Alejandro Martinez Garcia:
The origin of anchialine and marine cave fauna is still a highly debated topic in Evolutionary Biology. Restricted and disjunct distribution and uncertain affinities of some marine cave endemic lineages have favored their interpretation as living fossils, surviving the extinction of their coastal relatives in cave subterranean ecological refugia. Active colonization and ecological speciation to particular cave niches has been alternatively suggested, but the evaluation of that scenario is obscured by the dominance of crustaceans in anchialine habitats, ecologically similar out and inside caves. The main goal of this thesis is to explore the evolutionary processes behind colonization and adaptation to submarine cave ecosystems in the Atlantic Ocean using annelids as a model, mainly when they involved ancestrally interstitial forms. In order to do that, we studied selected lineages of annelids with cave and interstitial representatives, mainly the families Protodrilidae, Nerillidae, Saccocirridae and Scalibregmatidae. The studies combined the characterization of ancestral and cave habitats, with morphological investigations and phylogenetic analyses founded on extensive taxon coverage. The results yielded new data on poorly understood groups of annelids, but also on some more general aspects of regarding colonization and speciation processes to submarine caves. From an annelid evolution perspective, we produced new phylogenetic studies for Protodrilidae (with the description of four new genera), Saccocirridae and Nerillidae, as well as novel results on the character evolution and diversity of these groups. From the more general prospective of the cave colonization, our results highlight the importance of shift of habitats is a crucial process to understand the morphological change observed in certain cave lineages. The most obvious case in represented by crevicular cave lineages with interstitial ancestors, convergently evolving into suspension feeding forms.