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Cetacean Use of Representational Acoustic Signals

Periodic Reporting for period 1 - CURAS (Cetacean Use of Representational Acoustic Signals)

Reporting period: 2015-08-25 to 2017-08-24

This project involved two studies.
Study 1:
Dolphins use sound to identify each other through signature whistles, alleviating problems identifying individuals in opaque environments. Dolphins' use of signature whistles is different from many other mammals, which identify individuals using odour cues from bodily fluids. Social recognition by smell is possible in many mammals because individualized gene complexes are transcribed into odor molecules creating a ‘smell fingerprint’. It was previously assumed that chemical communication plays a diminished role with dolphins because they lack olfactory (smell) genes or an olfactory bulb. Yet wild dolphins often engage in oral sampling of their social partner’s excreta. Could the loss of smell have led to an increase in taste perception for dolphins? If so, what kind of social information is present in dolphin urine? How do taste signals work in communication despite the absence of smell perception?
Study 2:
We examined representational signal use in dolphins. Names for individuals are a universal feature of human language as referential labels that not only identify everything the person hearing the social signal associates with the name-bearer, but identify all aspects tied to identity including appearance, voice, style of dress, smell, shared history, reputation, etc. Naming is an important aspect of sociality, human language & cognition allowing individuals to think abstractly making our representations more efficient by tying physical & mental traits behind a name. The ability to refer to other individuals without their presence offers evidence of complex cognition & could open up the possibility of studying abstraction in non-human animals. Studying potential ‘names’ in non-human animals can also give new perspective in areas related to the potential of language-like communication outside our species. Therefore, the specific aim of this study was to determine if identity can be recognized independent of the type of sensory system used, suggesting representation of an individual in the dolphin’s mind across two communication channels.
This important research can further understanding not only of dolphin communication & cognition but also of evolution of cognition & language in general, including that of humans. Secondly, it can help explain the evolution of taste & smell in mammals. Thirdly, the results might have implications for human taste perception which is still poorly understood & tied directly to obesity. Finally, the results could impact European policy on marine noise or release of chemicals that could mask dolphin taste perception.
Objectives
1) provide evidence for dolphin chemosensory (taste) recognition
2) use chemical & acoustic playbacks to study representational signaling in dolphins.
CURAS achieved these objectives & increased the knowledge base on dolphin communication & cognition.
Study 1:
Dolphins were presented with urine samples from familiar & unfamiliar dolphins, or water. CURAS found the first evidence that chemical communication in dolphins retains the mammalian typical role of social identity signaling, despite dolphins' anatomical & physiological differences from land mammals. This marks the first vertebrate species known to chemically signal social information by gustation alone, demonstrating a previously unseen mechanism of social signalling.
Our findings indicate that dolphins can recognize the urine of familiar dolphins through gustatory means alone. Results suggest an underestimation of the role gustation plays in animal communication, with specific implications for our own perception of fat molecules.
Study 2:
Cross-modal playbacks were used to identify whether dolphins have a modality independent understanding of signature whistles (>100 presentations to dolphin subjects). Results showed that dolphins are capable of modality-independent representational understanding of one another. Results also show that social labeling found in dolphin communication has a meaningful communicative analogue with human language. Given the innovated nature of the signal & the scarcity of evidence for this type of social labeling broadly, signature whistles are probably the best-supported analogue to an aspect of human language yet found in a non-human mammal. Along with studies showing whistle copying as a means of social addressing, this study fundamentally addresses the skeptical interpretations of signature whistles as non-referential & shows that the use of signature whistles by both dolphins & human experimenters is serving to elicit social identity information relative to the subject of the whistles. This has implications for the perceived function of whistle matching & addressing, drawing parallels to human use of names, as well as signature whistle memory as a proxy for conspecific memory. Dolphin signature whistles have now met the criteria to be considered representational.
Project results were presented in numerous outreach events. Dr Bruck gave talks to three primary schools (two in Scotland & one via teleconference to Cote d’Ivoire) & presented interactive research displays at six outreach events, where European youth were able to perform dolphin playbacks. He also gave a public talk on the research conducted under this fellowship at Dolphin Quest (>70 attendees). A website was created providing information on dolphin communication & cognition, educational resources for primary school teachers to use in their classrooms, & a series of short web episodes giving an overview of marine mammal cognition & communication.
Project data will be made available via dryad or St Andrews University data repository upon publication of papers.
The project represents the most advanced & cutting-edge techniques in the study of animal minds. Cross-modal playbacks are a technical innovation in cetacean work & the use of chemical playbacks in a dolphin had not previously been attempted despite the potential of gustation as a communication channel for dolphins. More broadly, no research before CURAS has shown true natural representational signalling in a learned & innovated non-human signal. This is important as it offers the closest known parallel to human language yet found in a non-human mammal, as we now know dolphins have a social naming system comparable in many ways to our names. Since non-human primates cannot invent or copy new sounds, results from nonhuman primates do not show the use of learned sounds in this way which explains the novelty of these results. At present, this represents the best study paradigm for understanding the nature of representation in animal cognition as it may pertain to language in non-human species, especially given the mammalian lineage of dolphins.
CURAS impacts:
•Redefined “language-like” representation in signature whistles, with implications for evolution of human language system
•Increase European competitiveness in terms of expertise in animal communication & language-like capacity as well as comparative cognition
•Increase community awareness of science, dolphins, conservation & animal communication
•Enable primary school teachers to increase children's scientific literacy through student-led videos & guides
•Increase scientific knowledge of noise & chemical pollutant effects on wild dolphins
•Open the door for research investigating the potential for lipid reception taste sensation/perception & its role in obesity
Training dolphins to give urine samples
Recording dolphin responses during tests
Presenting the results of CURAS to school children