The role of individual behaviour in the collective cultural evolution of humpback whale songs

For more than forty years, the complex songs emitted by humpback whales have fascinated the scientific community as well as the general public. These songs are produced by males during the breeding season, and are hierarchically structured and population specific. Within a population, males tend to conform to the same song type, but songs undergo gradual unidirectional change. Instances of more rapid song changes have also been recorded, where the song sung by a population has been replaced by the song of an adjacent population. The learning mechanisms that concurrently drive song conformity, and simultaneously allow gradual (evolution) and rapid (revolution) song change are not currently understood. This thesis aims to address this gap by using innovative theoretical models as well as more established empirical methods. Chapter 1 provides a general introduction to the thesis topics. In chapter 2 I introduce a spatially explicit agent-based modelling approach to investigate humpback whale song evolution and transmission. I found that shared feeding grounds promote inter-population song transmission, song conformity emerges as a function of breeding ground geographical segregation, and production errors facilitate gradual evolution of songs. In chapter 3, the same modelling approach is extended to simulate song revolutions using a new learning bias in combination with different movement scenarios. I found that the consistent emergence of song revolutions is dependent on cognitive (song memory), behavioural (singing probability) and spatial (agent density) factors. Finally, in chapter 4, I analyse intra- and inter- individual song variability at different hierarchical levels of organisation in songs recorded off eastern Australia. I found that variability is not homogeneously distributed across the different song levels. Furthermore, I identified consistent and distinctive individual patterns of song production consistent with the theory that songs could represent mate quality advertisements for females."This work was supported by Leverhulme Trust Grant [grant number: RPG-2013-367]" -- Acknowledgement

Global cultural evolutionary model of humpback whale song

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 PDFPeer reviewe

Global cultural evolutionary model of humpback whale song

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

Variability in humpback whale songs reveals how individuals can be distinctive when sharing a complex vocal display

Funding: L.L. was supported by a Leverhulme Trust Grant to L.R. (among other recipients; grant reference RPG-2013-367). L.R. was supported by the MASTS pooling initiative (The Marine Alliance for Science and Technology for Scotland) and their support is gratefully acknowledged. MASTS is funded by the Scottish Funding Council (grant reference HR09011) and contributing institutions. ECG was funded by a Royal Society Newton International Fellowship and a Royal Society University Research Fellowship. J.A.A. was funded by an Australian Government Research Training Programme Scholarship and the Australian American Association University of Queensland Fellowship. The HARC project was funded by the US Office of Naval Research, the Australian Defence Science and Technology Organisation, and the Australian Marine Mammal Centre.Individually distinctive acoustic signals in animal vocal communication are taxonomically widespread, however, the investigation of these signal types in marine mammals has focused only on a few species. Humpback whale songs are a stereotyped, hierarchically structured vocal display performed by males, and hence thought to be sexually selected. Within a population, whales conform to a common version of the song despite the song constantly evolving. While humpback songs have been studied extensively at the population level, individual level variation has been rarely described, with inconclusive results. Here we quantified inter- and intra-individual variability at different levels in the song hierarchy using songs from 25 singers across two song types from the eastern Australian population song of 2002 (12 singers), and the revolutionary song introduced in 2003 (13 singers). Inter- individual variability was found heterogeneously across all hierarchical levels of the song structure. In addition, distinct and individually specific patterns of song production were consistently recorded across song levels, with clear structural differences between the two song types. These results suggest that within the constraints of song conformity, males can produce individually distinctive patterns that could function as an advertisement to females to convey individual qualities.Publisher PDFPeer reviewe

Adapting a computational multi agent model for humpback whale song research for use as a tool for algorithmic composition

Humpback whales (Megaptera Novaengliae) present one of the most complex displays of cultural transmission amongst non-humans. During breeding seasons, male humpback whales create long, hierarchical songs, which are shared amongst a population. Every male in the population conforms to the same song in a population. During the breeding season these songs slowly change and the song at the end of the breeding season is significantly different from the song heard at the start of the breeding season. The song of a population can also be replaced, if a new song from a different population is introduced.This is known as song revolution. Our research focuses on building computational multi agent models, which seek to recreate these phenomena observed in the wild.Our research relies on methods inspired by computational multi agent models for the evolution of music. This interdisciplinary approach has allowed us to adapt our model so that it may be used not only as a scientific tool, but also a creative tool for algorithmic composition. This paper discusses the model in detail, and then demonstrates how it may be adapted for use as an algorithmic composition tool