highly significantP < 0.0001
This showed that the effect of gene category (i.e., the difference in dN between genes encoding PRR and cytokines on one hand and those encoding signaling proteins and transcription factors on the other) remained highly significant ( F = 42.9, df = 3, 304, P < 0.0001) even when controlling for a negative correlation between sequence divergence and pleiotropy ( F = 5.04, df = 1, 304, P = 0.026), and an interaction between gene category and expression divergence ( F = 3.41, df = 3, 304, P = 0.018; see supplementary table S1 , Supplementary Material online for full model details).