Evolution of the thermal tolerance in Pleistocene range expansions of aquatic Coleoptera from Mediterranean refugia

The effect of the Pleistocene glacial cycles on the phylogeographic structure of many European species is well understood, but there is little known on what specific factors allow the range expansion of some species and not others, or the evolutionary consequences of these range expansions beyond the origination of neutral phylogeographic or phylogenetic structure. For some groups of western Palaearctic lotic water beetles preliminary data suggest that the widespread European species originated during the Pleistocene from range expansions of narrowly distributed southern species. Published data of the same groups shows that in general these widespread species have wider thermal tolerances than the narrow southern endemics. This suggests that range expansions of some of the widespread taxa could have been driven by changes in the thermal tolerance of southern populations. Alternatively, differences could be local adaptations subsequent to a range expansion, or the change could had occurred previous or subsequent to the expansion itself, without being directly related to it.
With this project we aim to combine phylogeographic, ecological, physiological and biochemical data to contribute to understand the origin of the extant European fauna and the role of Pleistocene glaciations in its diversification. We will study five species groups of two different families (Hydraena gracilis complex, family Hydraenidae, and four groups of genus Deronectes, family Dytiscidae), including one widespread European species and several narrow, southern endemics for which there is published data showing differences in thermal tolerance. We will establish the detailed origin of the widespread species from molecular phylogenies and phylogeographies, and do laboratory experiments to locate as precisely as possible the origin of the shift in thermal tolerance, and its relation to the range expansion. Selected populations of two of the complexes of Deronectes will be used to compare protein expression profiles of specimens subjected to different temperatures using 2-Dimensional electrophoresis. Through protein fingerprinting we will identify the main metabolic pathways involved in the thermal regulation, and the potential differences between the widely and narrowly distributed species. Using the results of a previous project in a related genus (Agabus brunneus cplx) for which a similar approach was used, we will build a EST library to precisely match target proteins involved in thermal tolerance regulation, and attempt to design a test for their level of expression in natural populations under different thermal conditions to map geographical variation in thermal tolerance.

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