Temperature effects on survival and dormancy patterns across age groups in vulnerable land snail Vertigo moulinsiana

The Desmoulin's whorl snail, Vertigo moulinsiana (Dupuy, 1849) (Gastropoda: Vertiginidae), an endangered micro-mollusc listed as Vulnerable in Annex II of the EU Habitats Directive, uses aestivation to survive environmental stress. This study aims to evaluate the effects of constant versus fluctuating thermal regimes on survival and activation dynamics of V. moulinsiana. Specimens from each age group individually (juveniles, subadults, adults distinguished based on the number of shell whorls and the presence of apertural barriers) were subjected to six thermal treatments: 23 °C, 35 °C, fluctuations between 25 °C and 35 °C, 4 °C, fluctuations between 4 °C and - 10 °C, and - 10 °C. Study shows that juveniles exhibited the lowest survival rates under low-temperature treatments, whereas adults displayed the tolerance to cold spells. Subadult survival was not significantly influenced by any temperature. Juveniles showed also higher survival under high-temperature treatments. However, due to sensitivity to desiccation, these temperatures must occur with suitable air humidity. Importantly, temperature fluctuations substantially sped up activation time across all the age groups, whereas constant temperatures led to bet-hedging response. Given the increasing frequency of extreme climate events under ongoing climate change, these results suggest even increased vulnerability of this species. Understanding its responses to environmental stress is therefore critical for getting to know protection strategies for V. moulinsiana.