Aim Disentangling the roles of the interacting processes that shape species' ranges requires independent measurements of dispersal, physiological traits and habitat use. Multifaceted approaches of range determinants are, however, still rare, despite the widespread recognition that correlative modelling approaches alone are not sufficient to understand and predict species' distributions. Here, we combined genetic, distributional and physiological data to reveal the processes that cause the disjunct distribution of the groundwater isopod Proasellus valdensis in isolated Alpine mountains previously covered by Pleistocene glaciers.Location The Alps and Jura Mountains, France.Methods Phylogenetic/phylogeographical methods based on mitochondrial and nuclear genes were used to test for recent dispersal between mountains. A logistic regression on presence-absence data was performed to quantify variation in the probability of occurrence with temperature. Variation in survival and respiration over a range of temperatures was measured within four populations to test for a causal effect of temperature on species distribution.Results Despite the disjunct distribution, genetic analyses supported recent dispersal between mountains, as indicated by weak divergence among sequences of cytochrome c oxidase subunit I (COI), a single haplotype network showing no spatial structuring, and a small proportion of molecular variance distributed between mountains. The probability of occurrence of P. valdensis decreased significantly with increasing temperature, although physiological experiments indicated that occurrence in warmer habitats was probably restricted by thermally dependent biotic interactions rather than by temperature itself. All populations maintained a high survival rate over a wide range of temperatures (3-15°C), with a weak but detectable tendency for local adaptation.Main conclusions Combining phylogeographical, physiological and habitat modelling methods reveals the interacting processes that drive range dynamics. A broad thermal tolerance helps P. valdensis to colonize vacant habitats during the onset of glacial melting, but range fragmentation and local adaptation, leading to thermal niche narrowing, proceed during warmer interglacials as biotic interactions progressively intensify.

Whereas the consequences of global warming at population or community levels are well documented, studies at the cellular level are still scarce. The study of the physiological or metabolic effects of such small increases in temperature (between +2°C and +6°C) is difficult because they are below the amplitude of the daily or seasonal thermal variations occurring in most environments. In contrast, subterranean biotopes are highly thermally buffered (±1°C within a year), and underground water organisms could thus be particularly well suited to characterise cellular responses of global warming. To this purpose, we studied genes encoding chaperone proteins of the HSP70 family in amphipod crustaceans belonging to the ubiquitous subterranean genus Niphargus. An HSP70 sequence was identified in eight populations of two complexes of species of the Niphargus genus (Niphargus rhenorhodanensis and Niphargus virei complexes). Expression profiles were determined for one of these by reverse transcription and quantitative polymerase chain reaction, confirming the inducible nature of this gene. An increase in temperature of 2°C seemed to be without effect on N. rhenorhodanensis physiology, whereas a heat shock of +6°C represented an important thermal stress for these individuals. Thus, this study shows that although Niphargus individuals do not undergo any daily or seasonal thermal variations in underground water, they display an inducible HSP70 heat shock response. This controlled laboratory-based physiological experiment constitutes a first step towards field investigations of the cellular consequences of global warming on subterranean organisms.

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