Niche divergence by deep-sea octocorals in the genus Callogorgia across the continental slope of the Gulf of Mexico

Environmental variables that are correlated with depth have been suggested to be among the major forces underlying speciation in the deep sea. This study incorporated phylogenetics and ecological niche models (ENM) to examine whether congeneric species of Callogorgia (Octocorallia: Primnoidae) occupy different ecological niches across the continental slope of the Gulf of Mexico (GoM), and whether this niche divergence could be important in the evolution of these closely related species. Callogorgia americana americana, C. americana delta, and C. gracilis were documented at 13 sites in the GoM (250-1000 m) from specimen collections and extensive video observations. On a first order, these species were separated by depth, with C. gracilis occurring at the shallowest sites, C. a. americana at mid-depths, and C. a. delta at the deepest sites. Callogorgia a. delta was associated with areas of increased seep activity whereas C. gracilis and C. a. americana were associated with narrow, yet war...