Phylogenetics, biogeography and population genetics of the ascidian Botryllus schlosseri in the Mediterranean Sea and beyond.
The wide distribution of the ascidian Botryllus schlosseri along the Mediterranean coasts has been documented since the eighteenth century. However, despite copious documentation, analyses of dispersal modes and genetic profiles were limited to local populations or restricted regions. In order to get a pan-Mediterranean overview, 288 specimens from 11 populations of B. schlosseri from the western and eastern Mediterranean basins were sampled and analyzed using five microsatellite loci and COI sequences. Both molecular markers revealed high polymorphisms, with 182 microsatellites alleles and 54 COI haplotypes. Overall, Fst, Dest, and COI Фptvalues were 0.146, 0.635 and 0.322, respectively, reflecting a high genetic diversity and a significant genetic structure as compared to other B. schlosseri populations worldwide, reflected by substantially higher values for effective number of alleles (Ne) in the Mediterranean. A phylogenetic analysis of the COI sequences resulted in four distinct clades and two molecular operational taxonomic units (OTUs). We recorded a stronger genetic structure among the populations of the eastern basin compared to the western basin (microsatellites Fst=0.217 versus 0.082; COI Фpt=0.416 versus 0.171), suggesting either a restricted connectivity between the basins or a stronger genetic drift in each basin. The occurrence of two OTUs and different ecological conditions may also contribute to this finding. Mean Nei's genetic distance in the eastern Mediterranean populations was more than three times higher compared to the western basin. No correlation was observed between geographic and genetic distances (Mantel test), suggesting that maritime transport is the main dispersal vector of B. schlosseri colonies. The possibility that the Mediterranean is a center of diversity for B. schlosseri, and probably its site of origin, is further discussed.
Israel Oceanography and Limnological Research, National Institute of Oceanography, Tel Shikmona, PO Box 8030, Haifa 31080, Israel; Department of Evolutionary and Environmental Biology, Faculty of Science and Science Education, University of Haifa, Haifa 3498838, Israel. Electronic address: eitanreem@gmail.com.
Eitan
E
Reem
Israel Oceanography and Limnological Research, National Institute of Oceanography, Tel Shikmona, PO Box 8030, Haifa 31080, Israel.
Jacob
J
Douek
Israel Oceanography and Limnological Research, National Institute of Oceanography, Tel Shikmona, PO Box 8030, Haifa 31080, Israel.
Guy
G
Paz
Department of Marine Biology, Faculty of Science, University of Haifa, Haifa 3498838, Israel; Department of Evolutionary and Environmental Biology, Faculty of Science and Science Education, University of Haifa, Haifa 3498838, Israel.
Gadi
G
Katzir
Israel Oceanography and Limnological Research, National Institute of Oceanography, Tel Shikmona, PO Box 8030, Haifa 31080, Israel.
Baruch
B
Rinkevich
D000483:Alleles; D000818:Animals; D001483:Base Sequence; D001499:Bayes Theorem; D003576:Electron Transport Complex IV / Q000235:genetics; D014644:Genetic Variation; D005828:Genetics, Population; D006239:Haplotypes / Q000235:genetics; D008522:Mediterranean Sea; D018895:Microsatellite Repeats / Q000235:genetics; D008928:Mitochondria / Q000235:genetics; D010802:Phylogeny; D058974:Phylogeography; D025341:Principal Component Analysis; D014561:Urochordata / Q000145:classification* / Q000235:genetics*
D003576:Electron Transport Complex IV
COI; Dispersal; Genetic diversity; Microsatellites; Phylogenetic analysis; Species divergence