The research team studying vocal dialects in the endangered population of sperm whales that live in the Mediterranean Sea have captured the cultural evolution of new dialects in process. Using 20 years of recordings they showed that whales living in the eastern Mediterranean around the Hellenic Trench in Greece had developed a new form of the vocal dialect used by animals in the western basin, studied around the Balearic Islands. The paper is published in Proceedings of the Royal Society B today [24 June].
While it might surprise some to learn that sperm whales, the largest of the toothed whales, can be found swimming in the holiday-destination waters off Mallorca and Crete, it's thought that they first entered the Mediterranean around 20,000 years ago and since then have made their way from Gibraltar to become established throughout the Mediterranean. The population is genetically isolated from other oceans and small, around a few thousand animals, so it is considered endangered because of its small size and serious threats from fishery entanglement and ship strikes.
Sperm whales make a social vocalisation called codas that are short, stereotyped patterns of clicks, and use them to identify themselves as belonging to larger cultural groups called vocal clans. Previously it was thought all the whales in the Mediterranean belonged to the same clan, identified by a single predominant coda type consisting of three clicks and then a pause before the fourth and final one – a pattern called the '3+1' type.
However, the new results, showed that whales recorded around the Hellenic Trench, a deep-water feature centred off Crete, produced a distinct, faster form of this '3+1' type compared to animals in the western basic between Gibraltar and Italy. Crucially though on some days some of these groups decided to go retro and produced the slower western form of the coda as well, showing they were familiar with both dialects.
Dr Luke Rendell, Reader at the University of St Andrews Sea Mammal Research Unit who coordinated the collaborative study, said: "The Mediterranean has been the cradle of significant aspects of human cultural evolution from ancient Greece onwards. Over that entire period, sperm whale culture has also been evolving – we now have a much better idea of just how slow that process is. It also helps us understand the origins of dialect diversity in sperm whales globally. But there are still many unanswered question, like why did that new dialect evolve at all and in that particular location."
Lead author Dr Taylor Hersh, HFSP Research Fellow, who carried out the study while at St Andrews, and is now in the School of Biological Sciences at the University of Bristol, added: "These findings paint a picture of the history of sperm whales living in the Mediterranean, consistent with a progressive occupation from west to east, ending with the development of a distinctive dialect in the animals living in the east, starting in the Hellenic Trench. What's interesting is that the new dialect is clearly modified version of the presumably ancestral slow 3+1 and that groups in the east also clearly remember that dialect as they have these 'throwback' days."
Dr Alexandros Frantzis, the lead of Pelagos Cetacean Research Institute, the Greek team involved in the study, said: "It's one of the most interesting publications in which we have participated. Apart from sperm whale conservation, decoding mysteries of sperm whale communication was one of the main motivations for our studies on sperm whales in the Eastern Mediterranean, since we discovered their population three decades ago."
Dr Txema Brotons, of Asociación Tursiops the Spanish team involved in the study, added: "This finding reminds us that the cultural history of the Mediterranean does not belong exclusively to humans. While the civilizations of the Mare Nostrum were developing their own languages, customs and identities, sperm whales were also passing down their vocal traditions from one generation to the next. The Mediterranean is therefore a space of shared cultural diversity, where the evolution of human culture and animal culture has coexisted for thousands of years."
The researchers emphasised that long-term international collaboration has been crucial to this new understanding, and that studying these dialects provides important new information about the population structure and social dynamics of this endangered population, at a time when our understanding of the importance of considering cultural factors in the conservation of large animals, at a time when our understanding of the importance of considering cultural factors in the conservation of large animals continues to grow.
Paper
'Dialect variation in Mediterranean sperm whales shows evidence of cultural evolution in an isolated population' by Taylor A. Hersh, Luke Rendell et al. in Proceedings of the Royal Society B [open access]
