Matthew Davis, a research associate at the University of Kansas and the study’s lead author. “The difference in species numbers between these two groups is striking. Both use bioluminescence for camouflage, but lanternfishes have evolved a suite of light organs that act as a beacon for communication, which our work suggests have had an incredible impact on their diversification in the deep sea.”
To investigate, Sparks, Davis, and other scientists from the University of Kansas and Johnson County Community College reconstructed a tree of life for ray-finned fishes with a particular focus on the evolution of bioluminescence.
Many fishes emit light from organs called photophores that appear as luminous spots on the body. On lanternfishes, photophores are present ventrally along the belly, laterally on the flank and head, and on the tail. The researchers discovered that the common ancestor of lanternfishes most likely evolved this complex photophore system during the Late Cretaceous, between 73−104 million years ago.
The significance of the photophores on the underside of mesopelagic fishes has long been thought to provide camouflage against predators swimming below, helping them to blend in with any residual light shining down from the surface. But the function of photophores on the side of the body has been obscure, until now. Using mathematical techniques based on the anatomy of the fishes, the researchers determined that the lateral photophore patterns on certain lanternfish lineages are distinct enough to allow identification of individual species.
Recent work has shown that lanternfishes are capable of seeing blue-green bioluminescence from up to about 100 feet away, supporting the idea that lateral photophores could be used for interspecific communication.
“In this study we have shown that deep-sea fishes that exhibit unique, species-specific bioluminescent organs, like lanternfishes and dragonfishes, also exhibit increased rates of diversification,” said Leo Smith, an assistant curator of ichthyology at the University of Kansas and a co-author on the paper. “This suggests to us that bioluminescent signaling may be critical to diversification of fishes in the deep sea.”
To further test this hypothesis, the researchers plan to record lanternfish flashing patterns using emerging technology, such as remotely operated vehicles outfitted with ultra low-light underwater cameras. Other tools that might assist in this type of research include the Exosuit, a next-generation, human-piloted atmospheric diving system now on display in the Museum’s Milstein Hall of Ocean Life through this Wednesday, March 5, 2014.
Learn more about bioluminescence and researcher John Sparks's undersea explorations at SciCafe: Into the Abyss on Wednesday, March 5, starting at 7 pm. The event is free with a cash bar for ages 21+.
Learn more about the study in a press release.