DNA reconciles morphology and colouration in the drunk blenny genus Scartichthys (Teleostei: Blenniidae) and provides insights into their evolutionary history

The blenniids of the genus Scartichthys represent key herbivore species of central and south American Pacific coastal reefs. Yet Scartichthys spp. remain difficult to identify in the field, especially across the c.a 6000 km where three of the four currently accepted species are known to occur in sympatry. The main diagnostic characters from traditional taxonomy that have been used to revise this genus are indeed elusive. At the same time, species can display multiple colour patterns in the field, depending on the ontogenetic stage, habitat association, and/or reproductive behaviour. Overall, molecular characterization is warranted to help address these issues. Here, we used a combination of colouration, morphological and molecular data for the first time, including specimens representative of the four currently valid species and seven described colour patterns. Our integrative approach revealed that only three of the four species should be considered as valid; Scartichthys gigas (Steindachner, 1876), S. variolatus (Valenciennes, 1836) and S. viridis (Valenciennes, 1836); while S. crapulatus Williams 1990 should be synonymized with S. viridis. In the same way, our analyses show that one of the colour patterns attributed so far to S. gigas is characteristic of the juvenile stages of S. viridis. Our time-calibrated phylogeny shows that this genus is relatively young, with an estimated time of divergence between Scartichthys gigas and S. viridis of around 1.71 Ma. In comparison, the Desventuradas and Juan Fernandez Islands endemic S. variolatus diverged about 1.95 Ma. Our results help to clarify the taxonomy of the Scartichthys genus.