To detect whether positive selection acted on IFITM family, the CODEML program implemented in PAML 4.2 package was used. The site-specific model was performed by comparing the models M2a (positive selection) and M8 (beta & v) vs. the null models M1a (nearly neutral) and M7 (beta), respectively. Likelihood ratio tests (LRT) of different models were used to find the best fit model for the data [65, 66, 69] . We also used the MEME method and the branch-site REL model implemented in DATAMONKEY (http://www.datamonkey.org/) to confirm the results by PAML analyses [70, 71] . MEME is the latest method to identify PSS and can find signatures of episodic selection even when the majority of lineages are subject to purifying selection.