As a result of continuing climate change, native ecological communities are more susceptible to the growing range of introduced species which can result in a substantial loss of biodiversity. Characteristics of an ecosystem, from habitat quality to evolutionary history of species, can affect whether an introduced species becomes invasive. The omnivorous red swamp crayfish (Procambarus clarkii) has become invasive throughout many ecosystems resulting in negative impacts to trophic webs and biodiversity. These crayfish are currently recognized as an invasive species in the freshwater streams of the Santa Monica Mountains (Los Angeles, CA, USA). The California newt (Taricha torosa) is a California endemic amphibian that produces a neurotoxin called tetrodotoxin (TTX). However, P. clarkii does not have an evolutionary history with this toxin because their native range is in the southern United States. We tested the effect that TTX from newts could have on P. clarkii to ultimately understand if TTX limits their negative impacts to biodiversity. Previous studies have indicated that TTX from newts can alter behavior of aquatic species.
Results/Conclusions
We quantified P. clarkii predation on aquatic invertebrate larvae in the presence of (i) a newt chemical cue solution made from the effluent of aquatic adult newts, (ii) a high nitrate solution (25 ppm) to mimic environmental pollution in local streams, and (iii) an amphibian chemical cue solution created from the effluent of California tree frogs (Pseudacris cadaverina) that served as a control for potential amphibian cues without TTX. When crayfish feeding behavior was compared across treatments, P. clarkii consumed significantly fewer invertebrate larvae in the presence of the newt chemical cue solution compared to the amphibian and nitrate solutions. We also measured movement of crayfish in a (i) pure TTX solution, (ii) a newt chemical cue solution, and (iii) an amphibian chemical cue solution and found that crayfish moved nearly equal amounts in TTX solution and newt chemical cue solutions. A post-hoc comparison of crayfish movement across each treatment showed that crayfish moved significantly less in the presence of the newt and TTX solutions compared to other amphibian solutions. Overall, these results suggest that the conservation and presence of California newts in native ecosystems can potentially reduce the invasive impacts of crayfish by limiting their consumption of native species and possibly limiting their expansion.