Fig. 2

Orphan genes are under strong negative selection. a Distribution of gene clusters based on the number of orthologs between P. pacificus and P. exspectatus. b The graph shows the cumulative proportion of orphan and conserved gene clusters with evidence for negative selection relative to different ω thresholds in the P. pacificus – P. exspectatus orthologous clusters dataset. Using an abitrary cutoff of ω < 0.6, 78 % of all orphan clusters (N = 3571) show evidence of negative selection. c Comparison of the proportion of negatively selected orphan gene clusters and conserved gene clusters (Y-axis) based on the analysis of paralogous gene clusters. Given, that only 11 % of conserved clusters and 15 % of all orphan clusters contain P. pacificus paralogs, this analysis shows that even in the absence of other genomic data, negative selection can be investigated in a subset of orphan genes. d Cumulative proportion of orphan and conserved gene clusters under given ω value in Clade A1 – Clade A2 ortholog dataset