In The Abyss: Studying The Evolution of Deep-Sea Corals
Scott France, Associate Professor of Biology, University of Louisiana at Lafayette
25 Sep 2009
The 19th century concept of an azoic deep sea – lifeless below 545 meters – has long been abandoned. With the discovery of high species diversity in the bathyal benthos, more recent questions focus on the origin of deep-sea species, the processes that lead to speciation in this comparatively monotonous environment, and biogeography. In my lab we examine these questions using deep-sea corals as a model system. We focus on “gorgonian-type” corals (Cnidaria: Octocorallia), in particular four families whose diversity and abundance reaches a maximum at depths greater than 200 meters (Chrysogorgiidae, Isididae, Paramuriceidae, Primnoidae), and black corals (Cnidaria: Hexacorallia). Our results show support for multiple evolutionary radiations of deep-sea taxa. Phylogenetic analyses (mitochondrial and nuclear genes) show strong support for a monophyletic Primnoidae, and although both the Chrysogorgiidae and Isididae are polyphyletic, it is the inclusion of shallow-water taxa in these families that appear to be the cause: the strictly deep-water genera do form robust monophyletic clades. The relationships among the deep-water clades from the different families remain unresolved due to short internal branch lengths in the phylogeny, an indication of a relatively-rapid radiation in the past. Biogeographically, there is little evidence for local endemicity on habitat islands. However, these taxa may have been a poor choice to study intraspecific patterns as corals evolve at a particularly slow rate compared to other metazoans (at least in terms of the mitochondrial genome).