Global cultural evolutionary model of humpback whale song

Abstract

Humpback whale song is an extraordinary example of vocal cultural behaviour. In northern populations, the complex songs show long-lasting traditions that slowly evolve, while in the South Pacific, periodic 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 formalize this process of inference. We modelled processes of song mutation and patterns of contact among populations and compared our model with patterns of song theme sharing measured in South Pacific populations. 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 revolutions. Interestingly, the same learning parameters that gave rise to revolutions in the Southern Hemisphere 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 inferences about the learning processes underlying cultural transmission and how they might generate emergent population-level processes. This article is part of the theme issue ‘Vocal learning in animals and humans’.

Song complexity is maintained during inter-population cultural transmission of humpback whale songs

“…This could also explain why east Australian songs as a whole tended to be more complex than New Caledonia, albeit not significantly. The role of these disparate population sizes is already hypothesized to drive the consistently eastward transmission of these songs across the South Pacific 22 , 50 , as the west Australian population is the largest and eastward populations get subsequently smaller 51 . Population size has further been shown to influence song learning in other species as well, such as the critically endangered honeyeater whose population decline is linked with a stark loss of vocal culture 52 .…”

When does cultural evolution become cumulative culture? A case study of humpback whale song

“…As controlled social learning experiments are currently unfeasible in this species, agent-based models that explicitly test social learning and cultural transmission of humpback song at the individual level have provided compelling evidence for these underlying cultural processes [ 57 , 58 ]. Extending this work to a global scale, cultural evolution models of song transmission suggest that simple learning rules can create population-level emergent properties where low levels of mutation in combination with rare population interactions match empirical song sharing patterns in the South Pacific, including the distinctive west to east pattern of revolutions [ 80 ]. This directional transmission appears driven by differences in population sizes, as hypothesized by [ 20 , 75 ]: songs spread from large to small populations [ 80 ].…”

“…Extending this work to a global scale, cultural evolution models of song transmission suggest that simple learning rules can create population-level emergent properties where low levels of mutation in combination with rare population interactions match empirical song sharing patterns in the South Pacific, including the distinctive west to east pattern of revolutions [ 80 ]. This directional transmission appears driven by differences in population sizes, as hypothesized by [ 20 , 75 ]: songs spread from large to small populations [ 80 ]. Recent evidence from white-throated sparrow ( Zonotrichia albicolis ) song has highlighted a similar pattern of west to east song transmission across Canada, but with a far slower spread (a few decades versus two years) [ 81 ].…”

“…Finally, there is clear evidence that innovation and social learning are repeated over time and in multiple populations to generate changes to the song [ 20 , 52 , 57 , 80 ]. Song changes in a unidirectional manner over multiple years in a population at all levels in the song hierarchy [ 52 , 53 , 85 ]; males must repeatedly learn these changes and incorporate them into their own song to maintain the observed conformity.…”

Vocal learning in animals and humans

“…They find that the phylogenetic signal can be as great, or even greater, for learnt songs as for unlearnt ones. Zandberg et al [37] present cultural evolutionary simulations of humpback whale song transmission based on empirical data collected over 10 years in the Southern Hemisphere population. Using observed values for interactions between animals in the Southern and Northern Hemispheres, they simulated the observed patterns of song evolution in both hemispheres.…”