Researchers have discovered that sperm whales in the eastern and western Mediterranean basins use distinct vocal dialects, shedding light on how these communication patterns evolve in isolated populations.
Two dialects identified
Scientists analyzed hydrophone recordings of sperm whale groups made over 112 days between 2003 and 2021. The recordings were taken near the Hellenic Trench off Greece (eastern basin) and around the Balearic Islands off Spain (western basin). They found that most codas—sequences of short clicks used for communication—involved four clicks in both areas. However, the rhythmic pattern differed: whales in the west favored a "3+1" coda with three regularly spaced clicks, a longer pause, and then another click, while those in the east used a faster version of the same pattern.
"The dialect is used to form social structures, within which these animals will cooperate," said Dr. Luke Rendell of the University of St Andrews, a co-author of the study. He drew parallels to how humans might feel more comfortable conversing with someone who sounds similar.
Cultural evolution in isolation
The findings, published in Proceedings of the Royal Society B, suggest that sperm whales first colonized the western Mediterranean and then spread eastward, where their dialect gradually changed. "The whales in the east remember the old ways, but they're moving on and they've got a slightly different version of what is clearly the same [general type of coda], but they've evolved it a little bit; they've changed it," Rendell said.
Genetic studies have previously indicated that Mediterranean sperm whales are isolated from other populations, and mating between eastern and western groups is restricted, though some individuals move between basins. The new research shows that dialect formation is a slow process requiring population isolation, similar to cultural evolution in human languages and birdsong.
"This is the first example we've got where we can look at a snapshot and think: 'Oh, this seems to be telling us about how new dialects come about'," Rendell noted. "We just knew there were these different dialects, but we've never seen the origin or had any clues into the origin of them."
Implications for conservation
The Mediterranean sperm whale population is small and endangered, numbering only a few thousand individuals. Understanding their social structure and communication may aid conservation efforts, as these whales rely on vocal clans for cooperation and social bonding. The study highlights the importance of preserving the distinct cultural groups within this population.
