Bioluminescence in Deep-Sea Fishes Breeds Species Diversity

Bioluminescence is used by deep-sea fishes to promote communications and mating in the open ocean, according to new research.

Writing in the journal Marine Biology, a research team including scientists from the American Museum of Natural History report that, for the first time, it has been observed that deep-sea fishes that possess bioluminescence structures that are unique to their species are leading to a more rapid diversification of new species.

Deep-sea fishes such as lanternfish and dragonfish possess bioluminescence, which is the  production and emission of light from a living organism through a chemical reaction. Bioluminescence is thought to occur in the majority of life that inhabits the deep sea.

"Bioluminescence is quite common in the deep sea, and many fishes inhabiting this region exhibit complex, species-specific patterns of light-producing structures," said John Sparks, a curator in the American Museum of Natural History's Department of Ichthyology and one of the co-authors on the study. "But we still have so much to learn about how these animals use bioluminescence-for predation, camouflage, communication, or something else. This new work provides insight into how this phenomenon might have shaped present-day biodiversity in the deep open ocean."

In the deep sea, fishes that utilize bioluminescene in acts of camouflage or predation are diversifying into new species at a more rapid rate than deep-sea fishes that do not, the researchers found.

The deep ocean lacks many of the physical barriers that promote species isolation. On land, for instance, mountain ranges and rivers can genetically isolate species from one another. But in the deep sea, gene flow is not restricted by such barriers.

"This has traditionally been considered one of the reasons why there is a comparatively low level of fish species richness in the deep sea," the AMNH said in a statement. "For example, bristlemouths, which are among the most abundant vertebrates on Earth, are represented by only 21 species. But that's not the case for all fishes. Lanternfishes, which inhabit the same mid-water, or mesopelagic, area of the ocean, have diversified into more than 250 species."

Matthew Davis, a research associate at the University of Kansas and the study's lead author, said the comparison of lanternfishes and bristlemouths makes for an ideal scenario for studying speciation in the deep seas.

"Both bioluminescent groups are among the most abundant vertebrates on Earth and live in the same dark environment," Davis said. "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."

Leo Smith, an assistant curator of ichthyology at the University of Kansas and a co-author on the paper, said that the team was able to exhibit that deep-sea fishes that have unique bioluminescent organs have increased rates of diversification.

"This suggests to us that bioluminescent signaling may be critical to diversification of fishes in the deep sea," he said.