它是一種黑熊,但卻天生雪白毛皮。它生活在大熊雨林中,受到當(dāng)?shù)赝林用竦母叨缺Wo(hù)。相比普通的黑熊,它是捕魚能手。它皮毛變白是因?yàn)殡[形基因突變,但科學(xué)家們至今也無(wú)法確定這種基因突變的起因。這種極為珍稀的動(dòng)物被稱為“白靈熊”,也叫“克莫德熊”。讓我們跟隨作者進(jìn)入神秘幽暗的叢林,一起尋找這種精靈之熊吧!
By Bruce Barcott
經(jīng)緯 選編 Wendy 譯注
With a wildlife guide, I stepped on a journey to find one of the rarest creatures in the world—the spirit bear, a walking contradiction—a white black bear. Neither albino nor polar bear, the spirit bear (also known as the Kermode bear[1]) is a white variant of the North American black bear, and it’s found almost exclusively here in the Great Bear Rainforest. At 25,000 square miles—one and a half times as big as Switzerland—the region runs 250 miles down Canada’s western coast. It also consists of a vast network of mist-shrouded fjords, densely forested islands, and glacier-capped mountains. Grizzlies, black bears, wolves, wolverines, humpback whales, and orcas thrive along this coast. It’s a spooky[2], wild, mysterious place: there are wolves here that fish. Deer that swim. Western red cedar trees that have stood a thousand years. And a black bear that is white. At first we did not see any spirit bear. My guide Robinson scanned for movement. No bears. But then he spotted a tuft of white fur snagged on an alder branch. “They’re around here, for sure,” he said. He pointed to the chewed bark. “They like to stand and bite the tree just to say to other bears, I’m here using this river.” An hour passed. Robinson and I waited patiently on top of a moss-patched boulder. Then he heard a rustling in the bush. “There he is,” he said. A white bear stepped out of the tree cover onto a streamside rock. Set against the dark rain forest, the bear’s fur appears shabbily radiant. Not pure white, exactly. More like a vanilla-colored carpet in need of a steam cleaning. The bear swung its head from side to side, peering into an eddy for salmon. Before it can lunge for[3] one, a black bear suddenly comes out of the forest and runs the white bear off its perch—though “runs” might be a bit strong. Everything the bears do seems to unfold in slow motion, as if they’re trying to conserve every last calorie for the coming winter. The white bear lumbers[4] into a thicket and disappears. Robinson watches. He’s spent 15 years among the spirit bears. Still, he’s transfixed. “This particular white bear is very submissive,” he says. “Sometimes that gets to[5] me. I’m protective. I once saw an old white bear attacked by a younger black bear. I was about to jump in and pepper spray the black one. The instinct was strong in me. But then the white one reared up and threw him off.” Robinson smiles. Robinson isn’t alone. That same protective instinct runs strong throughout the Great Bear Rainforest. It’s one of the factors that have kept the spirit bear