title: Algal endosymbionts in European Hydra strains reflect multiple origins of the zoochlorella symbiosis.
abstract: Symbiotic associations are of broad significance in evolution and biodiversity. Green Hydra is a classic example of endosymbiosis. In its gastrodermal myoepithelial cells it harbors endosymbiotic unicellular green algae, most commonly from the genus Chlorella. We reconstructed the phylogeny of cultured algal endosymbionts isolated and maintained in laboratory conditions for years from green Hydra strains collected from four different geographical sites within Croatia, one from Germany and one from Israel. Nuclear (18S rDNA, ITS region) and chloroplast markers (16S, rbcL) for maximum likelihood phylogenetic analyses were used. We focused on investigating the positions of these algal endosymbiotic strains within the chlorophyte lineage. Molecular analyses established that different genera and species of unicellular green algae are present as endosymbionts in green Hydra, showing that endosymbiotic algae growing within green Hydra sampled from four Croatian localities are not monophyletic. Our results indicate that the intracellular algal endosymbionts of green Hydra have become established several times independently in evolution.
authors.affiliation: Department of Biology, Division of Zoology, Faculty of Science, University of Zagreb, HR-10 000 Zagreb, Croatia.
authors.forename: Nives
authors.initials: N
authors.lastname: Rajević
authors.affiliation: Department of Biology, Division of Zoology, Faculty of Science, University of Zagreb, HR-10 000 Zagreb, Croatia.
authors.forename: Goran
authors.initials: G
authors.lastname: Kovačević
authors.affiliation: Department of Biology, Division of Zoology, Faculty of Science, University of Zagreb, HR-10 000 Zagreb, Croatia.
authors.forename: Mirjana
authors.initials: M
authors.lastname: Kalafatić
authors.affiliation: Institute of Molecular Evolution, Henrich-Heine University, 40225 Düsseldorf, Germany.
authors.forename: Sven B
authors.initials: SB
authors.lastname: Gould
authors.affiliation: Institute of Molecular Evolution, Henrich-Heine University, 40225 Düsseldorf, Germany.
authors.forename: William F
authors.initials: WF
authors.lastname: Martin
authors.affiliation: Department of Biology, Division of Zoology, Faculty of Science, University of Zagreb, HR-10 000 Zagreb, Croatia. Electronic address: damianf@biol.pmf.hr.
authors.forename: Damjan
authors.initials: D
authors.lastname: Franjević
mesh_terms: D000818:Animals; D002467:Cell Nucleus / Q000235:genetics; D002708:Chlorella / Q000235:genetics*; D002736:Chloroplasts / Q000235:genetics; D021901:DNA, Intergenic / Q000235:genetics; D006829:Hydra / Q000235:genetics*; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D013045:Species Specificity; D013559:Symbiosis / Q000235:genetics*
chemical_list: D021901:DNA, Intergenic; D012336:RNA, Ribosomal, 16S
keywords: Endosymbiotic algae; Green Hydra; Molecular phylogeny; Symbiosis; Taxonomy