deep sea

The visual system of most deep sea organisms is able to detect short-wave blue wavelengths. Loosejaw dragonfish are able to detect longer wavelengths of light and emit these wavelengths as the color red through bioluminescence. The authors sought to understand the timing of the evolution, the number of times the trait evolved, and whether it arose due to positive selection. The findings for the evolution of the red visual system were more complex than expected. The red visual system was found to have evolved once as a single evolutionary event within loosejaws. They found that at approximately 15.4 Ma, far red visual systems evolved and at 11.2 Ma the primitive blue visual system re-appeared in the most recent common ancestor of dragonfish. The authors also investigate the phylogenetic relationships between Stomiidae and found that the relationship between this family and loosejaws is paraphyletic. The significance of this study in the context of spectral tuning in deep sea organisms is that it provides a phylogenetic approach to analyzing the evolution of the red visual system.