title: Two-step evolution of endosymbiosis between hydra and algae.
abstract: In the Hydra vulgaris group, only 2 of the 25 strains in the collection of the National Institute of Genetics in Japan currently show endosymbiosis with green algae. However, whether the other non-symbiotic strains also have the potential to harbor algae remains unknown. The endosymbiotic potential of non-symbiotic strains that can harbor algae may have been acquired before or during divergence of the strains. With the aim of understanding the evolutionary process of endosymbiosis in the H. vulgaris group, we examined the endosymbiotic potential of non-symbiotic strains of the H. vulgaris group by artificially introducing endosymbiotic algae. We found that 12 of the 23 non-symbiotic strains were able to harbor the algae until reaching the grand-offspring through the asexual reproduction by budding. Moreover, a phylogenetic analysis of mitochondrial genome sequences showed that all the strains with endosymbiotic potential grouped into a single cluster (cluster γ). This cluster contained two strains (J7 and J10) that currently harbor algae; however, these strains were not the closest relatives. These results suggest that evolution of endosymbiosis occurred in two steps; first, endosymbiotic potential was gained once in the ancestor of the cluster γ lineage; second, strains J7 and J10 obtained algae independently after the divergence of the strains. By demonstrating the evolution of the endosymbiotic potential in non-symbiotic H. vulgaris group strains, we have clearly distinguished two evolutionary steps. The step-by-step evolutionary process provides significant insight into the evolution of endosymbiosis in cnidarians.
authors.affiliation: Department of Genetics, SOKENDAI, Yata, Mishima, Shizuoka 411-8540, Japan; Center for Information Biology, National Institute of Genetics, Yata, Mishima, Shizuoka 411-8540, Japan.
authors.forename: Masakazu
authors.initials: M
authors.lastname: Ishikawa
authors.affiliation: King Abdullah University of Science and Technology (KAUST), Computational Bioscience Research Center, Thuwal 23955-6900, Saudi Arabia.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Shimizu
authors.affiliation: Department of Genetics, SOKENDAI, Yata, Mishima, Shizuoka 411-8540, Japan; Center for Information Biology, National Institute of Genetics, Yata, Mishima, Shizuoka 411-8540, Japan.
authors.forename: Masafumi
authors.initials: M
authors.lastname: Nozawa
authors.affiliation: Department of Genetics, SOKENDAI, Yata, Mishima, Shizuoka 411-8540, Japan; Center for Information Biology, National Institute of Genetics, Yata, Mishima, Shizuoka 411-8540, Japan.
authors.forename: Kazuho
authors.initials: K
authors.lastname: Ikeo
authors.affiliation: King Abdullah University of Science and Technology (KAUST), Computational Bioscience Research Center, Thuwal 23955-6900, Saudi Arabia. Electronic address: takashi.gojobori@kaust.edu.sa.
authors.forename: Takashi
authors.initials: T
authors.lastname: Gojobori
mesh_terms: D000818:Animals; D005075:Biological Evolution; D000460:Chlorophyta / Q000145:classification* / Q000235:genetics; D050259:Genes, Mitochondrial / Q000235:genetics; D006829:Hydra / Q000145:classification* / Q000235:genetics; D016013:Likelihood Functions; D010802:Phylogeny; D012337:RNA, Ribosomal, 18S / Q000145:classification / Q000235:genetics; D013559:Symbiosis / Q000235:genetics
chemical_list: D012337:RNA, Ribosomal, 18S
keywords: Chlorococcum; Endosymbiotic potential; Hydra; Mitochondrial genome