Different speciation processes in a cryptobenthic reef fish from the Western Tropical Atlantic

The saddled blenny Malacoctenus triangulatus is a widely distributed species of cryptobenthic reef fish that occurs from the Caribbean to southeastern Brazil, including the oceanic islands. Subtle morphological differences have been observed between populations, suggesting some degree of structuring along its distribution, especially between insular and coastal environments. In this study, we conducted phylogeographic analyses of M. triangulatus based on mitochondrial (cytochrome oxidase I and cytochrome b) and nuclear (rhodopsin) genes, including sequences of M. brunoi, a closely related species endemic to the oceanic islands of southeastern Brazil. Three highly structured lineages were identified within the M. triangulatus complex: one restricted to the Caribbean province probably isolated by the Amazon barrier, and two in the Brazilian province, one in the northeastern oceanic islands (NOI) and another along the coast (including M. brunoi). This result indicates that divergent evolutionary processes have driven the evolution of the saddled benny in the Tropical Southwestern Atlantic: an ancient isolation of the NOI lineage during the Neogene and a recent ecological speciation event in the southeastern oceanic islands, which were connected to the coast during Pleistocene marine regressions. Together, these results provide insights on the evolutionary patterns and oceanographic barriers in the Western Tropical Atlantic.