A laboratory investigation into the single, relative and combined effects of environmental stressors on life history traits in the model freshwater gastropod, Lymnaea stagnalis

Human activity is driving biodiversity loss at an alarming rate. Exposure of ecosystems to 
environmental stressors is becoming more prevalent as a result of human activity. The 
effects of multiple stressors (global warming, pollutant mixture and invasive predator cue) 
were assessed using the great pond snail, Lymnaea stagnalis, which has been 
demonstrated as an effective model species for environmental and toxicity tests. Stressors 
were applied singly and in combinations to test the effects on hatching, survival, growth and 
reproductive outputs upon long term exposure (4.5 months). Initially, stressors were applied 
singly at four exposure levels (and a control) with the aim of generating dose-response 
curves. Effects were observed in response to all stressors including at the lowest exposure 
level for the pollutant mixture (0.05 µg/L). Additionally, it was shown for the first time that L. 
stagnalis responds both behaviourally and physiologically towards predator cue from the 
invasive signal crayfish (Pacifasticus leniusculus). Effect levels from the single stressor 
studies were used to select the exposure levels for the multiple stressor study whereby an 
EC10 and EC30 level were used which encompassed low and environmentally relevant 
exposure levels for each stressor (EC10: 20.2 °C, 0.015 µg/L, 10 % cue; EC30: 22 °C, 0.041 
µg/L, 57.5 % cue). Combinations of stressors were applied to investigate the role of 
biological thresholds – the “dominance hypothesis” - and the importance of stressor intensity 
and identity in driving observed physiological responses. The dominance hypothesis
assumes that there are response thresholds so that when one stressor is present at 
sufficiently high levels, the addition of other stressors has little impact. The importance of 
stressor number, stressor identity and stressor intensity can also be encompassed within the 
dominance hypothesis. Here, the dominance hypothesis is partially supported where effects 
observed in response to single stressors did not differ when compared to multiple stressor 
exposures. However, contradicting this theory, additional effects were observed in response 
to the multiple stressor exposures that were not observed in response to single stressor exposures. Overall, there appeared to be a general stress response since effects were 
broadly similar across treatments regardless of the stressor combinations.