Feral frogs, native newts, and chemical cues: identifying threats from and management opportunities for invasive African Clawed Frogs in Washington state.

Abstract

Invasive species threaten biodiversity globally. Amphibians are one of the most threatened vertebrate taxa and are particularly sensitive to invasive species, including other amphibians. African clawed frogs (<i>Xenopus laevis</i>) are native to Southern Africa but have subsequently become invasive on multiple continents-including multiple parts of North America-due to releases from the pet and biomedical trades. Despite their prevalence as a global invader, the impact of <i>X. laevis</i> remains understudied. This includes the Pacific Northwest of the USA, which now hosts multiple expanding <i>X. laevis</i> populations. For many amphibians, chemical cues communicate important information, including the presence of predators. Here, we tested the role chemical cues may play in mediating interactions between feral <i>X. laevis</i> and native amphibians in the Pacific Northwest. We tested whether native red-legged frog (<i>Rana aurora</i>) tadpoles display an antipredator response to non-native frog (<i>X. laevis</i>) or native newt (rough-skinned newts, <i>Taricha granulosa</i>) predator chemical stimuli. We found that <i>R. aurora</i> tadpoles exhibited pronounced anti-predator responses when exposed to chemical cues from <i>T. granulosa</i> but did not display anti-predator response to invasive <i>X. laevis</i> chemical cues. We also began experimentally testing whether <i>T. granulosa</i>-which produce a powerful neurotoxin tetrodotoxin (TTX)-may elicit an anti-predator response in <i>X. laevis</i>, that could serve to deter co-occupation. However, our short-duration experiments found that <i>X. laevis</i> were attracted to newt chemical stimuli rather than deterred. Our findings show that <i>X. laevis</i> likely poses a threat to native amphibians, and that these native species may also be particularly vulnerable to this invasive predator, compared to native predators, because toxic native newts may not limit <i>X. laevis</i> invasions. Our research provides some of the first indications that native Pacific Northwest species may be threatened by feral <i>X. laevis</i> and provides a foundation for future experiments testing potential management techniques for <i>X. laevis</i>.