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University of Puget Sound

Publication Date

Spring 2012

Program Name

Australia: Rainforest, Reef, and Cultural Ecology


Lateralization, or behavioral asymmetry, is the tendency to favor one side of the body over the other, and exists in humans and animals including in mammals, birds, and fishes. It has been found to increase performance in certain behaviors such as escape from predators by lowering reation time. Lateralization has predominantly genetic bases, but can also be influenced by environmental factors. For example, lateralization has been observed to increase in populations of fish subject to high predation pressure as it decreases their response time to predatory attacks. Parasitism may also have important effects on lateralization. In particular, increased drag from large ectoparasitic isopods is thought to reduce swimming performance of fishes and increase vulnerability to predation. Here, we examined whether fish infected with an ectoparasite compensate for a potential decrease in their swimming performance by increasing their degree of lateralization. Specifically, we examined the bridled monocle bream (Scolopsis bilineata), which is parasitized by a large ectoparasitic cymothoid isopod, Anilocra nemipteri, on the Great Barrier Reef. In order to gain insight into host-parasite interactions, we quantified the prevalence of infections in the population of S. bilineata at Lizard Island, on the Northern Great Barrier Reef, Australia. We then examined the effect of A. nemipteri on lateralization patterns in S. bilineata by comparing the turning behavior of unparasitized and parasitized individuals. We found no preference for right or left turns at the group level, but individuals were lateralized in all groups. Individuals were significantly more lateralized in the parasitized group than in the unparasitized group, and removing parasites from infected individuals decreased lateralization, suggesting that parasitism by 4 A. nemipteri has a significant effect on turning behavior. As lateralization has been shown to reduce reaction time in fish and increase the probability of escaping from predators, S. bilineata may compensate for lower fitness and swimming performance due to infection by A. nemipteri by increasing its turning preference to one side.


Behavior and Ethology | Terrestrial and Aquatic Ecology



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