Amphibians have immunoglobulins similar to ancestral IgD and IgA from Amniotes

•Long IgD are found in amphibians are similar to the ancestral IgD of Amniotes.•Some amphibians have more than one genes for IgD.•There exists two isotypes IgA/X in amphibians.•One isotype corresponds to IgA in mammals; gene located beyond the IgY gene.•Other isotype corresponds to IgA in crocodiles and birds; gene located between IgD and IgY. We studied the immunoglobulin genes from either the genomes or RNAs of amphibians. In particular, we obtained data from one frog genome (Nanorana parkeri) and three transcriptomes of the Caudata order (Andrias davidianus, Notophthalmus viridescens and Cynops pyrrhogaster). Apart from the immunoglobulins IgM and IgY previously described, we identified several IgD related immunoglobulins. The species N. parkeri, N. viridescens and C. pyrrhogaster have two IgD genes, while Andrias davidianus has three such genes. The three Caudata species have long IgD immunoglobulins similar to IgD of reptiles, and could be an ancient relic from the common ancestor of IgD of all mammals and reptiles. We also found two IgA isotypes. The results suggest that one of the IgA may be the ancestor of IgA in crocodiles and birds, while the other could be the ancestor IgA found in mammals. These results provide information that could help understand the evolution of immunoglobulins in terrestrial vertebrates.