Etude temporelle a l'aide de marqueurs moleculaires de la diversite genetique et de la conservation des populations de saumon Atlantique, ouananiche (Salmo salar Linne) du Lac Saint-Jean (French and English text)

In this thesis, I present my research on population genetic of landlocked Atlantic salmon populations or ouananiche (Salmo salar ) in Lake Saint-Jean. I documented the genetic structure of these populations, the temporal stability of this structure, the factors that may have affected it and the origin of the different populations. One of the practical objectives of this thesis was the evaluation of current measures of conservation and the elaboration of tools utilisable for long term management. Different molecular approaches as the allozyme analysis, the mitochondrial DNA and the loci microsatellites, were used. It turned out that the last two methods were the most powerful to address our research objectives. The analysis of mt DNA and microsatellites allowed to assess that salmon that reproduced in the four main tributaries of Lake Saint-Jean represented genetically distinct populations. These analysis also allowed to note that the supportive breeding programme causes genetic perturbations on wild populations. These effects were noticeable on the number and frequency of observed alleles, on the genetic divergence and on the effective sizes of some populations, after only one generation of fish produced in hatchery. We concluded also that the high genetic differences noted between the populations were not due to a stochastic effect or to demographic perturbations. The population structure was stable in time for the three to five studied generations. The high genetic divergence among the landlocked populations may be explained by a multiple invasions of the different rivers following the last glacial retreat (probably one ancestor but colonisation in two different time), a more important genetic drift and a restrict gene flow. These results allowed to optimise tools for long term efficient management. The results also allowed to increase the fundamental knowledge about population structure of landlocked Atlantic salmon and to improve the conservation measures in order to preserve the genetic integrity of wild populations.