alive. “Our people never hunted the white bear,” said a native clan matriarch. Bear meat was rarely a main food, though they went after black bear in greater numbers when European merchants established the British Columbian fur trade in the late 18th century. Even in those days, taking a white bear was taboo, a tradition that has continued through many generations. “We never even spoke of the spirit bear at the dinner table,” she said. Scientists know how black bears are born white. They’re just not sure why. The phenomenon, known as Kermodism, is triggered by a recessive mutation at the MC1R gene, the same gene associated with red hair and fair skin in humans.[6] To be born white, a bear must inherit the mutation from both parents. The parents themselves don’t have to be white. They just need to carry the recessive mutation. So it’s not uncommon for white bears to be born to black parents. White fur happens in only one of every 40 to 100 black bears on the British Columbia mainland coast, but the trait is especially distinct on certain islands in the Great Bear Rainforest. For example, on Princess Royal Island, one in ten black bears is white, and on Gribbell Island, directly north of Princess Royal, it’s one in three. It’s unclear how the trait arose. One theory was the “glacial bear” hypothesis that the spirit bear represented a remnant adaptation from the last great ice age, which ended here 11,000 years ago. At that time most of modern-day British Columbia was still icebound, and a white coat may have offered camouflage. But the “glacial bear” theory raised a question: Why didn’t the white fur trait die out when the glaciers receded? Researchers have recently proved that the spirit bear’s white coat gives it an advantage when fishing. Although white and black bears tend to have the same success rate after dark, there is a difference during the daytime. White bears catch salmon in one-third of their attempts. Black individuals are successful only one-quarter of the time. “The salmon are less concerned about a white object as seen from below the surface,” a scientist speculates. That may answer part of the question about why the white-fur trait continues to flourish today. If salmon are a coastal bear’s primary fat and protein source, a successful female can feast on salmon to store more fat for winter, potentially increasing the number of cubs she can produce. As the rain continued to fall on Princess Royal Island, we watched the spirit bear feed on a bounty of salmon. When the pickings are good, bears can turn finicky. Some eat only the fish head. Others may slit the belly and suck out the eggs. Some are gluttons. We observed the scene for hours, until daylight faded from the sky. |
