Fig. 5

Evolution of major phototransduction pathways in animals. 1 Mutations (Illustrated with star graphic) to a pre-existing GPCR gene in early animals (~600 MYA) gave rise to opsin. Recent comparative evidence suggests the first opsin relied on a ciliary G protein pathway (red branches). At some time following its origin, this gene duplicated, generating at least two different opsins. 2 Prior to the divergence of bilaterian animals, mutations (illustrated with star graphic) to one of the ciliary opsins led to the co-option of a different G protein pathway. This shift can be considered the origin of rhabdomeric (blue branches) phototransduction.