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Open Access Publications from the University of California


The International Journal of Comparative Psychology is sponsored by the International Society for Comparative Psychology. It is a peer-reviewed open-access digital journal that publishes studies on the evolution and development of behavior in all animal species. It accepts research articles and reviews, letters and audiovisual submissions.

Volume 25, Issue 1, 2012

Research Article

Evolution of Communication Sounds in Odontocetes: A Review

The evolutional pathway of communication sounds (i.e., whistles) in odontocetes is reviewed using recent acoustic and phylogenetic studies. The common ancestor of Ziphiidae, Inioidea, and Delphinoidea acquired the ability to whistle in the early Oligocene. Subsequently, Pontoporiidae, Phocoenidae, and the genus Cephalorhynchus lost the ability to whistle and evolved narrow-band high-frequency (NBHF) clicks. I hypothesize that sexual selection based on acoustic signaling contributed to the evolution of whistle. However, group size cannot be excluded as the reason for whistle emergence. The event of whistle loss and replacement with NBHF clicks occurred on three independent occasions after killer whale divergence, through the reconstruction of sound-producing organs. Species with whistle loss may use alternative methods to compensate for whistle information, such as tactile communication. Further research on acoustic communication by Ziphiidae, Inioidea, Monodontidae, and the genus Cephalorhynchus is essential to clarify the evolutional pathway of odontocete whistles.

Tactile Contact Exchanges Between Dolphins: Self-rubbing versus Inter-individual Contact in Three Species from Three Geographies

Self-rubbing and social-rubbing (pectoral fin contact between dolphin pairs) were compared for observations conducted on three dolphin study groups: wild dolphin groups in The Bahamas and around Mikura Island, Japan, and a third group of captive dolphins at the Roatan Institute of Marine Sciences, Roatan, Honduras. A primary aim of this research was to determine whether self-rubbing and social pectoral fin rubbing served overlapping functions. Self-rubbing rates were nearly identical between the three study sites, suggesting that site-specific differences (e.g., environmental conditions, substrate, presence of rocks or coral, social grouping) do not affect the rates at which dolphins rub their bodies against non-dolphin objects. The function of self-rubbing is not entirely clear, and likely involves a combination of factors (e.g., play, pleasure), with functions such as hygiene possibly being shared by both self-rubbing and social-rubbing. Rubbing behavior in general (e.g., rates, body parts used) were similar at all three sites for all three species, suggesting that rubbing is an evolutionarily conserved behavior for delphinid species. Still, subtle and individually distinct differences were documented among our study groups with respect to how often and with whom dolphins exchanged pectoral fin contact or engaged in self-rubbing. Site-specific social pressures and predation risks, as well as individual personality might play a role with respect to the expression of an individual’s observed rubbing behavior.

Behavioural Factors Governing Song Complexity in Bengalese Finches

Bengalese finches are the domesticated strain of the wild white-rumped munias. Bengalese finches had been domesticated for over 250 years from the wild strain white-rumped munias and during this period the courtship song became phonologically and syntactically complex. The purpose of this study is to understand proximate and ultimate causes for song complexity in Bengalese finches. Field observation of white-rumped munias in Taiwan suggests that populations of munias show a gradient of song syntactical complexity: when the population has more sympatric species, the population showed less syntactical complexity, suggesting that syntactical complexity does not develop under the pressure for species recognition. Laboratory study of cross-fostering between the two strains revealed that white-rumped munias are more specialized in accurately learning own-strain phonology while Bengalese finches learned equally but less accurately learned phonology of both strains suggesting that Bengalese finches lost species-specific bias to accurately learn own phonology. By a nest-building assay, we found that females work more when stimulated with complex songs but not with simple songs. Taken these evidences together, we suggest that phonological and syntactical complexity in Bengalese finch songs evolved first because domestication freed them from pressure for species recognition based on song characteristics and then sexual selection advanced the complexity. This is enabled by longer song learning period in Bengalese finches. Neural and molecular studies also support the notion that Bengalese finches keep more song plasticity as adult. In conclusion, song complexity in Bengalese finches provides a unique opportunity for integrative study of animal communication.

The Role of Touch in the Social Interactions of Asian Elephants ( Elephas maximus )

In order to successfully engage in social interactions, it is necessary to recognize and respond to the communicative cues provided by the other participants in these interactions. Communicative signals can occur in a variety of sensory modalities, including vision, sound, olfaction, and touch. In this study, we focus on the role of touch in the social interactions of elephants. Both aggressive and nonaggressive tactile behaviors were examined. In all cases, the body parts used to initiate tactile behaviors as well as the body parts that received these tactile behaviors were analyzed. Significant differences were seen in the overall frequency of tactile behaviors initiated and received by each elephant, as well as in the frequency of aggressive and nonaggressive tactile behaviors initiated and received by each elephant. The trunk was the body part most commonly used to initiate and receive tactile behaviors. The influence of several factors on the observed tactile behavior patterns are discussed, including the influence of social rank and movement in the social hierarchy.