Social networks and culture among dolphins
Recently published research in Nature Communications ‘Social networks reveal cultural behaviour in tool-using using dolphins‘ is exploring social networks of dolphins. In particular, it finds evidence for homophily on a learned skill which leads that there’s an exclusion and cultural contagion even among cetaceans.
Animal tool use is of inherent interest given its relationship to intelligence, innovation and cultural behaviour. Here we investigate whether Shark Bay bottlenose dolphins that use marine sponges as hunting tools (spongers) are culturally distinct from other dolphins in the population based on the criteria that sponging is both socially learned and distinguishes between groups. We use social network analysis to determine social preferences among 36 spongers and 69 non-spongers sampled over a 22-year period while controlling for location, sex and matrilineal relatedness. Homophily (the tendency to associate with similar others) based on tool-using status was evident in every analysis, although maternal kinship, sex and location also contributed to social preference. Female spongers were more cliquish and preferentially associated with other spongers over non-spongers. Like humans who preferentially associate with others who share their subculture, tool-using dolphins prefer others like themselves, strongly suggesting that sponge tool-use is a cultural behaviour.
In Shark Bay, Australia, a subset of the community of Indo-Pacific bottlenose dolphins (Tursiops sp.) procure and wear basket sponges on their beaks while lightly scouring the seafloor for prey in deep (8–13 m) channels (Fig. 1)9, 10, 11, 12. Sponging is the best-documented case of tool use by wild cetaceans and is unique among wildlife in that only a small subset of the population uses tools. This exceptional case of tool-use heterogeneity allows us to test for preferential affiliation based on tool-use. To date, 55 dolphins have been documented habitually using sponges in the eastern gulf of Shark Bay12, although sponging also occurs in the western gulf13. Only calves of spongers become spongers (24 offspring to date), but 8 offspring of spongers never adopted sponging. Sponging is a solitary activity, but calves accompany their mothers during sponging and vertical social learning is strongly implicated as the primary mechanism of transmission10, 11, 14, consistent with mitochondrial DNA analysis13, 15
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