FERRER, R.P.*; ZIMMER, R.K.; Univ. of California, Los Angeles; Univ. of California, Los Angeles: When prey becomes predator: an ontogenetic shift in the role of olfaction.

During development, sensory systems undergo changes in cell receptor machinery. Such modifications may alter the way an animal perceives its olfactory environment. Here we investigated a cannibalistic interaction between two discrete life history stages of the California newt (Taricha torosa). The chemical defense compound tetrodotoxin (TTX), in adult newt skin, is recognized by conspecific larvae as an alarm signal. Yet, alarm behaviors are suppressed when TTX is mixed with odors from alternative adult prey. In laboratory assays, newt larvae were exposed to TTX alone, or in binary mixtures with test compounds isolated from invertebrate prey tissues. Larval escape behavior in response to TTX (0.1 μM) was significantly reduced when arginine (0.1 to 0.01 μM) was added. Free-ranging adult newts were exposed to components of prey tissue extracts in the field. Arginine was the most effective feeding attractant, evoking plume-tracking behavior at concentrations as low as 10 nM. A comparable array of arginine analogs and TTX/arginine analog mixtures was tested on adults and larvae, respectively. Adult responses were eliminated by even slight alterations to arginine, such as the addition of a single carbon to the side chain or esterification of the α-carboxyl group. In contrast, larval alarm responses to TTX were inhibited by arginine as well as by analogs maintaining the guanidinium group. Thus, adults were narrowly tuned and larvae broadly tuned to arginine. These combined results show that arginine has opposing effects (inhibitory/stimulatory) on larval/adult newts, and apparently acts on different suites of olfactory receptors in the two life history stages.