研究揭露蝙蝠演化史，可追溯至6500萬年前

作者：威爾・丹漢（Will Dunham）By Will Dunham

華盛頓，9月24日（路透社）—— 蝙蝠是全球生態系中的關鍵角色，能為植物授粉、傳播種子，並吃掉大量昆蟲。在地球史上僅有的三支飛行脊椎動物譜系中，蝙蝠是其中之一；現今存活的蝙蝠物種超過1500種。但牠們的演化史，對科學家而言一直有些令人費解。WASHINGTON, Sept 24 (Reuters) - Bats are critical players in global ecosystems, pollinating plants, dispersing seeds and eating huge numbers of insects. One of only three lineages of flying vertebrates in Earth's history, there are more than 1,500 bat species living today. But their evolutionary history has been a bit of a puzzle for scientists.

如今，迄今規模最大的蝙蝠基因組與化石綜合研究，正讓這段歷史變得較為清晰。研究結果顯示，這些飛行哺乳動物最早約於6500萬年前出現在歐洲，也就是導致恐龍滅絕的大滅絕事件之後，隨後才擴散到世界各地；這與先前認為牠們起源於北美、亞洲或非洲的假說不同。The largest combined bat genome and fossil study ever conducted is now bringing some clarity. Its findings indicate that these flying mammals first appeared in Europe about 65 million years ago, in the aftermath of the mass extinction event that doomed the dinosaurs, before spreading around the world, not in North America, Asia or Africa as previously hypothesized.

研究人員彙整了迄今規模最大的高品質蝙蝠基因組資料，涵蓋代表所有21個公認蝙蝠科的103個物種。他們將這些資料與44件蝙蝠化石的分析整合，以解讀蝙蝠的演化史，並建立蝙蝠家族樹。The researchers assembled the largest collection of high-quality bat genomes to date, covering 103 species representing all 21 recognized families of bats. They integrated this data with an analysis of 44 fossil bats to decipher their evolutionary history and generate a bat family tree.

他們也得出結論：如同飛行能力一樣，回聲定位——許多蝙蝠用來在黑暗中導航並捕捉飛行獵物的生物聲納系統——是在蝙蝠演化初期附近演化而來。They also concluded that, like flight, echolocation — the biological sonar system many bats use to navigate in the dark and catch flying prey — evolved near the dawn of bat evolution.

本週刊登於《自然》（Nature）期刊的這項研究，其共同主持人之一、蘇格蘭聖安德魯斯大學（University of St Andrews）生物學教授桑雅・維尼斯（Sonja Vernes）表示：「我認為，同時能飛行又能回聲定位，開啟了進入新生態棲位的驚人機會——例如在夜間狩獵，當時競爭較少、掠食者也較少。飛行讓牠們進入空中；回聲定位則讓牠們掌握黑夜。」"I think being able to do both, fly and echolocate, opens up the most amazing opportunities to move into new niches — hunting at night when there's less competition and fewer predators, for example. Flight got them into the air. Echolocation let them own the night," said Sonja Vernes, a professor of biology at the University of St Andrews in Scotland and one of the leaders of the study published this week in the journal Nature.

另一名研究主持人、都柏林大學學院（University College Dublin）動物學教授艾瑪・提林（Emma Teeling）表示：「回聲定位基本上讓蝙蝠得以成為夜行性動物，不必與鳥類競爭，也不會被日行性（白天活動）鳥類捕食。」"Echolocation allowed bats to become nocturnal, essentially, and not compete with birds or be preyed on by diurnal (day-active) birds," said zoology professor Emma Teeling of University College Dublin, another of the study leaders.

這項研究指出，蝙蝠最早約在6600萬年前一顆小行星撞擊地球後100萬年出現在歐洲；那場災變讓哺乳動物得以成為陸地上的優勢動物。另一名研究主持人、紐約州立大學石溪分校（State University of New York at Stony Brook）演化生物學家莉莉安娜・達瓦洛斯（Liliana Davalos）表示，相對不久之後，蝙蝠抵達非洲，使這兩個大陸成為早期蝙蝠演化的中心。The study pointed to bats first appearing in Europe about a million years after an asteroid struck Earth 66 million years ago, a calamity that enabled mammals to become the dominant land animals. Relatively soon thereafter, bats reached Africa, making those two continents a hub of early bat evolution, according to evolutionary biologist Liliana Davalos of the State University of New York at Stony Brook, another of the study leaders.

南極洲是唯一蝙蝠從未棲居過的大陸。如今，蝙蝠占全球哺乳動物物種超過五分之一。Antarctica is the lone continent bats never inhabited. They now account for more than a fifth of the world's mammal species.

