ONTOGENIC CHANGES IN CALIFORNIA NEWTS (TARICHA-TOROSA) IN RESPONSE TO CHEMICAL CUES FROM CONSPECIFIC PREDATORS

Many species of aquatic animals rely on chemical cues to assess the risk of predation. Although amphibians are known to have adaptations to avoid predatory fish, little is known about their adaptations that allow them to co-occur with other aquatic vertebrate and invertebrate predators. Adult California newts (Taricha torosa) prey on egg masses and larvae of conspecifics. Larvae use chemical cues to assess the risk of cannibalism. Laboratory studies showed that larvae that are two weeks post-hatching hid in response to chemical cues from adults. Larvae five weeks post-hatching did not respond to conspecific cues regardless of previous exposure to adult cues. Field surveys supported the prediction that small larvae would use refuges more than larvae that are only slightly older. Surveys of natural stream pools showed that newt larvae spent more time in refuge early in the summer than they did later in the summer. This behavioral shift also corresponds to the time of year when adults leave the streams and return to land. Thus, newt larvae showed an abrupt ontogenetic change in their response to conspecific chemical cues. Reduced sensitivity to conspecific risk suggests that large newt larvae are less vulnerable to conspecific adults than small larvae.