Using agent-based models to understand the role of individuals in the song evolution of humpback whales (Megaptera novaeangliae)

Abstract

Male humpback whales produce hierarchically structured songs, primarily during the breeding season. These songs gradually change over the course of the breeding season, and are generally population specific. However, instances have been recorded of more rapid song changes where the song of a population can be replaced by the song of an adjacent population. The mechanisms that drive these changes are not currently understood, and difficulties in tracking individual whales over long migratory routes mean field studies to understand these mechanisms are not feasible. In order to help understand the mechanisms that drive these song changes, we present here a spatially explicit agent-based model inspired by methods used in computer music research. We model the migratory patterns of humpback whales, a simple song learning and production method coupled with sound transmission loss, and how often singing occurs during these migratory cycles. This model is then extended to include learning biases that may be responsible for driving changes in the song, such as a bias towards novel song, production errors, and the coupling of novel song bias and production errors. While none of the methods showed population song replacement, our model shows that shared feeding grounds where conspecifics are able to mix provide key opportunities for cultural transmission, and that production errors facilitated gradually changing songs. Our results point towards other learning biases being necessary in order for population song replacement to occur.

Cultural Transmission, Evolution, and Revolution in Vocal Displays: Insights From Bird and Whale Song

“…The new song variants in corn buntings show relatively limited change, making it more likely that change resulted from a learning or production error at the beginning of the season ( McGregor et al, 1997 ). A similar process may occur in humpback song; recent work using agent-based models of song evolution demonstrated that production errors ( rate = 1 or 0.1%) facilitated the gradual song evolution observed in the wild ( Mcloughlin et al, 2018 ). Using both novelty bias and production errors in the model mirrored the progressive song evolution observed in the South Pacific ( Mcloughlin et al, 2018 ).…”

“…A similar process may occur in humpback song; recent work using agent-based models of song evolution demonstrated that production errors ( rate = 1 or 0.1%) facilitated the gradual song evolution observed in the wild ( Mcloughlin et al, 2018 ). Using both novelty bias and production errors in the model mirrored the progressive song evolution observed in the South Pacific ( Mcloughlin et al, 2018 ). However, no scenarios resulted in song revolutions; to produce a revolution in the agent-based model required a song memory to be added ( Lamoni, 2018 ).…”

“…Controlled-environment studies of factors influencing whale song cultural transmission in both field and lab experiments are unlikely in the foreseeable future because of insurmountable practicalities; for example, humpback whales are 14 m long, weigh 30 tonnes, and migrate ~6,000 km one-way. While agent-based models can provide an informative framework for investigating various social learning scenarios ( Mcloughlin et al, 2018 ), all types of model can lack real-world applicability. Therefore, a comparative approach is currently the best option to understand the key factors of such phenomena.…”

Song Morphing by Humpback Whales: Cultural or Epiphenomenal?

“…The ways in which they progressively morph phrases within and across songs does not match with what selectionist models of cultural evolution predict should happen, but neither do they match with a neutral model of evolutionary change in which random mutations spread through a population ( Kimura, 1979 ). Evolutionary models of collective changes appear to be inadequate for characterizing the ways in which singers modify their songs over time ( McLoughlin et al, 2018 ). Whether dynamic systems models of interacting agents can meet this challenge remains to be seen.…”

Acoustic communication of female-calf humpback whales during migration

“…Although it is presumed that song transmission is facilitated by male interchange between populations on shared feeding grounds (Garland et al 2013;McLoughlin et al 2018) or via transfer along shared migratory routes (Noad et al 2000;Garland et al 2011), the specific function of song change, the significance underlying rapid versus progressive changes, and the contribution of individual inventiveness as opposed to "template" patterning has yet to be determined.…”