Neighbor-joining tree based on Mc1r gene sequences (954 bp) from seven species of rats of the Tribe Rattini, with Mus musculus included as an outgroup. Numbers at nodes denote bootstrap values (> 50%) for the NJ method and a maximum parsimony (MP) analysis that yielded a tree with identical topology. The rates of nonsynonymous and synonymous changes (dN and dS) and their ratios (dN/dS), as inferred with codeml in the PAML package (Yang, 1997), are shown under and on branches, respectively. An asterisk with numerical number on the branch leading to R. exulans indicates that reached nearly significance in comparison of the two-ratio model with the one-ratio model (P = 0.08).