動物會曬傷嗎？

?，敗げ假囁?

For lots of animals—humans included—lazing about in the sunshine is one of lifes greatest pleasures. But unfortunately， this pastime comes with a cost： the skin-sizzling ordeal known as sunburn. And， while its most likely victims are the fairer-skinned among us， animals are at risk of sunburn， too.

But if this can happen to animals too， why， then， dont we ever see sunburned fish， or scarlet elephants？

“If you think of it， the sun has been here forever in terms of our planet， and all individuals have been exposed to it，” said Karina Acevedo-Whitehouse， a molecular epidemiologist from the Autonomous University of Queretaro， in Mexico. “So， its a pretty strong selective pressure that the sun has imposed on animals and that has led to many mechanisms of counteracting it.”

Some of these mechanisms are obvious： Hair， fur， wool， feathers and scales on many creatures create a barrier between sunshine and skin. These adaptations are so effective that the only time they really fail is when humans intervene. For instance， domesticated pigs—bred to have less hair—are more sensitive to sun damage than their wild cousins.

Animals with naturally hairless， unscaled skin must resort to other methods of self-protection. Elephants and rhinos not only have thicker hides; they also regularly coat themselves in dust or mud to create a rudimentary sunscreen. When conditions are extreme， most animals retreat to the shade or take refuge in burrows. “All of that is helping animals to cope， so we dont see a lot of sunburn [in these species]，” said Acevedo-Whitehouse.

Some species up the ante by producing a unique brand of sunscreen from their own cells. Taifo Mahmud， a molecular biologist at Oregon State University， has discovered genetic traits in fish， birds， reptiles and amphibians that enable them to produce a compound called gadusol， which creates protection against ultraviolet （UV） rays in the sun. “Most vertebrates， except mammals， have the genes responsible for producing gadusol，” said Mahmud. So far， theyve proved that only zebrafish actually use this compound as a protectant against UV rays. But now scientists are looking into how humans might exploit this trait for our skin.

Why dont we—and other mammals—produce gadusol？ “It has been proposed that early mammals were nocturnal. Was that because they lost the genes that produce gadusol？ We dont know，” Mahmud said. “I think it would be interesting to figure out if fur and thicker skin were developed later in their evolution.”

Not to be outdone， gadusol-deprived mammals have developed their own sophisticated mechanisms of protection. Hippos are known to secrete a scarlet liquid from their pores that looks just like blood—and it wasnt until 2004 that a group of Japanese scientists discovered that the orangey-red compounds in this skin-coating fluid protected hippos from UV rays， according to a report in the journal Nature. Other animals focus their sun protection in the most vulnerable parts of their bodies. Giraffes， for example， produce more protective melanin in their tongues—giving them a darker hue—because they spend most of their lives with their tongues exposed to the sun as they pry tender leaves off trees.

So， do animals ever get sunburned？ Yes. “Marine mammals， and specifically cetaceans [whales， dolphins and porpoises]， are an exception because they dont have fur; they dont have scales，” said Acevedo-Whitehouse， who has been studying sunburn in whales for over five years.

In skin samples taken from the backs of blue， sperm and fin whales on their cross-ocean migrations， Acevedo-Whitehouse and her colleagues discovered signs of sunburn from the whales hours spent breathing and socializing at the surface. But crucially， they also discovered that whales have specialized mechanisms that help them counteract this burn. “The common adaptation of cetaceans is that they appear to be very effective at repairing damage，” she said.

Some whales generate pigments that darken and protect their skin; others have genes that trigger a protective stress response in the skin. There are even whales that have developed a hard， keratinized layer that protects the delicate skin below. “We were excited to see there isnt really evidence of skin cancer in whales，” Acevedo-Whitehouse said. Now， theyre trying to understand precisely how those healing mechanisms work.

From protective coats， to self-made sunscreen， to rapid healing， these sun-smart animals may one day give us the clues we need to save our own skin.

對于包括人類在內(nèi)的很多動物而言，懶散地享受日光浴是生活中的一大樂事。可惜，這種消遣是要付出代價的，代價就是皮膚會遭受燒灼之苦，我們稱之為曬傷。雖然最易被曬傷的是皮膚相對白皙的人，動物也難逃被曬傷的風(fēng)險。

可是，如果動物也會被曬傷，為什么我們從來沒見過曬傷的魚或曬得紅通通的大象呢？

“想想看，對地球來說，太陽始終存在，所有物種一直在接受陽光的照射。”墨西哥克雷塔羅自治大學(xué)分子流行病學(xué)家卡琳娜·阿塞韋多-懷特豪斯說道，“因此太陽就對動物施加了較強(qiáng)的選擇壓力，使動物進(jìn)化出了許多應(yīng)對機(jī)制?！?/p>

