Abstract
Studies of avian vocal dialects commonly find evidence of geographic and acoustic stability in the face of substantial gene flow between dialects. The vocal imitation and reduced dispersal hypotheses are alternatives to explain this mismatch between vocal and genetic variation. We experimentally simulated dispersal in the yellow-naped amazon (Amazona auropalliata) by moving individuals within and across dialect boundaries in Costa Rica. One juvenile translocated across dialect boundaries altered its contact call to imitate the acoustic form of the local call six weeks post-release. In contrast, four adults translocated across dialect boundaries returned to their original capture site within 120 days, while five cross-dialect translocated adults who remained at the release site did not alter their contact calls. Translocated individuals were observed to show some segregation from resident flocks. The observation of vocal imitation by the juvenile bird supports the vocal imitation, whereas the behavior of adults is more consistent with the reduced dispersal hypotheses. Taken together, our results suggest that both post-dispersal learning by juveniles and high philopatry in adults could explain the stability of vocal dialects in the face of immigration and gene flow.
Highlights
Vocal dialects are a common manifestation of vocal learning, in which variation in calls or songs is much lower within than between geographic regions
We present the first experimental study suggesting that these mechanisms could act in concert for dialect maintenance and further that each mechanism may be age-class related
This study provides direct evidence consistent with the vocal imitation hypothesis for dialect maintenance
Summary
Vocal dialects are a common manifestation of vocal learning, in which variation in calls or songs is much lower within than between geographic regions. Cultural evolution theory predicts that dialects may change through learning errors and introduction of new call variants by immigrants [3], evidence of long-term stability of geographic boundaries and acoustic structure has been found for a number of species [4,5,6]. The vocal imitation hypothesis states that immigrants imitate the local call type upon arrival to a new dialect to facilitate interactions with new social groups [7,8] These hypotheses predict different patterns of a) post-dispersal vocal learning, b) genetic differentiation between dialects, c) cross-dialect dispersal, and d) fitness costs during social integration [7]. The vocal imitation hypothesis predicts the converse, namely that crossdialect immigration will occur, immigrants will show vocal imitation post-dispersal, limited fitness costs for immigrants during social integration, and genetic homogenization of dialects
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