Cultural transmission of humpback whale song and metapopulation structure in the western and central South Pacific Ocean

• Main Author: Ellen Clare Garland
• Format: Thesis
• Language: unknown
• Published: The University of Queensland, School of Veterinary Science 2011
• Subjects: song; cultural transmission; population structure; acoustic display; non-human culture; humpback whale; Megaptera novaeangliae; South Pacific Ocean; 07 Agricultural and Veterinary Sciences; Pacific; Tonga; Humpback Whale
• Online Access: https://espace.library.uq.edu.au/view/UQ:259485/s41119491_phd_finalthesis.pdf; https://espace.library.uq.edu.au/view/UQ:259485

Male humpback whales produce a long, complex and highly stereotyped acoustic display termed ‘song’. The exact function of song is unclear but it is believed to be involved in sexual selection through mate attraction and/or male social ordering. All males within a population adhere to the current content and arrangement of the display. Song is highly plastic as it progressively evolves over time and all males are required to make similar changes to maintain the observed conformity. Within an ocean basin, populations sing similar songs with the level of similarity based on the geographical distance between populations. This conclusion is based predominately on studies conducted in the North Pacific which have usually been drawn from a single synoptic year of data. Currently, no studies have investigated the long-term dynamics of ocean basin song. Therefore, the primary aim of this thesis was to investigate the dynamics and thus pattern of cultural transmission of humpback whale song within an ocean basin. Secondarily, I aimed to use this information to produce an acoustically-derived understanding of population structure. This was achieved by analysing extensive song data from multiple populations located within the western and central South Pacific region over eleven consecutive years. To investigate song similarity, data were first required to be transcribed by hand to produce a large qualitative description of all songs (termed song types) present within the region over the eleven year time period. Each of the 67 themes identified were assigned to one of the 11 song types which were given arbitrary colour names. This is the largest description to date of different versions of this display and represents a significant foundation for this thesis. Song types were observed to move in an easterly direction from the western-most population of eastern Australia across the region to French Polynesia. The movement of song types frequently caused complete ‘cultural revolution’ to the display. This unidirectional propagation produced multiple ‘cultural waves’ which were regular and repeated, taking approximately two years to transit the region. The only previous documentation of rapid population-wide cultural change occurred in the song of the eastern Australian humpback whales when a new, novel song type was introduced from the western Australian population and rapidly revolutionised the existing song type. This original ‘cultural revolution’ can now be traced moving across the South Pacific region in this thesis and represents the survival of a highly plastic cultural signal (song type) spanning seven years and two ocean basins. To further investigate ocean basin song similarity at both the population and individual level, quantitative analyses were undertaken. The Levenshtein distance method was used to understand the relationship among population or individual displays based on the calculated similarity of call sequences. Humpback whale song is produced in a stereotyped sequence which allowed the quantification of different versions of the display through clustering of similar sequences to assign song types. Clustering did not occur based on geographic location or the year the song was recorded. Thus, it represented an index of similarity based on the cultural signal which allowed the changes to that signal to be quantitatively traced. An acoustically-derived population structure was developed from this quantitative analysis based on yearly similarity due to the dynamic nature of the display. This resulted in three distinct but interconnected population groupings for the region. The western group contained a single population, eastern Australia, the central group was comprised of New Caledonia, Tonga and American Samoa and finally an eastern group contained the Cook Islands and French Polynesia. This broadly agrees with concurrent genetic and photo-identification studies within the region, and suggests the combination of all three platforms will help elucidate the region’s complex metapopulation structure. This thesis describes the rapid, regular and repeated horizontal cultural transmission of multiple song types of a highly plastic display across a vast oceanic region. This is the first study to investigate the previously unknown dynamics of song movement and to use these results to produce, using quantitative techniques, a population structure based on acoustic display similarity. Future work is required to understand the applicability of these large-scale song dynamics to other ocean basins, the fine-scale aspects of song evolution and revolution, and to further investigate the role and conforming influence of culture on this sexually selected display.