Search

Funding: ECG is funded by a Royal Society University Research Fellowship (UF160081). RFL and LZ are funded by the BBSRC (BB/R008736/2). LL was supported by a Leverhulme Trust Grant to Luke Rendell (among other recipients; grant reference RPG-2013-367) Humpback whale song is an extraordinary example of vocal cultural behaviour. In northern popula-tions, the complex songs show long-lasting traditions that slowly evolve, while in the South Pacific, pe-riodic revolutions occur when songs are adopted from neighbouring populations and rapidly spread. In this species, vocal learning cannot be studied in the laboratory, learning is instead inferred from the songs’ complexity and patterns of transmission. Here, we used individual-based cultural evolutionary simulations of the entire Southern and Northern Hemisphere humpback whale populations to formalise this process of inference. We modelled processes of song mutation and patterns of contact among popu-lations and compared our model with patterns of song theme sharing measured in South Pacific popula-tions. Low levels of mutation in combination with rare population interactions were sufficient to closely fit the pattern of diversity in the South Pacific, including the distinctive pattern of West-to-East revolu-tions. Interestingly, the same learning parameters that gave rise to revolutions in the Southern Hemi-sphere simulations gave rise to evolutionary patterns of cultural evolution in the Northern Hemisphere populations. Our study demonstrates how cultural evolutionary approaches can be used to make infer-ences about the learning processes underlying cultural transmission and how they might generate emergent population-level processes. Publisher PDF

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.