Abstract

The coast along the temperate South East Pacific (SEP) presents a simple linear topography with a north-south orientation spanning more than 4600 km. However, environmental heterogeneity associated with two major biogeographic boundaries has been described along the SEP (30–33°S and 42°S). Recent phylogeographic studies of seaweeds revealed the existence of different cryptic species along the SEP coast and that most of the genetic breaks between them are broadly congruent with the biogeographic boundaries. These phylogeographic patterns characterized by genetic discontinuities could be attributed to historical vicariance or to budding speciation. For SEP seaweeds, two major phylogeographic patterns are observed. Endemic species living north of 42°S show complex haplotype networks and an almost complete genetic isolation between populations located only a few kilometres from each other. This extreme genetic patchiness has been related to the combined effects of limited dispersal, reduced population size and high population turnover of these intertidal seaweeds due to stochastic effects of climatic and tectonic catastrophes. On the other hand, species with a range distribution limited to the south of 42°S and inhabiting the area highly affected by the coastal ice cap during the Last Glacial Maximum (LGM), show typical signatures of post-glacial demographic expansion. Finally, molecular studies reveal that several species are recent immigrants from New Zealand, demonstrating the importance of oceanic dispersal in shaping the diversity of the SEP.