Abstract
Amphibian populations are declining due to a myriad of abiotic and biotic factors, including invasive species and pathogens. In temperate freshwater ecosystems, for example, amphibian populations are threatened by the predation of introduced salmonids. Salmonids not only directly predate upon amphibian eggs and larvae but may also transport deadly pathogens into freshwater systems. Though most research has focused on temperate systems, much less is known about the effects of introduced species in Neotropical streams. We conducted two experiments to investigate the impacts of rainbow trout (Oncorhynchus mykiss) in two Neotropical anurans. First, we assessed the effect of the rainbow trout on tadpole survivorship and morphology in Nymphargus grandisonae, a glassfrog species endemic of the Andes. Tadpoles of N. grandisonae were subjected to three treatments involving the absence of rainbow trout (control) and its presence with different types of chemical cues – kairomones (from rainbow trout) and cue alarms (from tadpole prey); the results show that the presence of rainbow trout affects the larval morphology of this glassfrog. In the second experiment, to test whether rainbow trout is a vector of the pathogenic freshwater mold Saprolegnia diclina (Oomycetes), eggs of Engystomops petersi were placed with infected and uninfected rainbow trout. There was a high mortality rate in the embryos of E. petersi exposed to trout infected with S. diclina. This represents the first evidence that rainbow trout may have a direct negative effect on Neotropical amphibian populations, and thus should be considered a threat. Management programs should be implemented to eradicate trout from Andean rivers, especially in areas with high number of endangered amphibians.
Highlights
IntroductionThe decline of amphibian populations since the 1970s is a complex global phenomenon involving interactions among biotic and abiotic factors that affect amphibians at various stages of their life.[1,2,3,4,5,6] Habitat alteration and destruction, global environmental change, emergent infectious diseases, contaminants, and/or introduced species have been associated with amphibian population declines.[1,4,7,8,9]The impact of alien species is a leading cause of biodiversity loss in freshwater systems,[10] in amphibian populations, which can be driven to extinction.[7,11,12,13] The rainbow trout is one such alien species common in many freshwater ecosystems
Our study shows that rainbow trout have a clear effect on tadpole morphology and functions as a vector of the pathogenic freshwater mold S. diclina
Many studies have reported that when predator cues are perceived, they act as stressors and can have a negative impact amphibian embryos and larvae.[28,30,51,52]
Summary
The decline of amphibian populations since the 1970s is a complex global phenomenon involving interactions among biotic and abiotic factors that affect amphibians at various stages of their life.[1,2,3,4,5,6] Habitat alteration and destruction, global environmental change, emergent infectious diseases, contaminants, and/or introduced species have been associated with amphibian population declines.[1,4,7,8,9]The impact of alien species is a leading cause of biodiversity loss in freshwater systems,[10] in amphibian populations, which can be driven to extinction.[7,11,12,13] The rainbow trout is one such alien species common in many freshwater ecosystems. Native to the Pacific Coast of North America, this fish has been introduced in at least 125 countries globally,[14] where it primarily is used for sport fishing and aquaculture. As a result, this species has become an exemplar of one of the world′s worst invasive alien species.[15,16,17]
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