Anderson D et al. (2024), Feral frogs, native newts, and chemical cues: i...

XB-ART-60695

PeerJ 2024 Jan 01;12:e17307. doi: 10.7717/peerj.17307.

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

Anderson D , Cervantez O , Bucciarelli GM , Lambert MR , Friesen MR .

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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 (Xenopus laevis) 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 X. laevis remains understudied. This includes the Pacific Northwest of the USA, which now hosts multiple expanding X. laevis 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 X. laevis and native amphibians in the Pacific Northwest. We tested whether native red-legged frog (Rana aurora) tadpoles display an antipredator response to non-native frog (X. laevis) or native newt (rough-skinned newts, Taricha granulosa) predator chemical stimuli. We found that R. aurora tadpoles exhibited pronounced anti-predator responses when exposed to chemical cues from T. granulosa but did not display anti-predator response to invasive X. laevis chemical cues. We also began experimentally testing whether T. granulosa-which produce a powerful neurotoxin tetrodotoxin (TTX)-may elicit an anti-predator response in X. laevis, that could serve to deter co-occupation. However, our short-duration experiments found that X. laevis were attracted to newt chemical stimuli rather than deterred. Our findings show that X. laevis 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 X. laevis invasions. Our research provides some of the first indications that native Pacific Northwest species may be threatened by feral X. laevis and provides a foundation for future experiments testing potential management techniques for X. laevis.

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	Figure 1. Map of sites.Map of focal source ponds. ACF are present in high densities in Pond 1, are rare in Pond 2, largely absent from Pond 3, and have not been detected in the ECY pond. Trapping has found chorus frog (Pseudacris regilla) and long-toed salamander larvae (Ambystoma macrodactylum) in Pond 1 and 3. Red-legged frog (Rana aurora)—a relatively urban-sensitive species—breed in Pond 3 in addition to the other native amphibians from Pond 1 and 2, and the ECY pond. Our experimental ACF were sourced from Pond 1, R. aurora embryos from ECY pond, and newts were collected between Ponds 1 and 2.
	Figure 2. Example of newts trapped along fence.Native rough-skinned newts migrating to breed at Ponds 1 and 2 but became stuck along silt fencing meant to limit ACF dispersal from these ponds. In 2022, St. Martin’s students assisted 1,207 newts over the fences so they could breed. Imagery courtesy of Esri (Redlands, CA, USA).
	Figure 3. (A–B) Experimental set up.Chemical cues were extracted from native rough-skinned newts and feral ACF by bathing them in 300 mL of aged tap water for 2 h. Larval R. aurora were then exposed to two mL aliquots of either chemical cue or control water with no amphibian cues.
	Figure 4. Experimental set up.Experimental set up to test whether feral ACF responded to native rough-skinned newt cues. ACF were placed in experimental tanks with two mesh bags: one containing a newt and an empty control bag.
	Figure 5. Time allocation of ACF to treatments.Time spent by ACF away from native, toxic newts in sham controls (Away), next to native newts (Newt), or in the center of experimental tanks. ACF spent the most time next to newts, intermediate amounts of time next to sham controls, and the least amount of time at the center. Boxplots center lines indicate data medians, box edges represent 25th and 75th quartiles, and points are outliers.

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