highly significantp < 0.001
Despite the protein-coding region evolving under an overall conservative tendency, the likelihood ratio test comparing the likelihood scores of site models M7 (beta) and M8 (beta + ω > 1) yielded a test statistic of LRT = 40.34, which is highly significant under a chi-squared distribution with 2 degrees of freedom (critical value = 13.82, p < 0.001).