Prince, J., Nolen, T.G., and Coelho, L. 1998. Defensive ink pigment processing and secretion in Aplysia californica: Concentration and storage of phycoerythrobilin in the ink gland. Journal of Experimental Biology 201: 1595-1613.

The inky secretions of the sea hare, Aplysia californica are toxic to its attackers. Yet, red algae, predominant in the diet of A. californica, are relatively non-toxic. How then, can sea hares utilize and process a non-toxic food source into a chemical anti-predator deterrent?

Various pigments, proteins and other unknown substances constitute the purple ink of A. californica. Digested algal chromatophores consisting of phycoerythrin, a precursor to the pigment phycoerythrobilin, constitute a significant portion of the ink secretion. Additionally, an ink-protein seems to have a synergistic effect with pigments that systematically deflect predators. After circulating in the snail's vascular system, the mixture of phycoerythrin, phycoerythrobilin and ink-proteins then permeate the ink gland, ready for release.

In this study, three dietary regimens were initiated for laboratory-reared A. californica, including red algae, green seaweed or store-bought romaine lettuce. Secretory vesicles were extracted from the ink gland, followed by tests like spectrophotometry, TEM and SEM visualization and immunogold localization of r-phycoerythrin. Neither phycoerythrin nor phycoerythrobilin were toxic, and but an ink-protein seems to work together with algal pigments to cause toxicity. Althouth direct evidence on the virulence of Aplysia's derived ink protein is lacking, individuals fed green seaweed or lettuce did not release ink protein.

To conclude, the algal pigments consumed by the sea hare are not solely responsible for ink toxicity. A. californica produces an ink-protein that may react with pigments from red algae to form a toxic deterrent to predators.

(250 words)

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(posted Jan. 4 2016)