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Topic: Vocal learning and communication in dolphins

Final draft

Dolphin communication has been of great interest to scientists partly because of the wide array of techniques that they exhibit. Bottlenose dolphins communicate through burst pulsed sounds, whistles, and body language. Examples of body language include leaping out of the water, snapping jaws, slapping the tail on the surface and butting heads. The whistle sounds, which are the more lyrical tones, allow dolphins to stay in contact with each other (especially, mothers and offspring), and to coordinate hunting strategies. Sounds and gestures help keep track of other dolphins in the group, and alert other dolphins to danger and nearby food. They produce sounds using six air sacs near their blow hole since they lack vocal cords. A particularly interesting technique that dolphin exhibit is vocal learning. Vocal learning is the ability to modify acoustic sounds, acquire new sounds through imitation or mimicry, and produce vocalizations. Vocal learning is a relatively rare trait despite the wide array of vocalizing species. It has only been detected in eight animal groups so far which include; humans, bats, cetaceans, pinnipeds (seals and sea lions), elephants, and three distantly related bird groups including songbirds, parrots, and hummingbirds. We will examine the development of vocal learning in bottlenose dolphins (Tursiops truncatus) which are a part of the cetacean group. Jarvis (2009) examined several proposed hypotheses that explain the selection for vocal learning based on environment and behavior. Most of the experimental data collected to support these hypotheses involve birds, which are the most notable vocal learners in the animal kingdom. But these hypotheses can be contributed to the knowledge of dolphin communication as well. One hypothesis proposes evolution due to individual identification. In most vocal-learning species, individuals have their own calls, signals and songs which serve as a unique signature to differentiate themselves from others in the population, which some suggest has driven selection of vocal learning. For example, Caldwell et al. (1990) describes a ‘signature whistle’ as a dominant whistle produced by dolphins, which is uniquely characteristic to that particular individual. They hypothesized that the distinctive attributes of signature whistles function to transmit the identity and location of the whistler to other dolphins. This individual distinctiveness could drive evolution by providing higher species fitness since complex communication is largely correlated with increased intelligence. However, vocal identification is present in vocal non-learners as well. Therefore, it is unlikely that individual identification was a primary driving force for the evolution of vocal learning. Semantic communication is another proposed cause of the evolution of vocal learning. Semantic vocal communication associates specific vocalizations with different meanings. This hypothesis asserts that vocal learning evolved to assist in the improved communication of these specific meanings as opposed to affective communication, which conveys emotional content. However, Caldwell (1977) observed that because bottlenose dolphins perceive and discriminate a wide range of sounds, there is strong probability that they use sound in the communication of a variety of emotions in addition to relaying such information as the presence of food or danger. Similarly it has been observed in other studies that dolphins are capable of discerning meaning in sign language and in human gestures. Likewise, many vocal non-learners, including chickens and vervet monkeys, have been shown to use their innate calls to communicate semantic information such as a food source or presence of a predator (Podos. 2002). Further discrediting this hypothesis is the fact that vocal learning in birds also use innate calls for this purpose and only rarely use their learned vocalizations for semantic communication. Therefore as learned vocalizations rarely convey semantic information, this hypothesis also does not fully explain the evolution of vocal learning. Mate attraction and territory defense have also been seen as possible contributors to vocal learning evolution. This hypothesis points out that while both vocal learners and non-learners use vocalizations to attract mates or defend territories, there is one key difference: variability. Vocal learners can produce a more varied arrangement of vocalizations and frequencies, which studies show may be more preferred by females. For example, Caldwell (1977) observed that male Atlantic bottlenose dolphins may initiate a challenge by facing another dolphin, opening its mouth, thereby exposing its teeth, or arching its back slightly and holding its head downward. This behavior is more along the lines of visual communication but still may or may not be accompanied by vocalizations such as burst-pulsed sounds. The burst-pulsed sounds, which are more complex and varied than the whistles, are often utilized to convey excitement, dominance or aggression such as when they are competing for the same piece of food (Janik. 2013). The dolphins also produce these forceful sounds when in the presence of other individuals moving towards the same prey. On the sexual side Caldwell (1977) saw that dolphins may solicit a sexual response from another by swimming in front of it, looking back, and rolling on its side to display the genital region. These observations provide yet another example of visual communication where dolphins exhibit different postures and non-vocal behaviors to communicate with others that also may or may not be accompanied by vocalizations. Sexual selection for greater variability, and thus in turn vocal learning, may then be a major driving force for the evolution of vocal learning. Rapid adaptation to sound transmission in different environments may be a likely contributor to vocal learning evolution. Vocal non-learners produce their sounds best in specific habitats, making them more susceptible to changes in the environment. For example, pigeons' low-frequency calls travel best near the ground, and so communication higher in the air is much less effective (Jarvis. 2009). In contrast, vocal learners can change voice characteristics to suit their current environment, which likely allows for better group communication. For example, many experiments have been done on dolphin mimicry. One such study done by McCowan (1997) showed that dolphins can imitate human made noises in their environments such as electronically produced whistles which may then be added to their repertoire of sounds. It is unclear as to whether or not these new sounds are simply mimicked or if they are essentially given meaning (King. 2013), but there is definitely some transfer of information that may be a good evolutionary factor. An alternative hypothesis suggests there may be a correlation between predation and evolution of vocal learning. The hypothesis proposes that predatory pressure applies a strong selective force against vocal learning. If mates prefer more variable vocalizations, predators may also be more strongly attracted to more variable vocalizations. As innate calls are typically constant, predators quickly familiarize to these vocalizations and ignore them as background noise (Jarvis.2009). In contrast, the variable vocalizations of vocal learners are less likely to be ignored, possibly increasing the predation rate among vocal learners. In the latter case, some system would eventually have to develop in order to compensate for the increase in predation and facilitate the evolution of vocal learning. Supporting this hypothesis is the fact that many mammalian vocal learners including dolphins, humans, whales, and elephants have very few major predators (Tyack. 2008). While little research has been done in this area, some studies have supported the predation hypothesis. Although these studies are promising, more research is needed in this area to compare predation rates across vocal learners and non-learners. In conclusion, even though there are many propositions as to how vocal learning evolved, it is still unclear as to what particular cause is responsible. It is possible that there may be multiple causes such as a combination of the above mentioned hypotheses or even other unknown factors. More research is needed that looks into the vocal mechanisms of dolphins and their evolutionary significance in order to get a better understanding of dolphins and their communication.

