About the Cover
Cover
Tritonia diomedea is a nudibranch that lives in the shallow northeast Pacific. Within scuba depths, these large slugs (up to 30 cm in length or more) are found exclusively in beds of their prey, the pennatulacean soft corals Ptilosarcus gurneyi and Virgularia sp. (sea pens and sea whips respectively). Tritonia's brain, which has color-coded neurons with stereotyped positions, has been the target of many studies linking neural activity and behavior. Experiments have used simultaneous intracellular recordings from multiple neurons, during apparently normal behaviors in minimally restrained animals, to understand the neuroethology of crawling, feeding, and escape swims, among other behaviors. However, until now there has been no comprehensive field study of Tritonia's behavior.
On pages 81-96 in this issue, Russell C. Wyeth and A. O. Dennis Willows remedy this deficit, presenting a survey of behavior and the slugs' sensory world in their natural habitat, using time-lapse video and scuba. From these observations, the authors formulated new hypotheses about how Tritonia navigates. In a second article (pages 97-108), they enlist the help of Owen M. Woodward to test these hypotheses and conclude that the slugs are presumably using odors from prey, conspecifics, and predators to mediate crawling relative to flow direction: slugs crawl upstream towards food or mates, and downstream away from predators. These results will form the basis for further work on the neuroethology of animal navigation.
On the cover, an active individual of Tritonia is shown with rhinophores and oral veil extended as it crawls across the soft substratum of a sea pen bed. Below are frames (read left to right) from two videos shot in the same habitat. In the black-and-white sequence, a slug executes a rapid (for a slug) bite-strike to feed on a sea pen, which retracts into the sediment in response. In the color sequence, a slug reacts to a predator-the voracious sunflower star Pycnopodia helianthoides-with an escape swim. These swims rely on flow to move the slug away from the predator, and can be triggered by a touch from the predator or by just sensing one upstream. The swim terminates adjacent to a second slug caught in the act of striking a sea pen.
Credits: Photo and videos, R. C. Wyeth and O. M. Woodward (University of Washington); cover layout, Beth Liles (Marine Biological Laboratory).
The feeding video is available in the online supplementary material "(http://www.biolbull.org/supplemental/")
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Copyright © 2006 by the Marine Biological Laboratory.
