| Summary: | Macrocystis represents the most widely distributed kelp genus, providing structure and energy for one of the most productive ecosystems on earth. Despite its ecological and economical importance, many aspects of its taxonomy, distribution and dispersal still remain unknown. Using different molecular markers I studied the taxonomy, phylogeography and dispersal patterns of Macrocystis. The analysis involves samples from different populations throughout the world. Using the DNA barcoding method I, confirmed previous suggestions that the genus must be considered as monospecific, M. pyrifera being the only species. The effects of historical and contemporary events on the haplotype distribution were determined by analyzing samples from the southeastern Pacific (SEP) using the atp8-S mitochondrial marker. The last glacial maximum as well as oceanographic anomalies (El Niño phenomena) may be important factors driving the genetic pattern along the SEP. The genetic structure in southern Chile was also analyzed in more detail, especially in the Chilean Fjords. Samples from attached and floating kelp individuals revealed that dispersal via kelp rafts is possible. Finally, a global analysis using COI sequences showed shared haplotypes along vast distances in the Northern and Southern hemispheres, recent dispersal and high gene flow can explain such genetic homogeneity. Additionally, microsatellite analysis confirmed that gene flow along the Southern Ocean is occurring over ecological time scales, where rafting of detached reproductive kelps seems to be facilitated by the Antarctic Circumpolar Current connecting populations in the Southern Hemisphere. This study has provided valuable genetic evidence to understand factors shaping the genetic structure of this important ecologically and economically species. It also contributes important knowledge for conservation and management strategies, especially in places where M. pyrifera has been harvested. In summary, the results of this study confirm previous suggestions of high gene ...
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