Seven-locus molecular phylogeny of Myctophiformes (Teleostei; Scopelomorpha) highlights the utility of the order for studies of deep-sea evolution.

Fishes of the order Myctophiformes (Teleostei; Scopelomorpha) comprise over half of all deep-sea biomass, and are a critical component of marine ecosystems worldwide. Members of the family Myctophidae, within Myctophiformes, form the majority of species diversity within the order (∼250 species, 33 genera, 2 subfamilies), and are further known for their diverse bioluminescent traits, comprised of distinct cranial, postcranial, and caudal luminous systems that is perhaps the most elaborate among all vertebrates. These features make myctophids particularly compelling from both economic and scientific perspectives, yet no studies have sampled these fishes at a density appropriate for addressing any questions requiring a phylogenetic hypothesis as input. This study therefore presents a seven-locus molecular phylogeny of the order, sampling over 50% of all nominal myctophid species. This taxon sampling triples the representation of the next most comprehensive analysis, and reveals several new and well-supported hypotheses of relationships, in addition to supporting traditional hypotheses based on combined morphological data. This analysis shows that the slendertailed myctophids Gonichthys, Centrobranchus, Loweina, and Tarletonbeania are rendered non-monophyletic by a polyphyletic Myctophum; the enigmatic, monotypic genus Notolychnus valdiviae is nested within tribe Lampanyctini; the genus Diaphus is divided into at least two clades, with the suborbital (So) group recovered as monophyletic with strong support; and the genera Lampanyctus and Nannobrachium are recovered as non-monophyletic. These molecular results highlight the potential of myctophids as a premier model system for the application of modern comparative methods to studies of deep-sea evolution.