Abstract

Species complex or species presenting deep genealogical splits that distinguish regional sets of populations across their ranges represent a unique system in which to understand the interplay between population structure, phylogeographical divergence and species limits. Indeed, parapatric margin and hybrid zones have been extensively studied to better understand first, the process of population isolation and divergence and second, the factors that limit present-day gene flow and maintain genetic integrity of divergent entities. Because of their unusual life-history features, red algae could represent an interesting group to study factors promoting lineage splitting, geographic isolation and ultimately the development of intrinsic factors limiting gene flow (i.e. reproductive isolation). Indeed, it have been hypothesised that red algae have a high potential to develop rapid reproductive incompatibility and that genetic isolation and speciation could occur at very small spatial scale. Taking advantage of the recent description of three strictly parapatric divergent lineages in the red alga Mazzaella laminarioides along the Chilean coast, the aim of this proposal is to determine the nature and the strength of historical and present-day barriers to gene flow between these three genetic entities. Species’ distribution range covers 28° of latitude (28-56°S, 3,700km) along the South East Pacific. The separation between the lineages has been localized within two 40km-long segments of coastline (38°38’S-38°19’S, between Southern and Central lineages; 32°55’S-32°29’S, between Central and Northern lineages). During this proposal, we aim to address the four following questions: (1) What are the factors that have promoted lineage splitting at the initiation of the divergence process in M. laminarioides ?; (2) What is the level of on-going gene flow between the lineages and what are the genetic characteristics of the two contact zones?; (3) Are the populations within each lineage at equilibrium with regard to migration, mutation and drift?; and (4) What are the mechanisms maintaining genetic integrity in the contact zone?