Navanax - Aplysia interactions

April 7, 2006
From: William G. Wright

Dear Bill,

I have thoroughly enjoyed and appreciated Slug Forum for a long time, now, without properly registering my thanks. Thank you so much for your dedication to this amazing project.

I wanted to post a movie from my lab's web-site that shows a specimen of Navanax inermis attacking an individual of Aplysia californica.

Locality: Chapman University; Orange, Intertidal, California, USA, Pacific, Spring, 2004, Rocky Intertidal. Length: 60 mm. Photographer: Andrew Duarte.

This Navanax was collected by an undergraduate, Erika Fujimoto, from the outer intertidal near Newport Beach, California. This is prime habitat for Aplysia. Andrew Duarte, another undergraduate in my lab, shot this amazing video sequence. Two observations are important here. First, the Aplysia is no bigger than the Navanax. Thus, its chances of survival are relatively small. Second, the Aplysia is naive. That is, it has never been attacked by a Navanax.

We have now staged a wide range of Navanax attacks on Aplysia, and find that the outcome is rarely as certain as this movie suggests. Size is critically important (larger Aplysia almost always escape), but even if the sizes are similar, the outcome varies substantially. Thus, for example, if the Navanax in this case had encountered the Aplysia from the side, the Aplysia would probably have escaped.

Even more interesting is the effect of the experienced of being attacked on Aplysia. Two other undergraduates in my lab, Amanda Rodriguez and Candace Thomas, have now shown that reflex withdrawal reflexes in Aplysia after once being attacked are enhanced by 50-200 percent. Thus, the experience of surviving a Navanax attack causes "sensitization", an increase in the amplitude of defensive withdrawal reflexes. This form of "learning" has been studied for several decades. Surprisingly, however, no one has until now demonstrated that a natural stimulus (researchers use various unnatural stimuli such as electric shock and wire brushes to induce sensitization) can cause sensitization. Candace and Amanda will present their data at this Fall's Society for Neuroscience Conference in Atlanta, and hopefully we'll have the paper ready soon thereafter.

Of course, the gold standard for an ecologist or evolutionary biologist would be to demonstrate that any behavioral change in an Aplysia that has survived a Navanax attack will actually improve the Aplysia's chances of survival in a second attack. We are presently hot on the trail of this gold standard. Notice in the movie that there is a complete lack of a withdrawal reflex in the Aplysia as it first comes into contact with the Navanax. An increase in the sensitivity to such contact would seem to be a likely first line of defense for a once-attacked, twice shy Aplysia. Stay tuned.

Bill Wright
Chapman University
Orange, California

Wright, W. G., 2006 (Apr 7) Navanax - Aplysia interactions. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Bill,
Thanks for this progress report. It's good to find out what research is going on with these fasinating animals which isn't anatomy and phylogeny. Not that there is anything wrong with anatomy and phylogeny but we anatomists can easily lead a blinkered existence without a bit of cross-fertilisation. I must say watching aglajids feed reminds me of a snake swallowing its prey.

I certainly look forward to updates.
Best wishes,
Bill Rudman

Rudman, W.B., 2006 (Apr 7). Comment on Navanax - Aplysia interactions by William G. Wright. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


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