Gene duplications and the dS distribution of paralogs and orthologs among three Nosema species. Abbreviation: Na, N. antheraeae; Nb, N. bombycis; Nc, N. ceranae. (A) A circos map showing the comparative genomics among three different Nosema species based on all available scaffolds. Each line represents the homologous syntenic regions between any two species or between any given two chromosome positions of single species. Many lines across different scaffolds of N. bombysis indicates higher rate of segmental syntenic duplications. (B) The dS distribution of segmental paralogs of Nb and the orthologs between Nb and Na showing a higher dS values in orthologs in general. Notably, a higher peak (arrow) seen in Nb suggests the possibility of a burst of paralogs recently over the Nb evolution after the separation of Na and Nb. (C) An example of syntenic comparisons among three Nosema species showing a cluster of tandem paralogs. The corresponding genetic position and names of identified element are provided in Additional file 8. The number of all identified tandem paralogs for each Nosema genome is summarized on the right side. (D) The dS distribution of tandem paralogs of Nb and orthologs between Na and Nb showing that majorities of tandem paralogs arose after the separation of Na and Nb because the dS values of those tandem paralogs are smaller than that of orthologs.