Data from: Risk allocation in a freshwater gastropod

To balance the basic needs of organisms, internal and external cues are
used to inform the optimal behavioral strategy. Some of the best-studied
related cognitive rules have emerged in predator-prey contexts, such as
the threat-sensitivity hypothesis, which postulates that prey should
adjust their antipredator behavior in accordance with the level of risk.
Extending this theory, the risk allocation hypothesis posits that under
long-term sustained high predation risk, individuals should decrease their
antipredator responses towards risky stimuli so as to meet their energetic
demands. Evidence for the risk allocation hypothesis has been mixed in
invertebrates, particularly in gastropods that are classic model systems
for antipredator responses. This may be due to past studies frequently
lacking sham controls and/or sufficient certainty about the risk regime.
The present study in the aquatic gastropod Physella acuta controls for
these factors by crossing long-term background risk, i.e., lifelong
consistent exposure to conspecific alarm cues (high-risk), a reliable cue
of high predation risk, or a water control (low-risk), with exposure to a
high-risk or low-risk stimulus. Crawl-out behavior is an adaptive
antipredator response in gastropods. In accordance with
threat-sensitivity, high-risk stimuli induced increased crawl-out behavior
independent of background risk. Providing partial support for risk
allocation, high background risk induced lower responsivity to both
low-risk and high-risk chemical stimuli. This may be because cue addition
also provided tactile cues that could be considered risky by high
background risk snails. Altogether, the present well-controlled research
contributes novel data to the hitherto mixed evidence for risk allocation
in gastropods.