Seven Species in One? DNA Barcoding Reveals High Cryptic Diversity in Ceratoscopelus warmingii (Myctophiformes, Myctophidae) a Circumglobal Mesopelagic Species

In the marine environment, pelagic ecosystems are vast and complex, with their biodiversity still being underestimated. In these regions, specifically in mesopelagic zones, the dominance of filter-feeding fish is remarkable, as is the case with Ceratoscopelus warmingii , a taxon that is globally distributed. Despite its recorded occurrence in the Atlantic, Indian, and Pacific Oceans, there is limited understanding of its genetic aspects and evolutionary cohesion across its distribution. In this study, we investigated the genetic diversity in C. warmingii on a global and temporal scale, using phylogenetic and phylogeographic approaches based on the mitochondrial marker cytochrome oxidase I. Georeferenced genetic information was obtained from the BOLD Systems Platform. Our analyses revealed the presence of seven highly structured clusters with genetic divergences exceeding 7%, widely distributed across various marine provinces. The cladogenetic events that gave rise to these clusters date back from the Miocene to the Pleistocene.These findings suggest the possibility that C. warmingii may constitute a species complex, indicating the need for extensive taxonomic revision. This study sheds light on the fundamental importance of comprehensive genetic investigation regarding underestimated species, thus contributing to a better understanding of global marine biodiversity. The implications of these results underscore the need for more careful attention to these often-overlooked ecosystems.