Keep your feet warm? A cryptic refugium of trees linked to a geothermal spring in an ocean of glaciers.

Up to now, the most widely accepted idea of the periglacial environment is that of treeless ecosystems such as the arctic or the alpine tundra, also called the tabula rasa paradigm. However, several palaeoecological studies have recently challenged this idea, that is, treeless environments in periglacial areas where all organisms would have been exterminated near the glacier formed during the Last Glacial Maximum, notably in the Scandinavian mountains. In the Alps, the issue of glacial refugia of trees remains unanswered. Advances in glacier reconstructions show that ice domes did not cover all upper massifs, but glaciers filled valleys. Here, we used fossils of plant and malacofauna from a travertine formation located in a high mountain region to demonstrate that trees (Pinus, Betula) grew with grasses during the Lateglacial-Holocene transition, while the glacier fronts were 200-300 m lower. The geothermal travertine started to accumulate more than 14,500 years ago, but became progressively more meteogene about 11,500 years ago due to a change in groundwater circulation. With trees, land snails (gastropods) associated to woody or open habitats and aquatic mollusc were also present at the onset of the current interglacial, namely the Holocene. The geothermal spring, due to warm water and soil, probably favoured woody glacial ecosystems. This new finding of early tree growth, combined with other scattered proofs of the tree presence before 11,000 years ago in the western Alps, changes our view of the tree distribution in periglacial environments, supporting the notion of tree refugia on nunataks in an ocean of glaciers. Therefore, the tabula rasa paradigm must be revisited because it has important consequences on the global changes, including postglacial plant migrations and biogeochemical cycles.

Temporal speciation pattern in the western Mediterranean genus Tudorella P. Fischer, 1885 (Gastropoda, Pomatiidae) supports the Tyrrhenian vicariance hypothesis.

The land snail genus Tudorella shows a peculiar disjunct distribution around the western Mediterranean coasts. Despite high phenotypic plasticity, only two species with a disputed number of subspecific taxa are currently recognised. We delimited the species with mitochondrial (COI & 16S) and nuclear (ITS-1) markers based on the unified species concept and suggested that there are eight species in the genus, two of them currently undescribed. Applying Bayesian phylogenetic model selection, we tested four different biogeographic hypotheses that could be causal for the current distribution pattern of extant Tudorella species. A scenario involving vicariance events resulting from the repeated splits of the Tyrrhenian plate with subsequent dispersal events over land bridges during the Pliocene received greatest support in the data.

Evidence for survival of Pleistocene climatic changes in Northern refugia by the land snail Trochoidea geyeri (Soós 1926) (Helicellinae, Stylommatophora).

BACKGROUND: The study of organisms with restricted dispersal abilities and presence in the fossil record is particularly adequate to understand the impact of climate changes on the distribution and genetic structure of species. Trochoidea geyeri (Soós 1926) is a land snail restricted to a patchy, insular distribution in Germany and France. Fossil evidence suggests that current populations of T. geyeri are relicts of a much more widespread distribution during more favourable climatic periods in the Pleistocene. RESULTS: Phylogeographic analysis of the mitochondrial 16S rDNA and nuclear ITS-1 sequence variation was used to infer the history of the remnant populations of T. geyeri. Nested clade analysis for both loci suggested that the origin of the species is in the Provence from where it expanded its range first to Southwest France and subsequently from there to Germany. Estimated divergence times predating the last glacial maximum between 25-17 ka implied that the colonization of the northern part of the current species range occurred during the Pleistocene. CONCLUSION: We conclude that T. geyeri could quite successfully persist in cryptic refugia during major climatic changes in the past, despite of a restricted capacity of individuals to actively avoid unfavourable conditions.

Active and passive dispersal of an invading land snail in Mediterranean France.

1. Land snail dispersal abilities are considered poor; however, the current invasion of the French Mediterranean region by Xeropicta derbentina (Krynicki 1836), as well as the past invasions of this region by several other species, seems to contradict this view. 2. Using a multilevel approach, from individual experimentation to landscape analysis, the dispersal abilities and mechanisms allowing the passive dispersal of X. derbentina are studied. 3. The colonization of Provence occurred by stratified diffusion, where short-range active dispersal occurs side by side with long-range passive dispersal. 4. Active dispersal is not as limited as previously thought. In the field, the capture-mark-recapture method recorded a maximum distance covered of 42 m in 6 months within a radius of 38 m from the original release point. 5. Temperature and humidity, and therefore the time of year, influence the main type of dispersal. Dispersal is active during wet periods and essentially passive in dry and hot months. 6. Heat avoidance behaviour is one of the mechanisms allowing passive dispersal. 7. Passive dispersal via human activities is the main determinant of X. derbentina distribution within the landscape. In comparison to other species, X. derbentina is found more often in the vicinity of a communication route. 8. These results show that land snails can cover large distances in a lifetime. The potential for active and passive dispersal described in this paper enables X. derbentina to be a successful invasive species and explains the rapid spread and current distribution of this species.