title: Divergence within and among Seaweed Siblings (Fucus vesiculosus and F. radicans) in the Baltic Sea.
abstract: Closely related taxa provide significant case studies for understanding evolution of new species but may simultaneously challenge species identification and definition. In the Baltic Sea, two dominant and perennial brown algae share a very recent ancestry. Fucus vesiculosus invaded this recently formed postglacial sea 8000 years ago and shortly thereafter Fucus radicans diverged from this lineage as an endemic species. In the Baltic Sea both species reproduce sexually but also recruit fully fertile new individuals by asexual fragmentation. Earlier studies have shown local differences in morphology and genetics between the two taxa in the northern and western Bothnian Sea, and around the island of Saaremaa in Estonia, but geographic patterns seem in conflict with a single origin of F. radicans. To investigate the relationship between northern and Estonian distributions, we analysed the genetic variation using 9 microsatellite loci in populations from eastern Bothnian Sea, Archipelago Sea and the Gulf of Finland. These populations are located in between earlier studied populations. However, instead of bridging the disparate genetic gap between N-W Bothnian Sea and Estonia, as expected from a simple isolation-by-distance model, the new populations substantially increased overall genetic diversity and showed to be strongly divergent from the two earlier analysed regions, showing signs of additional distinct populations. Contrasting earlier findings of increased asexual recruitment in low salinity in the Bothnian Sea, we found high levels of sexual reproduction in some of the Gulf of Finland populations that inhabit extremely low salinity. The new data generated in this study supports the earlier conclusion of two reproductively isolated but very closely related species. However, the new results also add considerable genetic and morphological complexity within species. This makes species separation at geographic scales more demanding and suggests a need for more comprehensive approaches to further disentangle the intriguing relationship and history of the Baltic Sea fucoids.
authors.affiliation: Department of Biological and Environmental Sciences, University of Gothenburg, Gothenburg, Sweden.|Centre for Marine Evolutionary Biology, University of Gothenburg, Gothenburg, Sweden.
authors.forename: Angelica
authors.initials: A
authors.lastname: Ardehed
authors.affiliation: Department of Biological and Environmental Sciences, University of Gothenburg, Gothenburg, Sweden.|Centre for Marine Evolutionary Biology, University of Gothenburg, Gothenburg, Sweden.
authors.forename: Daniel
authors.initials: D
authors.lastname: Johansson
authors.affiliation: Centre for Marine Evolutionary Biology, University of Gothenburg, Gothenburg, Sweden.|Department of Marine Sciences, University of Gothenburg, Gothenburg, Sweden.
authors.forename: Lisa
authors.initials: L
authors.lastname: Sundqvist
authors.affiliation: Department of Ecology, Environment and Plant Sciences, Stockholm University, Stockholm, Sweden.
authors.forename: Ellen
authors.initials: E
authors.lastname: Schagerström
authors.affiliation: Centre for Marine Evolutionary Biology, University of Gothenburg, Gothenburg, Sweden.|Department of Marine Sciences at Tjärnö, University of Gothenburg, Strömstad. Sweden.
authors.forename: Zuzanna
authors.initials: Z
authors.lastname: Zagrodzka
authors.affiliation: Komarov Botanical Institute of Russian Academy of Sciences, St Petersburg, Russia.
authors.forename: Nikolaj A
authors.initials: NA
authors.lastname: Kovaltchouk
authors.affiliation: Department of Aquatic Resources, Swedish University of Agricultural Sciences, Öregrund, Sweden.
authors.forename: Lena
authors.initials: L
authors.lastname: Bergström
authors.affiliation: Department of Ecology, Environment and Plant Sciences, Stockholm University, Stockholm, Sweden.
authors.forename: Lena
authors.initials: L
authors.lastname: Kautsky
authors.affiliation: Centre for Marine Evolutionary Biology, University of Gothenburg, Gothenburg, Sweden.|Department of Physics, University of Gothenburg, Gothenburg, Sweden.
authors.forename: Marina
authors.initials: M
authors.lastname: Rafajlovic
authors.affiliation: Centre for Marine Evolutionary Biology, University of Gothenburg, Gothenburg, Sweden.|Department of Marine Sciences at Tjärnö, University of Gothenburg, Strömstad. Sweden.
authors.forename: Ricardo T
authors.initials: RT
authors.lastname: Pereyra
authors.affiliation: Centre for Marine Evolutionary Biology, University of Gothenburg, Gothenburg, Sweden.|Department of Marine Sciences at Tjärnö, University of Gothenburg, Strömstad. Sweden.
authors.forename: Kerstin
authors.identifier: http://orcid.org/0000-0003-0176-7986
authors.initials: K
authors.lastname: Johannesson
mesh_terms: D005060:Europe; D044645:Fucus / Q000145:classification / Q000235:genetics*; D005787:Gene Frequency; D014644:Genetic Variation; D005838:Genotype; D018895:Microsatellite Repeats / Q000235:genetics; D009792:Oceans and Seas; D054712:Salinity