^aG+C content.

^bB_I is the level of strand bias (Methods).

^cDifference in GC skew between genes in the leading and in the lagging strand.

^dDifference in AT skew between genes in the leading and in the lagging strand.

^eMaximal d_S among the taxa and number of sites in the alignments. d_S between the outgroup and the most distant ingroup.

^fOnly ingroups analyzed.