(April 28th, 2016) Killer whales use sound to navigate and communicate. They converse in vocal dialects, a unique repertoire of calls shared by each pod of whales. By using an agent-based computer model of call evolution, Scottish scientists analysed which factors influence the whales' language.
Killer whales (Orcinus orca) have a strong bond with their mothers. Up to four generations of sons and daughters remain with the matriarch. When she dies, the surviving daughters form new units. When pods separate, their call repertoires diverge. Calves learn the call repertoire from their matrilineal family. Members of different pods recognise and track each other over long distances via their distinct calls. This is particularly important when different pods mix and produce a cacophony of sounds. By comparing recent and historical call repertoires, scientists have discovered that the repertoires have remained stable over nearly five decades.
As long ago as 1991, the Canadian marine ecologist John Ford proposed in the Canadian Journal of Zoology that killer whale calls changed mostly through random error and occasionally through innovation. To test this hypothesis, whale expert Olga Filatova created an artificial population of ‘agents’ or ‘virtual‘ whales using published data on demography and social structure. To determine which mechanisms of cultural transmission may govern the formation of killer whale dialects, she used this model to apply different sets of vocal-learning rules.
“I found that random errors are not sufficient, and even in combination with innovations do not produce the picture we see in the wild, so some other processes appear to be involved”, Filatova, now a Senior Research Fellow at Moscow State University, explained. The model suggests that group-specific call repertoires might be generated, for example, by learning from the mother or the matrilineal unit, the tendency to diverge from kin by random error and by the influence of innovation.
“Ford also assumed that the calls diverge proportionally to the social divergence. This would mean that recently diverged matrilines, which spend more time together, have more similar calls than matrilines that diverged long ago. I found that this is not always the case”, she added. The results were published last year in the Journal of Theoretical Biology. In a recent review article in the journal Behaviour, Filatova and her colleagues suggested that several other factors might influence the evolution of whale dialects. Temporal changes which occur at different speeds in different syllables and structural categories of killer whale calls, or learning from members of the same generation across different matrilineal units might modify call evolution. Furthermore, the variability of call structure might be limited due to physical constraints of the vocal apparatus.
Filatova developed these models together with her colleagues while she was a Research Fellow in Patrick Miller’s lab at the Scottish Oceans Institute at the University of St Andrews. She was funded for two years by a Marie Curie International Incoming Fellowship. With these individual fellowships financed under the Seventh Framework Programme, the European Commission wanted to attract top-class researchers from third countries to work and to undertake research training in Europe. ”My first proposal, which took me a month to write, was not successful. The following year, I spent a further month improving my application and finally obtained the fellowship”, the whale specialist recalled.
Asked, how the idea for the project came up, she explained: “I’ve been studying killer whale dialects in the Russian Pacific since 2000. At first, I assumed from Ford's work that when I described the dialects, I would be able to build a consistent genealogy using the similarity of dialects. When I found out that this was not the case, I wanted to improve the model of whale dialect evolution.” She said that the University of St Andrews was an ideal place for her project because it had two of the best research groups studying animal culture and cognition and marine mammals. “I enjoyed working in this multi-disciplinary setting and communicating with all these different scientists from different fields”, Filatova added.
Since 2011, the marine ecologist has published five studies on killer whales. Last year, she was awarded a three-year Pew Fellowship of over £97,000 to investigate the diversity and habitats of cetaceans in Russian waters. She will analyse their distribution, numbers and population structure in this area using surveys, photographic and acoustic identification, behavioural observations, and genetic analyses. The results of her studies could lead to the establishment of protected areas for cetaceans which are increasingly threatened by industrial activity, severe overfishing, hunting and the capture of live creatures.
As a genuine whale enthusiast, the marine ecologist is chair of the orca working group of the Russian Marine Mammal Council and led the development of a scientific research plan for the Russian Cetacean Habitat Project funded by the Whale and Dolphin Conservation Critical Habitat Program. This summer, she will leave her comfortable lab for some time to make new recordings in the Russian Far East. Her current research focuses on the interplay between social structure and dialect change. This video of the Far East Russia Orca Project, of which Olga Filatova is, of course, a member, gives exciting insights into the work in the field.
Photo: Olga Filatova/FEROP