Fig. 6.

Ecdysozoan- and Nematode-specific genes are more conserved in their expression between C. elegans and A. nanus. (A) Genes were grouped according to their phylostratigraphic age (Left, see SI Experimental Procedures). Expression divergence index (ED) of C. elegans and A. nanus orthologs in comparison with their phylostratigraphic age. Phylostratigraphic age was calculated by blasting against a previously reported database (47) using the Phylostratigraphy software (https://github.com/AlexGa/Phylostratigraphy.git). A statistical test of difference in ED distributions for phylostratigraphic nodes revealed significance of divergence for comparisons in Nematoda, but not for genes that evolved before the phylum. The ED appears to follow an hourglass shape through evolutionary time, with evolutionary very old and young genes showing less constrained ED than those acquired on intermediate nodes in Nematoda. (B) Average expression profiles of genes of a common phylostratigraphic age for the three indicated species. Black dots indicate the stage for each category at which average expression is at its maximum.