Palaeobiodiversity and distribution of Quaternary European continental snails in response to climatic cyclicity

International audienceReconstructing Quaternary palaeoenvironmental changes from continental mollusc assemblages tells us much about who moves and when. Indeed, climatic cyclicity has strongly influenced the fluctuation of species distribution, particularly in northern Europe, a region severely affected by ice cover movements. In northern territories, the distribution of molluscs shows a dramatic decrease in diversity during Glacial times, leaving only a few tolerant species able to withstand low temperatures. Conversely, Interglacial periods are characterized by diverse faunas, including the development of shade-loving taxa, a category whose occurrence is limited to temperate periods. Interglacials show important differences in diversity due to the occurrence of more forest species during some mild periods of the Middle Pleistocene. The development of Quaternary malacological studies provide valuable datasets for identifying the location of refugia during pleniglacial periods and recolonization pathways after phases of rising temperature. The malacological series from northwestern European demonstrate that thermophilous colonizers originate mainly from the Iberian Peninsula and central Europe. Mediterranean species play a secondary role and only reach the northern areas during the optimal phases of some Pleistocene Interglacials. In north-west Europe, Pleistocene forest faunas are richer than the Holocene one. Indeed, the less humid climatic conditions during the Holocene prevented a long-distance malacological recolonization from Central Europe. The lower diversity of western forest fauna compared to central European areas that is recorded since the beginning of the Holocene is a consequence of the position of glacial refuges in the Carpathian Mountains.Quaternary data also provide an assessment of species extinction rates. They allow a direct comparison between past interglacials periods, where environmental changes were exclusively driven by climatic parameters and modern habitats strongly modified by human impact. In northern France, a well-studied region, 11 species become extinct between 600 and 200 kyr ago, all of them being thermophilous mollusc requiring interglacial climatic conditions. Climatic and anthropogenic factors cause range shifts, but over the last two centuries the rate of changes is 18 times greater than during past interglacials and affects mainly xerophilous and aquatic molluscs rather than forest snails