Contrasting behavioural responses to concurrent stressors in an aquatic snail: the importance of stress type and combination.

Behaviour is a fundamental parameter for understanding the animal fitness, serving as an indicator of exposure to stressors. In ecosystems, animals often face multiple stressors simultaneously. Their behavioural responses may vary when exposed to individual stressors, whilst synergistic, additive, or antagonistic effects can result from the interaction of multiple stressors. Therefore, it is imperative to conduct studies that take into account the common occurrence of multi-stress scenarios in aquatic ecosystems. We tested the effects of three sources of stress (acidity (A), toxicity with acetone (T) and conspecific chemical cues (S)) on the behaviour of the aquatic snail Potamopyrgus antipodarum (Tateidae, Mollusca). We evaluated the impact of each stressor, as well as in combinations of two or three stressors simultaneously. The highest time to initiate movement was shown by the animals of the low water pH (A) followed by those exposed to the combination of low water pH and acetone exposure (AT). The differences between the time to initiate movement of each treatment with control revealed a marked decrease in the differences for the snails from the conspecific chemical cues (S) and ST treatments, which mean a higher time to initiate movements. It is concluded that behaviour varied depending on the source and combination of stress. While an acid environment and conspecific signals had contrasting effects when applied separately, their simultaneous exposure resulted in no significant impact. This highlights the importance of considering the combined effects of multiple stressors when extrapolating laboratory results to real-world scenarios, where organisms are often exposed to more than one stressor at a time.