Adaptive evolution of GPR39 in diverse directions in vertebrates

•GPR39 underwent positive selection in different branches of vertebrates.•Human, frog and chicken GPR39 constitutively activate Gq and G12 signaling pathways.•Zebrafish GPR39 constitutively activates Gs, Gq and G12 signaling pathway.•Zebrafish-H2967.35 site is crucial for the activity of Gs signaling pathway.•Positive selection sites of GPR39 regulate constitutive activity of the receptor.