In 19 vertebrates, 26 IFITM10 genes were identified, covering species from teleosts to eutherians (Fig. 2C ). Each terrestrial vertebrate we surveyed possesses one IFITM10 gene, implying that no gene duplication occurred during the evolution of terrestrial vertebrates. In semi-aquatic frog, one IFITM10 and four IFITM10-like genes were identified. In aquatic vertebrates, three and two IFITM10 or IFITM10-like genes were identified in fugu and medaka, respectively. These indicate that species-specific gene duplications occurred in lower vertebrates. Within the IFITM10 clade, two groups were observed. One includes four IFITM10-like genes from frog and various numbers of IFITM10like genes from teleosts. The other one comprises the frog IFITM10 gene and all IFITM10 genes from terrestrial vertebrates. Such division might distinguish aquatic-and terrestrial-type of IFITM10 and accordingly the amphibian frog possesses both types. These findings suggest that functional divergence of IFITM10 in the evolution of vertebrates may have occurred during the transition from an aquatic to a terrestrial environment. 