Fig. 5

Levels of T. hominis gene expression are correlated with gene history and conservation among microsporidians. T. hominis genes can be classified according to the period in evolutionary history when they first arose: core eukaryotic genes, shared with most or all other eukaryotes and encoding fundamental features of eukaryotic cell biology; ancestral microsporidian innovations, found only in T. hominis and other microsporidians; and recent innovations, genes found only in T. hominis and its close relative V. culicis. This density plot shows the distribution of expression levels (as log₁₀FPKM) for T. hominis genes in each of these three categories. Mixed-effects modelling indicates that core eukaryotic genes and ancestral microsporidian innovations are expressed at significantly higher levels than recently-evolved T. hominis genes (P = 0), but that there is no significant difference in expression patterns between the former two classes (P = 0.166); the recently-evolved genes also show a much broader range of expression than the older gene classes, perhaps reflecting greater variation in functional constraints within this group