Abstract
Learned bird songs are often characterized by a high degree of variation between individuals and sometimes between populations, while at the same time maintaining species specificity. The evolution of such songs depends on the balance between plasticity and constraints. Captive populations provide an opportunity to examine signal variation and differentiation in detail, so we analyzed adult male zebra finch (Taeniopygia guttata) songs recorded from 13 populations across the world, including one sample of songs from wild-caught males in their native Australia. Cluster analysis suggested some, albeit limited, evidence that zebra finch song units belonged to universal, species-wide categories, linked to restrictions in vocal production and non-song parts of the vocal repertoire. Across populations, songs also showed some syntactical structure, although any song unit could be placed anywhere within the song. On the other hand, there was a statistically significant differentiation between populations, but the effect size was very small, and its communicative significance dubious. Our results suggest that variation in zebra finch songs within a population is largely determined by species-wide constraints rather than population-specific features. Although captive zebra finch populations have been sufficiently isolated to allow them to genetically diverge, there does not appear to have been any divergence in the genetically determined constraints that underlie song learning. Perhaps more surprising is the lack of locally diverged cultural traditions. Zebra finches serve as an example of a system where frequent learning errors may rapidly create within-population diversity, within broad phonological and syntactical constraints, and prevent the formation of long-term cultural traditions that allow populations to diverge.
Highlights
The phenotypic diversity of an animal signal reflects the way in which it develops
Population divergence in song characteristics requires that novel song types are generated frequently enough to overwhelm the homogenizing effects of the dispersal of individuals and songs between populations
Each of these two clusters clearly encompassed considerable structural diversity. This diversity did not fall into very clearly defined categories, there was weak evidence for clustering tendency and we set the threshold for the distinction of clusters at k = 10 for further analysis. Examples of these 10 clusters are shown in Figure 2B
Summary
The phenotypic diversity of an animal signal reflects the way in which it develops. Learned bird song develops from an interplay of imitative vocal learning and unlearned genetically based biases and predispositions (Catchpole and Slater, 2008). While it is clear that in songbirds both cultural transmission and genetic constraints play a role in development, their relative contributions to population differentiation remain generally unclear (Podos and Warren, 2007). The rapid tempo of cultural evolution means that novel song forms frequently arise and can quickly become established in a population. This can promote population divergence (especially in “dialect” forming species, e.g., Baptista, 1977; Podos et al, 2004). For populations that have not yet diverged in the genes underlying these predispositions, this means that song characteristics will largely overlap between populations
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