Bioluminescence Is Spreading to New Fish Species

The deep-sea hatchetfish, which gets its name from the distinct hatchet-like shape of its body, has light-producing organs known as photophores that run along the length of its body and point downward. Hatchetfishes use these structurally complex photophores to mimic any down-welling sunlight and disappear from predators lurking below. . Sparks, R. Schelly, D. Roje

One of the best parts of summer on the East Coast or in the Midwestern United States is spending your nights gazing up at a dark sky, an open jar in one hand and a lid in the other, searching for little balls of light to pounce at and capture. Fireflies radiate a fuzzy glow thanks to bioluminescence, a chemical reaction that takes place in living organisms, producing and emitting visible light. Though fireflies are probably the most familiar bioluminescent creature, the phenomenon is fairly common among bacteria and fungi, as well as in the deep depths of the ocean, where almost all organisms glow and use it for communication, feeding and reproduction.

New research shows that this marvel of light has developed in many more animals than previously thought. In a study published on June 8 in the journal PLOS One, scientists from the American Museum of Natural History, St. Cloud State University and the University of Kansas count at least 27 different marine saltwater fish lineages that have evolved to bioluminesce. That, the study's authors say, signifies a likely even greater number of bioluminescent species across all sorts of animal types. "If we are seeing these kind of numbers in marine fishes alone, bioluminescence has evolved far more than 40 times across the tree of life," estimates John Sparks, the curator-in-charge of the Museum's Department of Ichthyology and paper co-author.

05_09_Barbeled dragonfish
This barbeled dragonfish is a small bioluminescent deep-sea fish with a long protrusion attached to its chin, known as a barbel, which is tipped with a light-producing organ called a photophore. It also has large photophores below its eyes used to illuminate prey and potentially communicate, as well as some along the sides of its body for camouflage. J. Sparks, R. Schelly, D. Roje

This study was also the first to investigate exactly how bioluminescence has evolved in vertebrates through phylogenetic analysis, a means of estimating evolutionary relationships. Sparks, along with his colleagues W. Leo Smith from the University of Kansas and Matthew Davis from St. Cloud University, found that lineages of fish with the ability to produce light have evolved the genes that help create a light-producing reaction, which allows bioluminescence to happen. These genes are often passed on to their offspring, and since bioluminescence in fish has been around for 150 million years, it's likely it has expanded into many new species—meaning there are many more fireflies of the ocean out there, though it may take more than an old pickle jar to catch them.