Table 2. Summary of d_N/d_S analysis for the srz family.

Group	No. of genes	Tree length	Added dN/dS	No. of sites	P value	-2ΔML
C. briggsae
A	8	14.0	5.3*	13	<0.0001	70.0
B	11	23.8	3.5*	8	<0.0001	49.4
C	6	36.6	2.9	8	∼0.0001	18.2
D	5	8.9	11.5*	10	<0.0001	49.4
E	9	37.4	34.1*	11	<0.0001	42.2
F (all)	26	82.1	3.1*	6	<0.0001	47.4
C. elegans
A	9	8.3	3.7*	17	<0.0001	95.0
B	6	6.5	2.0*	3	∼0.001	18.2
C	9	17.3	1.7	9	<0.0001	28.6
D	6	9.2	1.3	26	<0.0001	23.2
E	6	15.7	2.9*	4	<0.0001	27.4
F	5	14.0	1.4	4	∼0.001	10.2
G	10	32.1	1.3	3	∼0.001	11.2
H (all)	51	102.7	2.0*	13	<0.0001	99.0

“Group” refers to the diagrams in Fig. 3. “Added d_N/d_S” is the free 11th ratio computed by model 8 in codeml. “No. of sites” is the number of sites found to be under positive selection (P ≥ 0.95). “P value” derives from the likelihood ratio test of positive selection for the group (see Materials and Methods).

^*Result was also significant (P < 0.0001) when compared to model 8 run with the 11th d_N/d_S class fixed at 1.0.