Report: Integrating Genetic, Environmental, and Social Networks to Reveal Transmission Pathways of a Dolphin Foraging Innovation
by Sonja Wild et al.
Current Biology, Vol. 30, Issue 15
Published: 25 June 2020
Excerpt: pp. 3026-3027
Multi-network NBDA revealed most support for a transmission pathway of the foraging technique shelling among associated dolphins, providing the first quantitative evidence of a non-vertically transmitted foraging behavior in a toothed whale species while also statistically controlling for genetic and environmental influences. Our results do not distinguish between horizontal and oblique transmission, but include all non-vertical social transmission outside of the mother-calf bond. These results are surprising, insofar as vertical social transmission between mother and offspring has been established as the primary mechanism for learning foraging behaviors in Shark Bay’s dolphins, e.g., [6, 9, 15], and, in fact, toothed whales in general, e.g., [25–29]. Close proximity between mother and offspring during dependency combined with prolonged parental care provides ample opportunities for social transmission of behavior, explaining the prevalence of vertical transmission [9, 30]. Our results quantify non-vertical transmission of shelling, however, illustrating that free-ranging dolphins are also capable of learning foraging behavior outside the mother-calf bond. This builds upon previous cases of presumed horizontal transmission of behavior in toothed whales that were descriptive or anecdotal in nature [31–33]. Social learning opportunities increase with the duration and frequency of proximity between demonstrator and observer [34]. Both females and, in particular, allied male dolphins in Shark Bay show high levels of social tolerance within cohesive social groups [35–37], which manifests itself in spatial proximity during foraging and, we hypothesize, may have facilitated the horizontal spread of shelling.
Our results further illustrate that dolphins were not only capable but also motivated to learn from others. Prior research on this population suggested that dolphin calves primarily followed their mothers in adopting the techniques requiring high levels of specialization: the use of sponges as foraging tools (‘‘sponging’’), for example [38, 39], which is transmitted vertically from mother to primarily female offspring [6, 40, 41]. Offspring tend to incorporate their mothers’ home range into their own [42], which warrants selection for the same foraging specializations [9]. As such, and in order to avoid acquiring unsuitable or even maladaptive behavior, calves tend to follow a do-as-mother-does strategy for specialized techniques [9]. Shelling, however, occurs on an opportunistic basis, with all shellers also engaging in other strategies, and does not appear to require the same level of specialization. This reduces the potential costs associated with learning a new foraging behavior and may thereby facilitate the horizontal or oblique spread of shelling.
NBDA
«Network-Based Diffusion Analysis» to detect social transmission, p.3024 (left column)
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