| Summary: | Macrocystis represents the most widely distributed kelp genus, providing structure and energy for one oft he most productive ecosystems on earth. Despite its eco logica l and economica l importance, many aspects of its taxonomy, distribution and dispersa! still remain unknown. Using different molecular markers 1 studied the taxonomy, phylogeography and dispersa! p~ttern s of Macrocystis. The analysis involves samples from diff erent populations throughout the world. Using the DNA barcoding method 1, confirrn ed previous suggestions that the genus must be considercd as monospec ific, M. pyr!fera being the only species. The effects of historica l and contemporary events on the haplotype d istribution were determined by a na lyzing samp les fi·om the southeastern Pac ific (SEP) using the atp8-S mitochondrial marker. The last glac ial maximum as wel! as oceanographic anoma!ies (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, especia lly in the Chilean Fjords. Samples fi·om attached and floating kelp índívidua ls revealed that dispersa! via kelp rafts is possible. Finall y, a global analysis using COl sequences showed shared haplotypes along vast distances in the orthern and Southern hemispheres, recent dispersa! and high gene flow can explain such genetic homogeneity. Additionally, microsatell ite analysis confinned that gene flow along the Southern Ocean is occurring over ecologica l time scales, where raft ing of detachecl reprocl uctive kelps seems to be fac ilitated by the Antarctic Circumpo lar Current connecting populations in the Southern Hemisphere. This study has provided va luable genetic evidence to understancl factors shaping the genetic structure ofthis ímportant eco logically and economical ly spec ies. lt also contributes important knowledge for conservation and management stratcgies, espec ially in places where M. pyrifera has been harvested. In summary, the results ofthis study confirm previous suggestions of high gene flow among M. pyrifera populations at different sca les. lt also provides evidence suggesting that kelp rafts actas an important dispersalmechanism in this spec ies, thus giving important information to understand the fac tors shaping the evolution ofthe largest seaweed on earth.
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