Present-day connectivity of historical stocks of the ecosystem engineer Perumytilus purpuratus along 4500km of the Chilean Coast

Historical processes leading to the emergence of marine stocks, the mechanisms maintaining stock structure, and present-day connectivity patterns are elementary pieces of information to design wiser and more sustainable management of marine resources, and to understand speciation processes in the sea. Over geographical scales, biological and genetic continuity in the Southern Pacific coast is determined by historical geological-climate events (e.g., LGM), as well as by present oceanographic processes (Humboldt Current, ENSO and others) that can affect both, local adaptation and dispersal. The relative influence of such processes on the current distribution of species can be comprehensibly inferred from a detailed population sampling comprising the whole species range. In this work, we aimed to provide insights into historical and modern patterns of genetic connectivity between stocks of the intertidal mussel Perumytilus purpuratus, a species reported to have moderate pelagic development times of about 14–18 days. To this end, we analyzed the geographical pattern of variation of microsatellite polymorphisms across 17 localities scattered along ca. 4500km off the Chilean Coast and encompassing four biogeographic regions, previously defined based on compositional changes in marine flora and fauna, and which coincide with large changes in topography, the historical influence of glaciation, circulation patterns and upwelling variability around 26°S, 30°S and 40°S. Genetic structural data suggest that historical geological and climatic events have shaped the actual range of this species in the south-eastern Pacific, creating biogeographical limits, i.e., the north-central stock and the southern stock, that moderate to restricted dispersers cannot cross given present day coastal oceanographic processes. Conversely, the pattern of IBD observed within those two major biogeographical regions suggests that present-day coastal processes modulate the effective dispersal of this species.