Phylogenetic relationships of anuran MHC class Ia and Ib genes. The neighbor-joining tree was constructed with MEGA5 using all available anuran MHC class I genes with a sufficient length. Bootstrap values are indicated above the branches. Sample names are not shown due to the large size of the tree. Rather, the families to which these samples belong are denoted with different colors. The blue horizontal line separates MHC class Ia genes (above the line) and MHC class Ib genes (below the line). Alleles in this tree include the following: the 27 alleles isolated in the present study (family Rhacophoridae); MHC class Ia alleles from the family Hylidae (19 alleles from A. callidryas: JQ679312-JQ679330; 11 alleles from S. phaeota: JQ679380-JQ679390, ); from family Centrolenidae (12 alleles from E. prosoblepon: JQ679331-JQ679342, ); from family Ranidae (12 alleles from R. catesbeiana: JQ679343-JQ679354; 16 alleles from R. clamitans: JQ679355-JQ679370; 9 alleles from R. yavapaiensis: JQ679371-JQ679379, ; 2 alleles from R. pipiens: AF185587-AF185588, ); from family Pipidae ( 5 alleles from X. tropicalis: BC167634, BC161748, BC154904, ; NM_001112910, NM_001113065, ); 2 alleles from X. laevis: (NM_001085732, ; NM_001086402, ); and MHC class Ib alleles from family Pipidae (6 alleles from X. laevis: L20726, L20730, L20732, ; FJ589642- FJ589643, ; NM_001135072, ; 2 MHC Ib alleles from X. tropicalis: NM_001037273, NM_001247995, ).