部分此類機(jī)制顯而易見：眾多生物身上的毛發(fā)、毛皮、絨毛、羽毛、鱗甲等，在陽光和皮膚間形成了一道屏障。這類適應(yīng)機(jī)制非常有效，實際上，除了遭受人類干預(yù)外，它們從未失效過。例如，馴養(yǎng)的豬毛發(fā)減少，與其野生近親相比，對曬傷更加敏感。

天生無毛、無鱗甲的動物，必須通過其他方法保護(hù)自己。大象和犀牛不但皮更厚，它們的身上還經(jīng)常裹著一層塵土或泥漿，形成一種粗陋的防曬霜。日照極為強(qiáng)烈時，多數(shù)動物會躲避到陰涼處，或藏匿在洞穴里。“這些手段全都有助于動物抵御烈日暴曬，所以我們很少見到（這些物種）曬傷。” 阿塞韋多-懷特豪斯說。

一些物種則更進(jìn)一步，它們的細(xì)胞會產(chǎn)生一種獨特的防曬霜。俄勒岡州立大學(xué)分子生物學(xué)家泰?！ゑR哈茂德發(fā)現(xiàn)，魚類、鳥類、爬行動物和兩棲動物體內(nèi)存在一些基因特征，使這些動物能夠分泌出一種叫作gadusol的化合物，這種化合物會對陽光中的紫外線產(chǎn)生防御效果?！俺溉閯游锿獾拇蠖鄶?shù)脊椎動物，都有負(fù)責(zé)產(chǎn)生gadusol的基因?！?馬哈茂德說。迄今他們已證實，只有斑馬魚實際利用了這種化合物來抵御紫外線。不過，現(xiàn)在科學(xué)家正在研究人類能否利用此基因特征防止皮膚曬傷。

為什么我們和其他哺乳動物不會產(chǎn)生gadusol呢？“有說法稱，早期哺乳動物是夜間活動的。是不是因為它們失去了產(chǎn)生gadusol的基因呢？我們不得而知?！?馬哈茂德說道，“毛皮和厚皮是不是它們進(jìn)化后期出現(xiàn)的？把這個問題搞清楚，我想會挺有意思。”

失去gadusol生成能力的哺乳動物不甘示弱，它們發(fā)展了自身特有的復(fù)雜保護(hù)機(jī)制。我們知道河馬會從毛孔分泌出一種血狀的紅色液體。然而，《自然》雜志的一份報告稱，直到2004年，一群日本科學(xué)家才發(fā)現(xiàn)，覆在河馬皮膚上的這層液體所含的橙紅色化合物可以防御紫外線。其他動物則把防曬重點放在身體最脆弱的部位上。例如，長頸鹿的舌頭會產(chǎn)生較多的保護(hù)性黑色素，因此舌頭顏色較深。之所以如此，是因為長頸鹿要取食樹上的嫩葉，舌頭長期暴露在烈日下。

那么，動物究竟會曬傷嗎？會的?！昂Ｑ蟛溉閯游?，尤其是鯨類動物（鯨、海豚和鼠海豚）就是例外，因為它們既沒有毛皮，也沒有鱗甲。” 阿塞韋多-懷特豪斯說。她研究鯨的曬傷現(xiàn)象已有五年多時間。

從跨洋遷徙的藍(lán)鯨、抹香鯨和長須鯨背上采集的皮膚樣本中，阿塞韋多-懷特豪斯和她的同事們發(fā)現(xiàn)了曬傷的痕跡，鯨間或會浮上海面呼吸和相互交流，曬傷就是在那些時候造成的。而至關(guān)重要的是，他們還發(fā)現(xiàn)鯨有專門對抗這類曬傷的機(jī)制?！蚌L類動物共有的適應(yīng)機(jī)制是它們似乎具備非常有效的損傷修復(fù)能力?！?阿塞韋多-懷特豪斯說。

一些鯨會產(chǎn)生色素，使皮膚顏色變深，為皮膚提供保護(hù);另一些鯨體內(nèi)的基因會在皮膚內(nèi)觸發(fā)保護(hù)性應(yīng)激反應(yīng)。有的鯨甚至還進(jìn)化出堅硬的角化層，以保護(hù)下層的脆弱皮膚?！拔覀兗拥匕l(fā)現(xiàn)，沒有任何實質(zhì)證據(jù)表明鯨會罹患皮膚癌?！?阿塞韋多-懷特豪斯說?，F(xiàn)在，他們正試圖確切掌握這些修復(fù)機(jī)制的作用原理。

從防護(hù)涂層、自制防曬霜，到快速修復(fù)，這些動物用各種巧妙手段抵御日曬，也許有朝一日能給予我們啟發(fā)，幫助我們拯救自己的皮膚。

（譯者為“《英語世界》杯”翻譯大賽獲獎?wù)撸?/p>