Fig. 1

Schematic species tree showing glue gene distribution and the most parsimonious scenario for gene gains and losses. Gains are indicated by “+” and losses by “-”. Numbers correspond to the glue gene name (eg. “3” for Sgs3). An inferred distribution of glue genes in the last common ancestor is shown at the bottom. The tree is from Thomas, G.W.C. and Hahn M.W. (2017) https://doi.org/10.6084/m9.figshare.5450602. Pink is for Sgs1, yellow is for Sgs3, dark blue is for Sgs7, light blue is for Sgs8, green is for Sgs4, orange is for Sgs5-5bis, purple is for Eig71Ee. Along with each species is a schematic representation of the organization of the glue gene cluster, with relative position and orientation for the species with confirmed synteny information. Gene sizes and distances are not to scale. “R” means that internal repeats are present. “R?” means that no clear repeats were identified. In D. pseudoobscura, the relative orientation of the three clustered Sgs3-like sequences GA25425, GA23426, GA23878 suggested that GA23426 could be orthologous to Sgs3 (it is inside an intron of GA11155, homologue of Mob2, which is close to Sgs3 in D. melanogaster), GA23425 to Sgs7 and GA23878 to Sgs8. The last two had more similar sequences compared to GA23426, including the repeat region. Furthermore, the latter was neighbor to GA20420, a homologue of chrb-PC, a gene adjacent to Sgs8 in D. melanogaster