Scientists discover why two shark species emit green glow 深海鯊魚發出螢光 科學家破解背後謎團

Sun, Aug 18, 2019 - Page 9

The secret behind the eerie glow of two shark species has been revealed in a study that sheds light on the origin and possible advantages of their fluorescent green bodies.

Chain catsharks and swell sharks are deep-dwelling and live in the western Atlantic and eastern Pacific respectively, where they hide among rocks and rubble. While at first glance they appear to be in various shades of brown, recent studies have shown that under blue light they glow green. Crucially, only blue light penetrates the depths of the ocean.

Now scientists have pinpointed the chemicals behind the phenomenon, which not only cause the green glow, but possibly help defend the sharks against harmful microbes. “We have so much more to learn about life in the ocean and sharks,” said professor David Gruber, of City University of New York, a co-author of the study.

The green glow emitted by the sharks is a type of biofluorescence, which arises when blue light in the oceans is absorbed and then re-emitted, in this case as green light. Writing in the journal iScience, the team said the green glow of the sharks was limited to certain parts of their bodies — typically where the skin was paler or where there were white spots.

The team took skin tissue samples and analyzed them, finding between the two species a range of eight fluorescent molecules that glowed when blue light was shone on them. Among those predominantly found in the paler areas of the skin was one in particular, present in both species, that gave off a bright green glow.

The team’s previous research has suggested that the visual system of these sharks seems tuned in to such hues. “They just have one visual pigment in their eye,” said Gruber. “It sees right at the blue-green interface.”

Gruber said the research suggested the glow might aid communication between the sharks, noting that males and females showed different light patterns. “If these sharks are absorbing blue and then creating green [light], they are creating contrasts for each other, because there is no green [light] down there except the green that they are producing on their skin,” he added.

The study suggests that there might be additional benefits. The team tested the fluorescent substances for their action against certain bacteria: one found in marine environments and the other MRSA — the hospital superbug. Growth of both bacteria were found to be hampered by some of the substances within the sharks’ skin — a finding the team says might indicate that molecules involved in biofluorescence could also be part of microbial defense.

“These sharks lay on the bottom and the bottom has a high density of bacteria,” said Gruber, adding that substances in the skin might protect the animals. “We are just hypothesizing it could be a way to stop things from growing on the shark.”

(The Guardian)

近日一項研究揭露出兩種鯊魚身上發出詭異光芒背後的秘密,並為它們螢光綠身體的起源及可能的優勢指點明燈。

網紋貓鯊和絨毛鯊分別棲息於大西洋西部和太平洋東部的深海中,躲藏在大塊礁石和碎石間。乍看之下,這兩種鯊魚身上呈現出深淺不一的褐色,然而近年的研究卻顯示,它們會在藍光底下發出綠色的光。關鍵就是:只有藍光能夠穿透海洋的深處。

科學家日前已確認此現象背後作用的化學物質,它們不只產生綠光,還可能幫助鯊魚抵抗有害的微生物。該研究的共同作者、來自美國紐約市立大學的大衛‧格魯博教授表示:「對於海洋中的生命和鯊魚,我們有太多需要學習的地方。」

這兩種鯊魚發出的綠色光屬於一種生物螢光機制,是因為海洋中的藍色光被吸收後再次向外發散,在這個案例中則呈現出綠色。在這篇發表於期刊《iScience》的論文中,研究團隊指出,這些鯊魚的綠色光僅限於身體的特定部位──通常是皮膚顏色較淺的地方,或是身上的白斑處。

研究團隊採集了皮膚組織樣本,並進行分析,在這兩種鯊魚身上發現一系列八種螢光分子,會在藍光照射下發光。主要在皮膚顏色較淺部位發現到的分子中,特別有一種同時出現在這兩個物種身上,會發出明亮的綠色光芒。

此團隊先前的研究顯示,這兩種鯊魚的視覺系統似乎調整為固定接收這類色調。格魯博教授表示:「它們的視覺系統直接對準光譜上藍色和綠色的交界部分。」

格魯博指出,研究結果顯示,鯊魚發出的光可能有助於彼此之間的交流,同時也提到公鯊和母鯊會呈現不同的發光型態。他補充解釋:「如果這些鯊魚吸收了藍色,再製造出綠色(光),那表示它們在為彼此之間製造對比色,因為在深海中,除了它們在皮膚上製造的綠色光之外,沒有別的綠色(光)存在。」

該研究也指出發光可能帶有額外的益處。研究團隊對螢光物質進行測試,觀察它們如何抵抗特定細菌:其中一種細菌來自於海洋環境中,而另一種則是多重抗藥性金黃色葡萄球菌──也就是醫院的超級細菌。研究團隊發現,在鯊魚皮膚中,其中幾種螢光物質會阻礙這兩種細菌的生長──科學家認為,這項發現可能暗示生物螢光的相關分子或許也是抵抗微生物機制的一部分。

格魯博指出:「這些鯊魚棲息在海底,而海底的細菌密度極高。」他補充表示,皮膚中的這些物質可能會為鯊魚提供保護。「我們目前只是假設,這項機制或許會阻止髒東西在鯊魚身上生長。」

(台北時報章厚明譯)