Cultural transmission of tool use in bottlenose dolphins

Abstract

In Shark Bay, wild bottlenose dolphins (Tursiops sp.) apparently use marine sponges as foraging tools. We demonstrate that genetic and ecological explanations for this behavior are inadequate; thus, ''sponging'' classifies as the first case of an existing material culture in a marine mammal species. Using mitochondrial DNA analyses, we show that sponging shows an almost exclusive vertical social transmission within a single matriline from mother to female offspring. Moreover, significant genetic relatedness among all adult spongers at the nuclear level indicates very recent coancestry, suggesting that all spongers are descendents of one recent ''Sponging Eve.'' Unlike in apes, tool use in this population is almost exclusively limited to a single matriline that is part of a large albeit open social network of frequently interacting individuals, adding a new dimension to charting cultural phenomena among animals.culture ͉ Tursiops sp. ͉ social learning ͉ tradition

Social networks reveal cultural behaviour in tool-using dolphins

“…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 transmission 10,11,14 , consistent with mitochondrial DNA analysis 13,15 .…”

“…Many, but not all, animals that use these channels specialize in sponging and spongers spend more time using tools than any non-human animal 10 . So, although Krützen et al 15 did not demonstrate social learning per se, the social contribution is well-documented elsewhere 10,11,14 and the strong ecological component does not refute the argument that sponging is socially learned.…”

“…Non-social variables included sex, foraging type, kinship and location. We documented matrilineal relatedness for 28 of 36 spongers (known mother and/or offspring, including some offspring that did not adopt sponging) and for 98 of non-spongers; genetic relatedness was known for only 14 of these spongers 13,15 . As we have documented matrilineal relationships for 27 years, these data represent kinship that dolphins themselves would recognize through association with the mother, although additional kin recognition mechanisms are possible 30 .…”

“…The initial 'culture' claim for sponging proved contentious [16][17][18] , largely stemming from application of the exclusion method 15 to demonstrate social learning, and hence cultural behaviour. This method involves trying to eliminate genetic and environmental explanations for a behavioural variant in a wild population, thus leaving social learning as the most plausible explanation for the variant 19 .…”

The effect of innovation and sex-specific migration on neutral cultural differentiation

“…Langergraber et al 2011) with studies of covariance in kinship and behavioural variants (e.g. Krützen et al 2005) could provide a more powerful method to differentiate between an innate genetic basis and social learning.…”