed evidence close to the nest hole (Lang, unpubl. data). for song learning in the Tree Sparrow and in the House Sparrow (P. domesticus). Cultural trans- SAMPLING mission of song in the Tree Sparrow also is sug- Tree Sparrow nest-site songs were recorded in gested by the extensive variation found in song the breeding season from April to July 1985 in elements among the repertoires of individual Illinois near White Hall, Greene County (WH), males and populations of Tree Sparrows (Lang Beverly, Adams County (BV), Meredosia, Mor- and Barlow 1987). Although cultural transmis- gan County (ME), and Jacksonville, Morgan sion of song has not been studied in detail in the County (JA) (see Lang and Barlow 1987), and Tree Sparrow, studies of a variety of species of in 1987 near Brussels, Calhoun County (BF), oscineshave shown that song elements are faith- Loami, Sangamon County (LO), Industry and fully transmitted acrossgenerations, despite oc- Fandon, McDonough County (MC), Havana, casional mutations (Jenkins 1978, Payne et al. Mason County (HV), and again near Beverly, 1988, Trainer 1989). Adams County (Fig. 1). In Germany, songswere In this report, we test the fit of the distribution recordedin 1986 near Bockenem, Niedersachsen of Tree Sparrow song elements to a null model (NS), in Stuttgart (SG) and near Karlsruhe (KA) in which song elements are selectively neutral in Baden-Wtirttemberg, and in 1988 near Haub- and their distribution is due to an equilibrium ersbronn, Baden-Wtirttemberg (HA), and again among mutation, migration, and drift. We also near Bockenem, Niedersachsen (Fig. 1). An ex- describe the pattern of cultural differentiation tensive sampling regime was followed in which that has developed between song pools of the efforts were made to sample the songs of as introduced North American and ancestral Ger- many localities as possible and to sample as man populations. We present data on song syl- large a portion of the songs of each locality as lable sharing, flow, and diversity in the two pop- possible. Therefore, the songs of many males ulations that, given the history of the introduced were taped at each locality. Because males use population, are consistent with the influence of progressively smaller repertoires as their nesting founder effects, drift, and frequent mutations. cycles progress (Lang, unpubl. data), there is MATERIALS AND METHODS large variation in the repertoire sizes obtained from individual males (with a mean of approx- SONG STRUCTURE imately 10 syllable types). However, we as- The Tree Sparrow is a continuous singer (sensu sumed that the distribution of large and small Hartshome 1956). We follow our original de- repertoires was randomly distributed among scription of the structure of the song of this spe- samples obtained from the 12 localities. The cies (Lang and Barlow 1987) in giving the term date of sampling did not affect the distribution syllable to the song elements that make up its of repertoire sizes from each locality because continuous song. While singing, male Tree Spar- Tree Sparrows raise two to three broods per rows group syllables into bouts that last as long breeding season in North America (Anderson as 10 min. Our operational definition of a bout 1978) and males in the early stageof the nesting is a group of syllables separatedfrom adjacent cycle are present throughout the breeding sea- groups by a time interval of greater than 2.5 set son. Singing males were tape recorded until well (Lang and Barlow 1987). Each male has a rep- after they began to repeat syllable types used in ertoire of as many as 54 distinct syllable types earlier song bouts. Sample sizes are given in Ta- that it uses in the nest-site song. Many of these ble 1. Recordings were made with a Uher 4000 syllable types are sharedwith other males (Lang Report IC tape recorder set at a tape speed of CULTURAL EVOLUTION IN THE EURASIAN TREE SPARROW 415 ILLINOIS GERMANY U.S. RANGE 0 200 km FIGURE 1. Map showing sampling localities. See text for explanation of acronyms. 19 cm set-l or a Sony WM-D6C tape recorder with a Dan Gibson P-200 parabolic microphone. ANALYSIS AND DEFINITIONS TABLE 1. Number of birds tape recorded, syllables, Audiospectrograms of songs were made using a syllable types, and private syllable types by locality Kay Elemetrics Sona-Graph 7800 using a wide- and population. band (300 Hz) setting and a frequency range of 80-8,000 Hz, a Unigon FFT Spectrum Analyzer, NO. NO. private and a Kay 7900 printer or a Kay DSP Sona- NO. Total no. syllable syllable Locality birds syllables types types Graph 5500 and Kay 5510 printer. Germany The sharing of syllable types among samples NS 44 380 203 78 served as the basis for assessing the cultural di- KA 57 430 179 66 vergence of the introduced North American pop- SG 58 536 204 68 ulation from the German population. Lang clas- HA 33 327 158 65 sified syllables into syllable types by visual as- Total 192 1,673 503” 360b sessmentof their similarity (Marler and Pickert Illinois 1984, Slater et al.