The Ontogeny of Chemically-Mediated Antipredator Behaviours in Newts (Notophthalmus Viridescens): Responses to Injured and Non-Injured Conspecifics

Abstract

SummaryResponses to alarm chemicals from injured prey may in uence predation risk and foraging success of receivers and senders, while learning can in uence the strength of these responses. Thus, it is important to know when in ontogeny prey produce and detect alarm substances and how learning shapes their response, but surprisingly little is known about either of these topics. We assessed when in the life of red-spotted newts, Notophthalmus viridescens, alarm chemicals are produced and detected by comparing adult versus eft (terrestrial juveniles) and larval responses to rinses and tissue extracts from individuals in each life-history stage. To evaluate the in uence of experience in larvae exposed to conspeci c alarm substances and rinses from adults known to cannibalize larvae, we compared the response of naïve larvae, which had no prior experience with alarm chemicals or predators, to experienced larvae, which were likely to have experienced alarm chemicals and predators in their native pond. Larvae were indifferent to larval rinses and extracts, but reduced their activity in response to adult rinses and extracts. There was no difference between responses of recently hatched naïve and experienced larvae, indicating that larvae exhibit innate antipredator behaviors in response to adult odour. Adults were indifferent to all larval treatments and adult rinse, but avoided adult extract. Since neither adults nor larvae responded to larval extract, larvae did not appear to possess alarm chemicals, and consequently, we were unable to assess the in uence of experience on alarm substance response in larvae. Adults and efts were indifferent to rinses, but avoided extracts from conspeci cs of both life-history stages. Together, these results demonstrate that red-spotted newts do not produce alarm chemicals until late in larval development, but can respond to predation-related chemical cues soon after hatching.

Dryness increases predation risk in efts: support for an amphibian decline hypothesis

“…In contrast to activity, eft directional response to desiccation risk and conspecific extracts was conflicting, supporting the independence or "dissociation" of salamander activity and directional response (Madison et al 1999;Rohr et al 2002b). As hypothesized, efts were attracted to conspecific odors under dry conditions and avoided conspecific extracts under wet conditions, but were indifferent to eft alarm chemicals when at risk of desiccation.…”

“…Predators that consumed newts in the laboratory often ate both adults and efts (Hurlbert 1970). Thus, when adult newts move to terrestrial habitats during the late summer (Hurlbert 1969), efts and adults likely coexist and share predators, potentially providing a benefit for efts to respond to both injured eft and adult newts (Rohr et al 2002b). …”

“…Although we did not quantify eft desiccation or predation rates, on average, mitigating actions were not taken for either threat when combined, suggesting greater desiccation and predation risk, which supports the amphibian decline hypothesis that increased dryness attributed to global climate change exposes amphibians to enhanced biotic threats. Abolished avoidance of alarm chemicals during dry spells is likely common for amphibians, since many species huddle in dry conditions (Wells and Wells 1976), use chemical cues to locate conspecifics (e.g., Rohr et al 2002aRohr et al , 2002b, and respond to damage-release alarm chemicals (Chivers and Smith 1998).…”

“…We predicted that efts exposed to predation-related chemicals released from injured conspecifics would reduce activity and exhibit avoidance because these are typical responses to damage-release alarm chemicals that reduce encounters with predators responsible for injury (Chivers and Smith 1998). Furthermore, heterospecific damage-release chemicals are not avoided by adult newts (Marvin and Hutchison 1995), but conspecific alarm chemicals reduce adult activity (Rohr and Madison 2001) and induce avoidance by adults and efts (Rohr et al 2002a(Rohr et al , 2002b, but adults do not avoid When exposed to simultaneous predation and desiccation risks, we hypothesized a tradeoff between avoidance of conspecific alarm chemicals and attraction to conspecifics. Dryness often induces conspecific attraction in amphibians, facilitating huddling to reduce evaporative water loss (e.g., Gehlbach et al 1969;Heinen 1993).…”

Antipredator pheromones in amphibians: a review

“…Responses to alarm infochemicals from injured prey may influence predation risk and foraging success of receivers and senders, while learning can influence the strength of these responses. Red-spotted newts (Notophthalmus viridescens) do not produce alarm chemicals until late in larval development, but can respond to predation-related chemical cues soon after hatching (Rohr et al, 2002). Two tested species of salaman-der, fire-bellied newts (Cynops pyrrhogaster) and red-spotted newts (Notophthalmus viridescens) avoided chemical alarm cues from a conspecific damaged skin extract.…”