1) Janik, Vincent M (06/2013). "Communication in bottlenose dolphins: 50 years of signature whistle research". Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology (0340-7594), 199 (6), p. 479. This article reviews the history of signature whistles and how these signals stand out amongst recognition calls in animals and how they contribute to our understanding of complexity in animal communication.

2) King, Stephanie L (04/22/2013). "Vocal copying of individually distinctive signature whistles in bottlenose dolphins". Proceedings of the Royal Society. B, Biological sciences (0962-8452), 280 (1757), p. 20130053. This article looks into the function of vocal copying in a mammal that shows vocal learning as well as complex cognitive and social behaviour, the bottlenose dolphin.

3) McCowan, Brenda (1997). "Vocal learning in captive bottlenose dolphins: A comparison with humans and nonhuman animals" in Social Influences on Vocal Development (0-511-75884-7, 978-0-511-75884-3), (p. 178). Cambridge: Cambridge University Press. This article examines bottlenose dolphins as a prime model to investigate the processes of vocal learning and mimicry in nonhuman animals.

4) Podos, Jeffrey (07/2002). "Vocalizations of Amazon River Dolphins, Inia geoffrensis: Insights into the Evolutionary Origins of Delphinid Whistles". Ethology (0179-1613),108 (7), p. 601. This article examines the vocalizations of amazon river dolphins and looks into the evolutionary basis of delphinid whistles.

5) Tyack, Peter L (08/2008). "Convergence of calls as animals form social bonds, active compensation for noisy communication channels, and the evolution of vocal learning in mammals". Journal of comparative psychology (1983) (0735-7036), 122 (3), p. 319. This article looks into the wide taxonomic distribution of evidence for vocal production learning and examines the possibility that there may be more neural underpinnings for vocal production learning in place in mammals than is usually recognized.

https://en.wikipedia.org/wiki/Vocal_learning
1) This article could cover a bit more on the vocal learning in other animals such as dolphins instead of focusing on mainly birds. 2) This article could incorporate more anatomical and/or physiological explanations to vocal learning. 3) This article could touch on more comparisons between different species and their vocal learning style. --Ector.6 (talk) 02:05, 2 October 2014 (UTC)
Comparative studies indicate that whistles vary in structure across populations and species (Steiner 1981; Ding et al. 1995; Rendell et al. 1999), with whistle divergence perhaps facilitating species recognition and speciation (Podos et al. 2002).