Global phylogeography suggests extensive eucosmopolitanism in Mesopelagic Fishes (Maurolicus: Sternoptychidae)

Fishes in the mesopelagic zone (200–1000 m) have recently been highlighted for potential exploitation. Here we assess global phylogeography in Maurolicus, the Pearlsides, an ecologically important group. We obtained new sequences from mitochondrial COI and nuclear ITS-2 from multiple locations worldwide, representing 10 described species plus an unknown central South Pacific taxon. Phylogenetic analyses identified five geographically distinct groupings, three of which comprise multiple described species. Species delimitation analyses suggest these may represent four species. Maurolicus muelleri and M. australis are potentially a single species, although as no shared haplotypes are found between the two disjunct groups, we suggest maintenance of these as two species. Maurolicus australis is a predominantly southern hemisphere species found in the Pacific, Indian and southern South Atlantic Oceans, comprising five previously allopatric species. M. muelleri (previously two species) is distributed in the North Atlantic and Mediterranean Sea. Maurolicus weitzmani (previously two species) inhabits the eastern equatorial Atlantic, Gulf of Mexico and western North and South Atlantic. Maurolicus mucronatus is restricted to the Red Sea. No Maurolicus have previously been reported in the central South Pacific but we have identified a distinct lineage from this region, which forms a sister group to Maurolicus from the Red Sea