Fig. 4

Tentative reconstruction of the evolution of new OBP secretion sites. Information on expression sites of extant obp genes is inferred from the present study (dog obp) and previous proteomic studies of nasal mucosa (N), saliva (S), skin (Sk), tears (T) and vaginal secretion (V; Additional file 7). The depicted tree is based on the previously inferred gene tree pruned to include only genes for which expression information are available and modified to fit placental mammal divergence times retrieved from Ref. [84]. Nodes representing gene duplication events are labelled with ‘d’. For each expression site, the history is traced back (coloured branches) to a single origin (a labelled vertical bar). Origins were mapped on the tree by ancestral state reconstruction using the parsimony principle (see “Methods”). Uncertainty in the origin of OBP secretion in anal sac glands is indicated by a dashed line. The time window in which anal sac glands most likely originated is shown as a yellow window