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Posted : 2011-08-09 15:33
Updated : 2011-08-09 15:33

Glowing shark wears ‘Cloak of invisibility’since 75 mil. years ago




The first detailed study of the rare splendid lantern shark reveals that not only does it glow in the dark, but the light effects create a "cloak of invisibility" that helps shield it from predators.

The study, accepted for publication in the Journal of Experimental Marine Biology and Ecology, is also the first to document the cylindrical-shaped shark's presence in waters around the Okinawa Islands of Japan, the Discovery News reported on Aug. 3.

Previously, the shark was only confirmed to exist in the East China Sea, off Taiwan, and in the waters around southern Japan.

Its natural light show, produced by light-emitting organs called photophores, serves many functions. The cloak of invisibility is perhaps one of the most beneficial, since it helps to protect the small, shark from upward-looking predators. The lantern shark is a member of the small dogfish sharks.

"The photophores replace the down-welling light from the sun, which is absorbed by the shark's body," lead author Julien Claes explained to Discovery News. "The silhouette of the shark therefore disappears when seen from below."

Claes, a postdoctoral researcher in the Catholic University of Louvain’s Marine Biology Lab, and colleagues Keiichi Sato and Jerome Mallefet collected, and maintained in captivity, three specimens of the splendid lantern shark.

Analysis of the sharks revealed that each had nine distinct luminous zones where light was emitted. Some of these zones, such as one on the belly, contribute to the "cloak of invisibility" effect. Other, even brighter, zones are present on the shark's sexual organs, flanks, tail and pectoral fins. The researchers suspect these are probably used during schooling and sexual communication.

"Sharks use internal fertilization, so the presence of photophores on the sexual organs may facilitate mating," Claes said. "Moreover, it might also be a way for the sharks to signal that they are ready to mate or that they are a better candidate for reproduction in a light-induced sexual selection system."

The scientists believe nerves and hormones primarily control the light, with pigments also moving in cells as part of the process.

The luminescence likely evolved when lantern sharks colonized the deep sea probably during the end of the Cretaceous, 65 to 75 million years ago. The splendid lantern shark to this day lives 656 to 3281 feet below the water's surface, an area with extremely low light levels.

Claes and his colleagues previously studied another member of this shark family, the velvet belly lantern shark. Both this and the splendid lantern shark share similar luminous zones and other features. It's therefore probable that their ability to glow evolved long before their clades split up at least 31.55 million years ago.

It's even possible that many other prehistoric marine animals could glow in the dark.

"Unfortunately bioluminescence is a soft-tissue phenomenon that leaves no, or extremely few, fossil tracks," Claes said. "It is therefore very difficult to establish if a lot of prehistoric animals were luminous, but it is probably the case at least in the deep sea, since bioluminescence is currently widespread in this environment."

Nicolas Straube, a researcher at the Bavarian State Collection of Zoology, told Discovery News that he "fully agrees" with the new paper's conclusions.

Straube explained that this latest study supports previous theories about lantern shark evolution and luminescence, given both the similarities and differences between the two best-documented species: the velvet belly lantern shark and now the splendid lantern shark.

At least 33 species exist in this diverse shark family, however, so much remains to be discovered about these dwellers of the ocean depths.
관련 한글 기사

투명 상어, 투명망토 입은 듯 사라져

자신의 몸을 갑자기 보이지 않게 만드는 일명 '투명 상어'가 발견돼 학계의 관심이 모아지고 있다.

디스커버리 뉴스에 따르면 3일(현지시간) 최근 일본 오키나와에서 투명상어가 발견됐으며 이 상어가 천적으로부터 자신을 지키기 위해 몸 일부를 투명하게 할 수 있다고 전했다.

랜턴상어(Lantern shark)로 명명된 투명상어는 피부 특수한 조직이 태양빛을 흡수한 뒤 다시 발광하는 생물방광으로 빛을 왜곡시켜 몸을 투명하게 만든다고. 천적이 나타나면 몸을 투명망토를 입는 것처럼 사라지게 만드는 것이 이 랜턴상어의 보호기능이다.

과학자들은 이 투명상어가 약 6500~7500만년전인 백악기 마지막 기간 동안부터 깊은 바다에서 살며 투명해지는 기능이 진화한 것으로 보고 있다. 특히 한국, 중국, 일본 등의 심해에서 서식하는 것으로 알려져 더욱 관심을 모은다.

과학자들은에 따르면 랜턴상어는 복부와 옆구리, 꼬리, 지느러미, 생식기관 등의 9곳에 발광포가 존재한다. 발광포라는 특수 조직이 투명망토의 역할을 하고 있다.

한편 최근 영화 '해리포터 시리즈'에 등장했던 투명망토가 현실에서 가능하다는 소식이 전해진 것에 이어 투명물고기까지 등장함에 따라 투명인간에 대한 관심도 커지고 있다.

지난 3일(현지시간) 미국 뉴스사이트 'MSNBC'는 미국 버클리대 연구팀이 '메타물질'이라는 신물질을 이용해 '투명망토' 개발에 성공했다고 전했다.

'MSNBC'에 따르면 버클리대 연구팀이 개발한 투명망토는 넓이 0.000024인치, 높이 0.000012인치로 아주 작은 물체를 숨기는데 성공했다.

지금까지는 전자기장을 활용해 물체 일부를 안보이게 하거나 특정 조건에서만 물체를 투명하게 만드는 기술이 전부였던 만큼 학계의 관심이 모아지고 있다. 버클리대 로렌스 버클리연구소 연구진은 빛의 굴절원리를 이용해 투명 메타물질을 만든 것으로 알려졌다.

투명망토의 원리는 표면에 특수 패턴이 새겨진 구멍이 있어 이 구멍들이 빛의 속도를 바꾸고 각도를 굴절시켜 사람들이 물체를 식별할 수 없게 만드는 것.

연구팀은 "이번 투명망토를 만드는데 약 1주일이 걸렸다"며 "크게 하는 것도 가능하겠지만 상당한 시간이 필요할 것"이라고 말했다.

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