Integrating fossil data, vegetation modelling and genetic analyses of modern tree populations to reconstruct the history of Larix in Europe

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The aim of the proposed project is to study the consequences of past climatic changes on European Larix populations by integrating palaeoecological and genetic data as well as spatial modelling. Such retrospective approaches can help evaluate and calibrate models simulating human-induced climate change on tree distribution. A limitation of current studies dealing with forest trees is that they do not truly integrate, in a quantitative way, the different types of data, which are typically displayed and analyzed separately; In this study, we propose to use statistical approaches based on coalescent modelling to test hypotheses for the past demography and evolutionary history of tree populations. The coalescent modelling will rely on multilocus nuclear DNA information, with palaeoecological data and single locus genetic data (from chloroplast and mitochondria) representing extrinsic information that help frame a priori hypotheses. These multiple hypotheses will then be compared using an information theoretic approach. Trees present several advantages for such studies. In particular, they have left an abundant fossil record (bolh macrofossils and pollen) that can be used to reconstruct their past distribution with great precision. Among trees, Larix decidua is of special interest as it played an important role in the plains of north-central Europe during the first interstadials of the last ice age, and it is still represented in the lowlands of Poland by a group of differentiated populations whose status is unclear, often considered as a ditTerent subspecies (Larix decidua subsp. polonica). These lowland populations must have experienced a different demographical history than the populations from the remaining ofthe range, which have mainly expanded along altitudinal gradients during the Late glacial and the Holocene. As a consequence, larch appears to be a suitable model for our integrative approach. We will focus on the location of glacial refugia and range changes during the Weichselian and the Holocene. The projected palaeoecological and molecular genetic analyses will enable detailed inferences on the demography and evolution ofthe populations ofthis species, using precise quantitative approaches instead of adhoc interpretations.