Photon hunting in the twilight zone: Visual features of bioluminescent sharks

Aug 06, 2014
The eye of a velvet belly lanternshark. Credit: Dr. J. Mallefet (FNRS/UCL)

The eyes of deep-sea bioluminescent sharks have a higher rod density when compared to non-bioluminescent sharks, according to a study published August 6, 2014 in the open-access journal PLOS ONE by Julien M. Claes, postdoctoral researcher from the FNRS at Université catholique de Louvain (Belgium), and colleagues. This adaptation is one of many these sharks use to produce and perceive bioluminescent light in order to communicate, find prey, and camouflage themselves against predators.

The mesopelagic twilight zone, or about 200-1000 meters deep in the sea, is a vast, dim habitat, where, with increasing depth, sunlight is progressively replaced by point-like bioluminescent emissions. To better understand strategies used by bioluminescent predators inhabiting this region that help optimize photon capture, the authors of this study analyzed the eye shape, structure, and retinal cell mapping in the visual systems of five deep-sea bioluminescent sharks, including four Lanternsharks (Etmopteridae) and one kitefin shark (Dalatiidae).

The researchers found that the sharks' eyes contained a translucent area present in the upper eye orbit of the , which might aid in adjusting counter-illumination, or in using bioluminescence to camouflage the fish. They also found several ocular specializations, such as a gap between the lens and iris that allows extra light to the retina, which was previously unknown in sharks. Comparisons with previous data on non-bioluminescent sharks reveals that bioluminescent sharks possess higher rod densities in their eyes, which might provide them with improved temporal resolution, particularly useful for bioluminescent communication during social interactions.

"Every bioluminescent signal needs to reach a target photoreceptor to be ecologically efficient. Here, we clearly found evidence that the visual system of bioluminescent sharks has co-evolved with their light-producing capability, even though more work is needed to understand the full story," said Dr. Claes.

These results reveal an unexpected diversity of photon capture strategies and indicate that like other deep-sea animals, deep-sea possess a number of adaptations to cope with the twilight zone.

Explore further: Great white sharks plentiful off US west coast

More information: Claes JM, Partridge JC, Hart NS, Garza-Gisholt E, Ho H-C, et al. (2014) Photon Hunting in the Twilight Zone: Visual Features of Mesopelagic Bioluminescent Sharks. PLoS ONE 9(8): e104213. DOI: 10.1371/journal.pone.0104213

Related Stories

Smalleye pigmy sharks' bellies shine

Apr 26, 2012

Smalleye pigmy sharks have an eye-catching party trick: Their bellies glow. However, instead of being a giveaway, Julien Claes and Jérôme Mallefet from Université catholique de Louvain, Belgium, have shown ...

Great white sharks plentiful off US west coast

Jun 16, 2014

Great white sharks are likely rising in numbers off the coast of California and are not at risk of extinction despite some reports to the contrary, US researchers said Monday.

Humane strategy reduces shark attacks

Aug 04, 2014

A simple and humane technique may be an effective strategy to reduce human encounters with sharks without harming populations of threatened shark species.

Recommended for you

Do you have the time? Flies sure do

1 hour ago

Flies might be smarter than you think. According to research reported in the Cell Press journal Current Biology on May 28, fruit flies know what time of day it is. What's more, the insects can learn to con ...

Barking characterizes dogs as voice characterizes people

4 hours ago

An international group of researchers has conducted a study on canine behavior showing that gender, age, context and individual recognition can be identified with a high percentage of success through statistical ...

Bird beaks feeling the heat of climate change, say scientists

5 hours ago

While the human population grapples with ways to counter the effects of climate change, Deakin University research has discovered that birds might have been working on their own solution for the past 145 years – grow bigger ...

How longhorned beetles find Mr. Right

17 hours ago

A longhorned beetle's sexy scent might make a female perk up her antennae. But when the males of several species all smell the same, a female cannot choose by cologne alone.

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.