Depth-adapted Gene Discovery in Deep-sea Corals

Deep-sea corals, at depths greater than 200m, are subjected to harsh environmental conditions such a high pressure, extreme temperature, and limited food sources. However, still little is known about the evolutionary processes in corals in these environments. The mitochondrial genome, which codes for genes associated with cellular-energy functions, may provide insight into how deep-sea stressors influence the adaptive evolution of corals to withstand harsher conditions. In this study, we performed a positive selection analysis on the mitochondrial protein-coding genes (PCGs) between deep- and shallow-water species of octocorals and scleractinians. We found that the ratio of nonsynonymous to synonymous mutations, ω (dN/dS), in octocorals and scleractinians for all PCGs was less than one and thus under strong purifying selection. The same data set showed that deep-sea octocorals experienced a significantly higher ω ratio than shallow-water corals within the genes: cox1, cox3, cytb, mtMutS, nad1, and nad4 This shows that deep-sea species of octocorals experience relaxed purifying selection compared to their shallow-water counterparts. Further analysis showed evidence for two positively selected sites within the nad1 gene of deep-sea octocorals. Through a phylogenetic framework, this study provides new insights regarding the adaptation of deep-sea corals for their success within this extreme environment.

Image credit: NOAA Office of Ocean Exploration and Research