Phylogeography Gene Flow and Population Structure of "Crambe Crambe" (PoriferaPoecilosclerida)

Résumé

The main goal of this thesis has been to study the population structure of a marine sponge species ("Crambe crambe") at different geographic levels using different molecular markers. In many organisms, particularly terrestrials, molecular markers have been used to answer questions about the structure and connectivity of populations, the potential of dispersal or the history of species, and these data were of crucial help in conservation and management of species. Most of these studies used allozymes and, more recently, mitochondrial or nuclear sequences with success. Also, microsatellite markers are being developed and applied with terrific success in many species. Unfortunately, application of molecular markers in marine environments lags much behind, especially for invertebrate organisms, where population genetic studies are still scarce and most of them involve only allozymes. Thus, this study attempts to be contribute to the development and application of molecular markers for ecologic and population genetic studies in marine invertebrates. Most marine invertebrate organisms are benthic, and many of them sessile, with larvae as the main form of dispersal. Because of the intrinsic difficulty on following larval movements in natural environments, molecular markers appear as the perfect tool to track and characterize populations, and even individuals. Hence, in this thesis several molecular markers have been applied in a sponge species, and with the complementary help of previous ecological and biological knowledge of the species, the present-day population structure of this sponge has been studied, trying to uncover which factors are affecting and might have affected in the past the structure found, while comparing the resolution and the snapshot information recovered with each of the markers used.