Fig. 3

The abundance of repeat sequences of 9 bp in the amphibian phylogenetic tree. The figure presents the 221 amphibian mitogenomes classified into three orders, with their respective abundance of direct and inverted repeat sequences shown as bar graphs. The amphibians with a higher abundance of direct repeats seem to appear as random events in the amphibian phylogenetic tree, and the same pattern is observed for the inverted repeats of the orders Anura and Gymnophiona. On the contrary, the majority of the amphibians of the order Caudata display an increase abundance of inverted repeats. The number above each bar graph represents the abundance of repeat sequences (repeats /Kbp). The images with distributions of repeat sequences of other lengths can be accessed from Additional file 3