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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 21, Issue 1, 2008

Research Article

Preferential Association Among Kin Exhibited in a Population of Atlantic Spotted Dolphins (Stenella frontalis)

While it is widely accepted that dolphins form associations with conspecifics based primarily on similarities in age class and reproductive status, perhaps equally important is the investigation into secondary influences such as kinship. Preferential association among kin is well-researched in numerous terrestrial species, but has only recently been investigated in cetaceans. This study brings another species into the body of work being formed on the influence of relatedness on cetacean relationships. The association indices of 26 individuals with known relatives in a population of Atlantic spotted dolphins, Stenella frontalis, were compiled from encounters in the Bahamas from 2002-2006. Analysis demonstrated that there is preferential association among kin in this population. Mean association indices were found to be significantly higher within families than between families, and there was a positive correlation between relatedness and coefficient of association. Also, the effects of social segregation based on sex and age class, which were evident in the sample population as a whole, were absent in kin dyads.

Manipulation and Tool Use in captive Yellow-Breasted Capuchin Monkeys (Cebus xanthosternos)

In this short report we test, at an individual level, the prediction that tool use abilities and manipulative tendencies should be correlated, derived from hypotheses in the literature which connect them at a cognitive and evolutionary level. We recorded manipulative events of six captive yellow-breasted capuchin monkeys and later compared these results to their performance in a tool using task. The frequency of time each animal was involved with manipulative events was not correlated to the number of tool-using events displayed by them, even when we analyzed the males only (the most frequent manipulators). This result goes against the idea that tool use in Cebus is a product of both manipulative propensities and tendency to use objects. Most likely, the evolution of tool use in Cebus was due to a complex combination of factors, belonging to various behavioral systems, not only to the foraging one.

A Novel Behavioral Test Battery to Assess Global Drug Effects Using the Zebrafish

The zebrafish (Danio rerio) has been at the forefront of neurobiological research and is steadily gaining favor as a model for behavioral applications. The ease of handling, high yield of progeny, and efficient mode of drug delivery make this species a particularly useful model for behavior. Here, we append to the growing body of literature on zebrafish behavior by introducing a novel behavioral battery of tests aimed at identifying drug induced alterations in social and motoric behaviors. In a series of experiments, zebrafish were exposed to MK-801 (0, 2 μM, 20 μM), SFK 38393 (0, 10 μM, 100 μM), and ethanol (0, 0.5%, 1.0%) for one hour and overt locomotor behaviors were scored. Following a one-hour treatment exposure, circling behavior (a thigmotaxic display typical of dysregulated glutamate function) was scored from videotape at specific time points over a 37-minute session. In a separate experiment the zebrafish’s natural tendency to shoal (social display) was analyzed using a novel open-field paradigm that examined fish distribution over quadrants. Most notably, MK-801 (20 μM) significantly increased circling behavior compared to controls. However, shoaling displays were disrupted when zebrafish were exposed to both MK-801 and SKF 38393 (20 μM and 100 μM respectively). Our results, in part, complement existing knowledge about zebrafish behavior following acute drug exposure. Additionally, our novel approach to assessing shoaling behavior, reported here, introduces an alternative view of social/group behavior in the zebrafish that is sensitive to both NMDA and dopaminergic manipulation.

Vigilance in Female Bottlenose Dolphins (Tursiops sp.) Before and After Calving

Previous research has indicated that bottlenose dolphins alternate activity levels between hemispheres while at rest. This rest strategy allows dolphins to maintain continuous vigilance of their external environment. Dolphins in the care of humans exhibit different behaviors while presumably at rest, including floating at the surface, lying at the bottom, and swimming at very slow speeds in stereotyped patterns. Dolphin mothers in the care of humans have been reported to “not rest” and swim continuously for extended periods of time (weeks or even months) when their calves are first born. The current study examined the night-time rest patterns and vigilance of five female bottlenose dolphins before and after parturition. By differentiating between two types of resting behaviors (floating and slow swimming), we found that mothers altered their rest strategy depending on the parturition state. Floating was only observed at high levels preparturition. In contrast, mothers primarily exhibited active swims (a vigilant state) the first two weeks, post-parturition. The remaining six weeks were characterized by a steady increase in slow swimming (a resting, vigilance state). This change in swim behavior may be associated with neonatal development and may allow mothers to sustain high levels of vigilance for extended periods of time. The results of a behavioral test of vigilance indicated that the mothers also increased their vigilance level post-parturition. Mothers sustained their increased response rate over the eight-week post-parturition period, demonstrating that dolphin mothers maintain high levels of vigilance for an extended period of time.