Fig. 2

Amino acids under selective pressure. Upper rectangles indicate the ecto-domain 1, ecto-domain 2, and endo-domain, whereas lower rectangles indicate the signal peptide, trans-membrane 1, and trans-membrane 2 regions. The red lines and blue lines indicate sites under significant positive and negative selection, respectively. dN-dS represents the normalized dN–dS value according to the FEL method