NEWSLETTER 03/2014 18.03.2014

Unlike on land, where rivers, mountain ranges, and other physical obstacles can genetically isolate animals from one another resulting in speciation events over time, in the deep open ocean there are few obvious physical barriers to reproduction and gene flow. This has traditionally been considered one of the reasons why there is a comparatively low level of fish species richness in the deep sea. 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.

"The comparison of lanternfishes and bristlemouths is ideal for studying speciation in the deep sea. Both bioluminescent groups are among the most abundant vertebrates on Earth and live in the same dark environment," said 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. This is not the case for photophores on the belly. 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 American Museum of Natural History's Irma and Paul Milstein Family Hall of Ocean Life through March 5, 2014.

Story Source:

The above story is based on materials provided by American Museum of Natural History. Note: Materials may be edited for content and length.

Journal Reference:

1. Matthew P. Davis, Nancy I. Holcroft, Edward O. Wiley, John S. Sparks, W. Leo Smith. Species-specific bioluminescence facilitates speciation in the deep sea. Marine Biology, 2014; DOI: 10.1007/s00227-014-2406-x

For the first time, researchers at the University of Hawaii and the University of Tokyo outfitted sharks with sophisticated sensors and video recorders to measure and see where they are going, how they are getting there, and what they are doing once they reach their destinations.

Scientists are also piloting a project using instruments ingested by sharks and other top ocean predators, like tuna, to gain new awareness into these animals' feeding habits. The instruments, which use electrical measurements to track ingestion and digestion of prey, can help researchers understand where, when and how much sharks and other predators are eating, and what they are feasting on.

The instruments are providing scientists with a "shark's eye" view of the ocean and greater understanding than ever before of the lives of these fish in their natural environment.

"What we are doing is really trying to fill out the detail of what their role is in the ocean," said Carl Meyer, an assistant researcher at the Hawaii Institute of Marine Biology at the University of Hawaii at Manoa. "It is all about getting a much deeper understanding of sharks' ecological role in the ocean, which is important to the health of the ocean and, by extension, to our own well-being."

Using the sensors and video recorders, the researchers captured unprecedented images of sharks of different species swimming in schools, interacting with other fish and moving in repetitive loops across the sea bed. They also found that sharks used powered swimming more often than a gliding motion to move through the ocean, contrary to what scientists had previously thought, and that deep-sea sharks swim in slow motion compared to shallow water species.

"These instrument packages are like flight data recorders for sharks," Meyer said. "They allow us to quantify a variety of different things that we haven't been able to quantify before."

"It has really drawn back the veil on what these animals do and answered some longstanding questions," he added.

Meyer and Kim Holland, a researcher also at the Hawaii Institute of Marine Biology, are presenting the new research today at the 2014 Ocean Sciences Meeting co-sponsored by the Association for the Sciences of Limnology and Oceanography, The Oceanography Society and the American Geophysical Union.

Sharks are at the top of the ocean food chain, Meyer noted, making them an important part of the marine ecosystem, and knowing more about these fish helps scientists better understand the flow of energy through the ocean. Until now, sharks have mainly been observed in captivity, and have been tracked only to see where they traveled.

These new observations could help shape conservation and resource management efforts, and inform public safety measures, Holland said. The instruments being used by scientists to study feeding habits could also have commercial uses, including for aquaculture, he added.

Story Source:

The above story is based on materials provided by American Geophysical Union.Note: Materials may be edited for content and length.