Oxygen consumption rate and mobility performance

Respirometric measurements were carried out using the electrode micro-respiration system MRS-8 (Unisense, Aarhus, Denmark), provided with eight, individually-stirred, micro-respiration glass chambers (approximate volume 4 ml). Respirometric chambers were filled with filtered (0.2 μm) and sterilized stream water to reduce the confounding effect of respiration by micro-organisms.

When the assay temperature was reached, the glass chambers, each housing an individual snail (shell length, 3.5–14.1 mm), were sealed and oxygen-concentration was measured. A second measurement was performed after 15 min and the oxygen-consumption rate was extrapolated from the difference between the two measurements. Values of oxygen consumption rate were standardized for snail shell length. For each assay temperature, different groups of 24 specimens were tested.

Mobility performance was tested by snail righting trials performed at each assay temperature. Snails (shell length, 2.6–15.8 mm) were placed individually in small plastic containers with the shell opening facing upwards. After a short period of immobility (less than 30 seconds), probably due to the disturbance caused by handling, this position stimulated an instinctive reaction of the snails to return to the natural crawling position. The time spent for snails to right themselves was recorded and considered as a proxy of snail mobility performance. For each experimental temperature, we tested separate groups of 30 specimens.