Abstract
Tadpoles detect chemical signals released from predators and conspecifics, as well as those present in the environment, and adjust their behavioral responses. This study evaluated the swimming activity of Dorbigny’s Toad (Rhinella dorbignyi (Duméril and Bibron, 1841)) tadpoles exposed to chemical signals, including cues from a predator fish, the marbled swamp eel (Synbranchus marmoratus Bloch, 1795), and an injured conspecific; sublethal concentration of insecticide cypermethrin; and their combination. Swimming behavior (total distance moved, mean speed, global activity, number of contacts between tadpoles) was evaluated in an individual (1) and groups of different size (3, 5, 7, and 10 tadpoles) using a video-tracking software tool. Predator exposure modified behavioral parameters, reducing encounters with predators and, therefore, mortality. Total distance moved and mean speed increased in trials involving 1 tadpole and 3 interacting tadpoles exposed to injured conspecifics, whereas global activity increased in all group sizes, showing that gregarious tadpoles may be affected by alarm cues and their behavior may be disrupted. The insecticide treatments (alone and combined) increased parameters in all group sizes, causing hyperactivity due to its neurotoxic effect. The different responses observed after exposure to alarm cues and environmental signals in the different group sizes modified the normal behavior and the ecological dynamics of gregarious tadpoles.
Highlights
Signals from predators, injured conspecifics, and pesticide modify the swimming behavior of the gregarious tadpole Rhinella dorbignyi (Anura: Bufonidae)
This study aimed to evaluate the swimming activity in gregarious tadpoles of Rhinella dorbignyi (Duméril and Bibron, 1941) (Anura: Bufonidae) exposed to different signals: a) chemical cues of the predator Synbranchus marmoratus Bloch, 1975, b) alarm cues of an injured conspecific, c) sublethal concentration of a common pesticide that occurs in water bodies, and d) a combination of the chemical stressors at the individual level and in groups of different sizes
The four variables measuring tadpole swimming behavior were significantly altered after exposure to the different chemical signals in all group sizes: 1 (λ = 0.49, F = 2.26, p < 0.006); 3 (λ = 0.51, F = 5.86, p < 0.0001), 5 (λ = 0.037, F =12.2, p < 0.0001, 7 (λ = 0.004, F = 38.8, p < 0.0001), and 10 tadpoles
Summary
Signals from predators, injured conspecifics, and pesticide modify the swimming behavior of the gregarious tadpole Rhinella dorbignyi (Anura: Bufonidae). This study evaluated the swimming activity of Rhinella dorbignyi (Duméril and Bibron, 1941) tadpoles exposed to chemical signals, including cues from a predator fish. Total distance moved and average speed increased in trials involving 1 tadpole and 3 interacting tadpoles exposed to injured conspecifics, whereas global activity increased in all group sizes, showing that gregarious tadpoles may be affected by alarm cues and their behavior may be disrupted. The different responses observed after exposure to alarm cues and environmental signals in the different group sizes modified the normal behavior and the ecological dynamics of gregarious tadpoles. Chemoreception may be one of the most effective sensory modalities for detecting environmental
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