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’.

Highlights

  • Social learning underpins a wide variety of behaviours in many species of animal

  • With simple song learning rules, we have been able to replicate the patterns of the cultural evolution of humpback whale song as found in the Southern Hemisphere

  • Similar to the empirical data, the majority of our simulations resulted in revolutions running in an eastward direction, which was related to the size differences among populations

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Summary

Introduction

Social learning underpins a wide variety of behaviours in many species of animal. Social learning (from the observation of, or interaction with, others) can lead to innovations spreading through a population (e.g. [1,2,3,4]) or could, on longer timescales, potentially lead to the emergence of local cultures (e.g. [5,6,7,8,9]). What processes (e.g. production errors, innovations), learning biases or individual(s) may be driving this evolutionary change, and how this may relate to fitness, female choice and reproductive success, remains elusive [25] Another key feature of humpback whale song is at the scale of oceans: within oceans, populations sing similar songs but the degree of similarity depends on the geographical distance and appears to depend on the extent of interchange among populations [31,32,33]. The Northern Hemisphere populations are constrained by continents on each side of the oceans, which prevents interaction between Atlantic and Pacific meta-populations, while at the same time encourages multiple populations to interact within an ocean by funnelling populations into comparatively small areas (figure 1a) [25] Testing such hypotheses is unfeasible; humpback whales cannot be kept in captivity, as they are 14 m long, weigh 30 tonnes and undertake long migrations across half the globe. By using models to explore likely scenarios, targeted future field studies can be designed to empirically test hypotheses

Methods
Results
Discussion
40. Baker CS et al 1986 Migratory movement and
52. Garland EC et al 2015 Population structure of
56. Jackson JA et al 2015 Southern Hemisphere

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