Variation in thermal tolerance response associated with geographic location during early development of the neogastropod Ocenebra erinaceus (Linnaeus, 1758)

Environmental temperature plays an important role in shaping the distribution and abundance of marine ectothermic organisms. As a general rule, larvae and juveniles are more sensitive to thermal stress than adults and, as a consequence, represent key life stages that determine in part the geographic range of a species. Identifying critical thermal limits during ontogeny allows for the prediction of the potential impacts of climate warming on the distribution of marine ectotherms. However, thermal tolerance - and therefore the potential to meet the challenge of warming- is known to vary at population scale for many species. In order to fully appreciate a species' future under climate warming, multiple populations studies from different thermal environments are necessary. In this study, we compared the thermal tolerance response during the intracapsular development of the marine gastropod Ocenebra erinaceus between two geographically separated populations: one from the middle (Solent, UK) and another from the south of the species' geographic range (Arcachon, France). The results show that the thermal tolerance response was influenced by geographic origin. Embryos from the relatively warm-water southern population (France) show a warm-eurythermal tolerance window with optimal temperatures between 12 and 18 °C. On the contrary, embryos from the cold-water northern population (UK) exhibit a narrow, warm-stenothermal, thermal tolerance window with optimal temperatures between 14 and 16 °C. In both populations, temperatures outside of the thermal range cause lethal and sub-lethal effects. Importantly, previously observed dispersal polymorphism was not observed at hatching time in either population in our study. Our study demonstrates that during early developmental stages, embryos are adapted to local thermal conditions and that they live very close to their upper thermal limits. Temperatures outside this range cause detrimental and contrasting effects on embryonic development of O. erinaceus, implying that the effects of future warming will depend on the population response to local environmental history. Our results suggest that global warming could shift the geographical distribution range of O. erinaceus poleward.