Abstract
Here we consider the role of depth as a driver of evolution in a genus of deep-sea fishes. We provide a phylogeny for the genus Coryphaenoides (Gadiformes: Macrouridae) that represents the breadth of habitat use and distributions for these species. In our consensus phylogeny species found at abyssal depths (>4000m) form a well-supported lineage, which interestingly also includes two non-abyssal species, C. striaturus and C. murrayi, diverging from the basal node of that lineage. Biogeographic analyses suggest the genus may have originated in the Southern and Pacific Oceans where contemporary species diversity is highest. The abyssal lineage seems to have arisen secondarily and likely originated in the Southern/Pacific Oceans but diversification of this lineage occurred in the Northern Atlantic Ocean. All abyssal species are found in the North Atlantic with the exception of C. yaquinae in the North Pacific and C. filicauda in the Southern Ocean. Abyssal species tend to have broad depth ranges and wide distributions, indicating that the stability of the deep oceans and the ability to live across wide depths may promote population connectivity and facilitate large ranges. We also confirm that morphologically defined subgenera do not agree with our phylogeny and that the Giant grenadier (formerly Albatrossia pectoralis) belongs to Coryphaenoides, indicating that a taxonomic revision of the genus is needed. We discuss the implications of our findings for understanding the radiation and diversification of this genus, and the likely role of adaptation to the abyss.
Highlights
The deep oceans (>200 m depth) are vast three-dimensional habitats characterized by decreasing sunlight, low temperatures, and increasing hydrostatic pressures with depth
Our phylogenetic treatment of Coryphaenoides indicates that the morphologically based analyses used to date are insufficient to resolve the relationships among species
Taxa inhabiting waters deeper than 4000 m form a distinct and well-supported lineage, which includes two non-abyssal species, C. striaturus and C. murrayi, which diverge from the basal node
Summary
The deep oceans (>200 m depth) are vast three-dimensional habitats characterized by decreasing sunlight, low temperatures, and increasing hydrostatic pressures with depth. Life in these extreme habitats is almost entirely reliant upon the organic nutrients that rain down from the photic zone (vent and seep communities are the exception; Snelgrove and Smith, 2002). These habitats were long believed to be environmentally homogenous.
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