跟隨一位野生動(dòng)物向?qū)В姨ど狭藢ふ沂澜缟献钕∮械膭?dòng)物之一“白靈熊之旅”。它是一個(gè)活著的矛盾體:一種長(zhǎng)著雪白皮毛的黑熊。白靈熊(也被稱為“克莫德熊”)既不是白化病患者,也不是北極熊家族的成員。它是北美黑熊的一個(gè)白色變種,幾乎全部都生活在大熊雨林中。大熊雨林覆蓋面積達(dá)25,000 平方英里,是瑞士國(guó)土面積的1.5倍,它沿著加拿大西海岸延綿250英里。這片雨林覆蓋了大片薄霧繚繞的峽灣、樹(shù)木繁茂的島嶼和冰川蓋頂?shù)纳矫}?;倚堋⒑谛?、狼、狼獾、座頭鯨和虎鯨在這片海岸繁衍生息。這是一個(gè)陰森原始的神秘之所:狼在這里捕魚,鹿在這里游泳,這里的西部紅雪松生長(zhǎng)了千年之久,而黑熊也披上了白衣。 最先我們并沒(méi)有看見(jiàn)白靈熊。我的向?qū)斮e遜仔細(xì)搜尋了各種蛛絲馬跡,都沒(méi)有發(fā)現(xiàn)它們的蹤跡。隨后他發(fā)現(xiàn)了一撮白毛掛在一根榿木枝上?!八鼈兙驮诟浇?,我敢肯定。”他指著被咬過(guò)的樹(shù)皮說(shuō):“它們喜歡站起來(lái)啃樹(shù)皮,以此來(lái)告訴其他同伴,這條河是我的地盤。”一小時(shí)過(guò)去了,我和魯賓遜仍在一塊布滿苔蘚的巨石上耐心地等待著。然后,他聽(tīng)到灌木叢中沙沙作響。他說(shuō):“就在那兒?!?/p> 一頭白靈熊從樹(shù)叢中走了出來(lái),來(lái)到河邊的一塊石頭上。在幽暗雨林背景的襯托下,它的毛發(fā)著微光。嚴(yán)格來(lái)說(shuō),并非純白色,更像是一塊需要溪水沖洗的香草色地毯。這頭白靈熊把腦袋從一邊甩到另一邊,緊盯著渦流中的鮭魚。正當(dāng)它要撲入水中捉魚時(shí),一頭黑熊突然從森林里竄了出來(lái),把白靈熊從石頭上沖了下來(lái)。不過(guò),用“沖”這個(gè)詞或許有些夸張。這兩只熊的每一個(gè)動(dòng)作就像是慢鏡頭般展現(xiàn)在眼前,它們好像是為了即將到來(lái)的寒冬而努力多保留最后的每一分熱量。白靈熊慢吞吞地走進(jìn)叢林,消失了。 魯賓遜目睹了整個(gè)過(guò)程。他與白靈熊打交道已經(jīng)有15個(gè)年頭了,但依然是當(dāng)場(chǎng)愣住了。“這頭白靈熊太溫順了,”他說(shuō),“有時(shí)候我很擔(dān)憂。我保護(hù)意識(shí)很強(qiáng)。有一次,我看到一頭年邁的白靈熊受到一頭年輕黑熊的攻擊。我?guī)缀蹙鸵獩_過(guò)去,用胡椒粉噴霧趕走那只黑熊。我內(nèi)心的這種本能意識(shí)很強(qiáng)。然而就在這時(shí),那只白靈熊用后腿直立,擊敗了黑熊?!濒斮e遜微笑著。 并非魯賓遜一人有這樣的感覺(jué)。在整個(gè)大熊雨林地區(qū),人們懷有強(qiáng)烈的保護(hù)白靈熊的本能意識(shí),這也是白靈熊能夠繁衍生息的一個(gè)原因?!拔覀儚膩?lái)不獵殺白靈熊,”當(dāng)?shù)匾晃慌柯涞淖彘L(zhǎng)如是說(shuō)。當(dāng)?shù)厝撕苌倌眯苋庾髦魇?。雖然在18世紀(jì)后期,歐洲商人在不列顛哥倫比亞省進(jìn)行毛皮貿(mào)易時(shí),當(dāng)?shù)卦∶裨C殺過(guò)大量的黑熊。但即便在那時(shí),捕殺白靈熊也是一種禁忌,這是一個(gè)代代傳承的傳統(tǒng)。“我們甚至從未在餐桌上提起過(guò)白靈熊,”她說(shuō)。 科學(xué)家知道黑熊如何生出白毛,但他們不能確定具體原因。這種現(xiàn)象被稱為“克莫德現(xiàn)象”,是由黑素皮質(zhì)素受體1基因的一種隱性突變引發(fā)所致。在人類身上,這種基因與紅頭發(fā)和白皮膚有關(guān)。小熊必須繼承父母雙方的變異基因,才能夠天生白毛。而父母自己的皮毛并非一定是白色的,只需攜帶這種隱性突變基因即可,因此黑熊父母生出小白熊并不稀奇。 在不列顛哥倫比亞省大陸海岸,每40頭到100頭黑熊中,只有一頭白毛熊出現(xiàn)。相比之下,這一現(xiàn)象在大熊雨林的部分島嶼上卻尤為明顯。例如,在大公主島上,十頭黑熊中便有一頭是白靈熊;在大公主島正北方的科里布島上,這個(gè)比例更是高達(dá)三分之一。 這種遺傳特征的起源仍舊是一個(gè)謎。有一種理論叫“冰川熊”假說(shuō):認(rèn)為白靈熊代表了1.1萬(wàn)年前最后一個(gè)冰河時(shí)代殘留下來(lái)的一種適應(yīng)性變異。那時(shí),如今的不列顛哥倫比亞省的絕大多數(shù)地區(qū)都被冰雪覆蓋,白色的皮毛可能會(huì)提供很好的偽裝。但“冰川熊”理論也提出了一個(gè)疑問(wèn):為什么這種白色毛皮的特征沒(méi)有隨著冰川的消退而消失? 研究者們最近證實(shí),白靈熊的白色皮毛使其在捕魚時(shí)更具優(yōu)勢(shì)。盡管白靈熊和黑熊在天黑后捕魚的成功率差不多,但在白天卻有所不同:白靈熊捕捉鮭魚的成功率為三分之一,而黑熊此時(shí)的幾率僅為四分之一?!磅q魚從水面之下往上看時(shí),對(duì)白色物體倒不大在意,”一位科學(xué)家推測(cè)說(shuō)。這在一定程度上也解釋了白色皮毛特征延續(xù)至今的原因。如果鮭魚是生活在岸邊的熊的主要脂肪和蛋白質(zhì)來(lái)源,白靈母熊又能成功捕食鮭魚,為冬季儲(chǔ)存更多的脂肪,那么就可能提高其產(chǎn)崽量。 大公主島上的雨仍下個(gè)不停,我們正在觀看一頭白靈熊大量地捕食鮭魚。當(dāng)河里鮭魚數(shù)量充足時(shí),熊就會(huì)變得很挑剔。有的只吃魚頭,有的則撕開(kāi)魚肚,只吸食里面的魚籽,還有一些熊則狼吞虎咽。我們觀察這一景象達(dá)幾小時(shí)之久,直至日光從天幕中漸漸消逝。 (來(lái)源:英語(yǔ)學(xué)習(xí)雜志) |
Vocabulary: 1. Kermode bear: “克莫德熊”之名取自一位研究此物種的加拿大人弗蘭西斯?克莫德(Francis Kermode)。 2. spooky: 陰森森的,怪異得使人害怕的。 3. lunge for: 猛沖,猛撲過(guò)去。 4. lumber: 笨重地行進(jìn),行動(dòng)遲鈍。 5. get to: 〈美俚〉使擔(dān)心,使沮喪。 6. recessive mutation: 隱形基因突變;MC1R: 黑素皮質(zhì)素受體1基因,是控制動(dòng)物黑色素合成的重要基因。 |