目前已知最古老的蝙蝠化石可追溯至約5200萬年前。基因組與解剖資料協助判定了蝙蝠的起源時間。The oldest-known bat fossils date to approximately 52 million years ago. Genome and anatomical data helped identify the origination date of bats.

鳥類與翼龍BIRDS AND PTEROSAURS

蝙蝠是唯一達成動力飛行的哺乳動物，與名為翼龍的飛行爬行動物和鳥類並列為僅有能做到這點的脊椎動物。鳥類在小行星撞擊後存活下來，但翼龍沒有。翼龍滅絕可能開啟了可由新的飛行脊椎動物譜系填補的生態棲位。Bats are the only mammals to have achieved powered flight, joining the flying reptiles called pterosaurs and birds as the only vertebrates to do so. Birds survived the asteroid, but pterosaurs did not. The pterosaur extinction may have opened ecological niches that a new lineage of flying vertebrates could fill.

蝙蝠翅膀的構造不同於鳥類與翼龍；它們是特化的前肢，具有大幅延長的手指，用來支撐大片皮膜。Bat wings, built differently than those of birds and pterosaurs, are modified forelimbs featuring greatly elongated fingers that support a large skin membrane.

蝙蝠祖先的外貌仍是謎團。What the ancestors of bats looked like remains a mystery.

提林表示：「我們並不確定，但我猜牠們看起來像開始長出長手指的樹鼩。這只是猜測，因為所有最古老的化石看起來都像現代蝙蝠。」"We don't know for sure but I reckon they looked like tree shrews starting to grow long fingers. This is just a guess as all of the oldest fossils look like modern bats," Teeling said.

目前也不清楚飛行能力與回聲定位何者先演化出來。蝙蝠使用回聲定位時，會發出高頻超音波聲響，並聆聽物體反射回來的回音，以描繪周遭環境。這種能力可根據化石中的解剖特徵看出，例如擴大的耳蝸以及特化的中耳構造。It also is unclear whether flight or echolocation evolved first. Bats use echolocation by making high-frequency ultrasonic sounds and listening to the returning echoes bouncing off objects to chart their surroundings. This ability can be seen in fossils based on anatomical traits such as an enlarged cochlea and specialized middle ear structures.

提林表示：「我們最古老的蝙蝠化石顯示，牠們同時具備飛行與回聲定位能力，這無助於回答這個問題。我們需要找到最古老的『前蝙蝠』，也就是過渡化石，看看牠們是否具有顯示飛行或回聲定位的解剖特徵。」"Our oldest bat fossils show that they had both flight and echolocation capabilities, which doesn't help answer this question. We need to find the oldest 'pre-bats,' or transition fossils, and see if they had anatomical characteristics indicative of flight or echolocation," Teeling said.

許多蝙蝠物種展現出顯著的抗病能力，並且以牠們的體型而言壽命格外長。這項研究為探究這些特徵的遺傳基礎奠定了基礎。Many bat species show remarkable resistance to disease and live exceptionally long lives for their size. The study lays the groundwork for research into the genetic basis of these traits.

提林表示：「這項工作最終可能為人類在老化、免疫與抗病力方面的研究提供參考。」"This work could eventually inform human research into aging, immunity and disease resistance," Teeling said.

現今蝙蝠的形態與體型多樣，食性與生活方式也各不相同。最大的是菲律賓的金冠大狐蝠，翼展達5.5英尺（1.7公尺）。最小的是泰國與緬甸的豬鼻蝠，翼展約5英寸（13公分）。Bats today come in many shapes and sizes, with differing diets and lifestyles. The largest is the giant golden-crowned flying fox of the Philippines, with a wingspan of 5-1/2 feet (1.7 meters). The smallest is the bumblebee bat of Thailand and Myanmar, with a wingspan of about 5 inches (13 cm).

許多蝙蝠以昆蟲為食。其他蝙蝠則食用水果、花蜜、魚類；而吸血蝠則惡名昭彰地以血為食。Many bats are insectivores. Others consume fruit, nectar, fish and, infamously in the case of vampire bats, blood.

蝙蝠種類極其多樣，包括馬蹄蝠、葉鼻蝠、鼠尾蝠、三叉蝠、鬼面蝠、鬚蝠、吸盤足蝠、錘頭果蝠與皺面蝠等。There is an amazing array, including the likes of horseshoe bats, leaf-nosed bats, mouse-tailed bats, trident bats, ghost-faced bats, mustached bats, sucker-footed bats, hammer-headed bats and wrinkle-faced bats.

維尼斯表示：「蝙蝠不斷讓我們驚訝。牠們是演化最偉大的實驗之一。」"Bats constantly surprise us. They're one of evolution's greatest experiments," Vernes said.

（威爾・丹漢報導；丹尼爾・沃利斯編輯）(Reporting by Will Dunham; Editing by Daniel Wallis)