Genetic structure of the giant kelp Macrocystis pyrifera along the southeastern Pacific

We assessed the genetic structure of the giant kelp Macrocystis pyrifera across a broad latitudinal range along the southeastern Pacific coast (SEP). Specifically we analyzed the concordance of putative biogeographic breaks with genetic discontinuities and the effect of historical and contemporary events on the genetic pattern of this important seaweed. Mitochondrial DNA and single-strand DNA conformation polymorphism (SSCP) analysis for a total of 730 samples were carried out. Only 5 haplotypes were found among individuals collected along 4800 km of coastline, with very low haplotype diversity and a shallow genealogy compared with other macroalgal species. Some phylogeographic disjunctions in M. pyrifera were found to correspond roughly to established biogeographic breaks. On the southern coast we found a genetic break at 42 degrees S (Chiloe Island) coincident with a well-known biogeographic boundary, while the genetic break found between samples in central/northern Chile (33 degrees S) does not correspond to any known biogeographic breaks in other brown algae, but does reflect a break associated with other marine taxa. The low genetic diversity in northern Chile may be related to contemporary events (e.g. El Nino Southern Oscillation) while in southern Chile the haplotype distribution may reflect the effect of historical events (Last Glacial Maximum; LGM). Additionally, we compared the SEP data with samples from some of the subantarctic islands and New Zealand. The results showed shared haplotypes among some of the subantarctic islands and southern-central Chile, suggesting a recent colonization of the subantarctic region. The high dispersal potential of kelp rafts may also help to explain the low genetic diversity observed. We conclude that both present and historic events are responsible for the genetic structure of M. pyrifera along the SEP.