Department of Ecology and Evolutionary Biology
University of California, Los Angeles
621 Charles E. Young Drive South
P.O. Box 951606
Los Angeles, CA 90095-1606
rferrer [at] ucla [dot] edu
Ecological interactions and the organismal behaviors that determine their outcomes are dynamically mediated by sensory systems. Relationships between community members and the physiological mechanisms that govern them provide opportunities to examine the effects that sensory information can have at cellular, organismal, population, and community levels. Presently, my focus lies in predator-prey interactions facilitated by chemical communication. Both predator and prey often rely on chemical cues to successfully locate and capture or escape and hide from one another.
Currently I am studying a cannibalistic relationship between adult California newts (Taricha torosa) and their larval prey in freshwater streams. Larval newts exhibit anti-predator responses when exposed the chemical defense compound, tetrodotoxin (TTX), present in adult skin. This toxin is present in a wide variety of vertebrate and invertebrate taxa, but rarely has been identified as an olfactory cue. The larval alarm response to TTX is suppressed when earthworms, alternative adult prey are present. We have identified the basic amino acid arginine, present at a high concentration in earthworm tissues, as the suppressant as using TTX/arginine solutions in laboratory bioassays. Both TTX and arginine possess a guanidinium group that is important in binding interactions, and may competitively bind at olfactory neuron receptors. Subsequent bioassays using structural analogs of arginine with TTX further support this hypothesis.
Adult newts also use olfactory cues to successfully locate prey. In a series of field experiments, free-ranging adult newts were exposed to and array of amino acids present in earthworm extract. Arginine was the most stimulatory odorant tested, and subsequent experiments with arginine analogs revealed narrow tuning in behavioral responses.
California newts appear to utilize arginine as an indicator of adult prey presence at both larval and adult life stages. Interestingly, the responses elicited by this compound are quite different depending on newt ontogenetic stages. Arginine acts as a suppressant in larvae and a stimulant in adults. Structural activity data suggest that olfactory receptors are different at these two life stages. Future study will likely focus on the physiological responses to arginine at both larval and adult stages.