（图解：已经适应了藏身丛林的苏门答腊虎）
（作者为塔拉·皮里，博士后，来自英国雷丁大学人与野生动物研究组）

During my time as a zookeeper I had the privilege of working with both Sumatran and Amur tigers. If they did not both have stripes, you would think they were different species altogether.

在我担任动物园管理员期间，我很荣幸能与苏门答腊虎和阿穆尔虎共事。要不是它们身上都有条纹，你会认为它们是完全不同的物种。

The Sumatran tiger is the smallest alive today. At around 100kg, it’s “only” about the weight of a large adult male human. It is suited to the warm and wet forests of the Indonesian island of Sumatra, which is reflected in its smaller size and short, dark rusty orange coat which has many thin black stripes to conceal it in dense vegetation from their prey.

苏门答腊虎是现存最小的老虎。它的体重在100公斤左右，“只”相当于一个大号成年男性的体重。它很适合在印尼苏门答腊岛炎热潮湿的森林中生活，这一点从它较小的体型和短而呈现深铁锈橙色的毛上就能体现出来，这些毛发上有很多细细的黑色条纹，能帮助它们躲藏在茂密的植被中，不让猎物发现。

The Amur – or Siberian – tiger is much larger, averaging around 170kg (though there are historic reports of males clocking in at 300kg or more) and is now found mainly one corner of far-eastern Russia. It has a thicker but relatively pale coat, with sparse dark brown stripes, which enables it to survive in freezing and snowy winters.

阿穆尔虎（即西伯利亚虎）的体型要大得多，平均体重约为170公斤(不过历史上有重达300公斤以上的雄性个体的报道)，目前主要分布在俄罗斯远东地区的某个角落。它的皮毛更厚，但颜色相对来说比较苍白，有稀疏的深褐色条纹，这就让它能在冰天雪地的冬日里生存。

Tiger experts have long debated what such differences mean scientifically. Should the biggest of the big cats be divided into various subspecies, or are all tigers simply “tigers”?

长久以来，老虎专家们一直在争论这种差异在科学上意味着什么。是应该把这种最大的大型猫科动物分成各亚种，还是说所有的老虎都只是“老虎”而已？

It’s an issue with serious implications for conservation. About 3,500 or so tigers remain in the wild, in just 7% of their former range. And if those tigers are all the same, or if even most of them are the same, then saving individual populations matters slightly less – and tigers can be moved around to assist breeding in the wild.

这是一个会严重影响保育工作的问题。野生老虎大约还剩下3500只左右，所分布的范围只占从前的7%。而如果这些老虎全都是一样的，甚或是大部分老虎都一样，那么拯救个别种群的重要性就会稍稍降低，而老虎就可以被四处转移，以协助野外繁殖。

Traditionally, eight subspecies were considered to exist. They are the two already mentioned, plus the Bengal tiger, found mainly in India, the Indochinese, the South China tiger and then three extinct subspecies: the Bali (extinct in the 1940s) and Javan (80s), both closely related to surviving tigers on nearby Sumatra, and the Caspian tiger from Central Asia which went extinct in the 1970s.

人们在传统上认为存在八个亚种。它们是上述的两个亚种，再加上主要分布于印度、中南半岛和中国南方的孟加拉虎、印支虎、华南虎，还有就是三个已经灭绝的亚种：巴厘虎（于二十世纪四十年代灭绝）和爪哇虎（于八十年代灭绝），这两个亚种和幸存于附近苏门答腊岛上的老虎亲缘关系密切，还有来自中亚的里海虎，灭绝于二十世纪七十年代。

As genetic techniques evolved, a 2004 study found there was little genetic diversity among tigers, but enough to support the separation of subspecies. It also suggested that Indochinese tigers living on the Malayan peninsular were different enough to those living further north to warrant a ninth subspecies: the Malayan tiger.

随着遗传技术的发展，2004年的一项研究发现，老虎之间的遗传多样性很少，但足以支持亚种的分离。该研究还表明，生活在马来半岛的印支虎和生活在更北方的印支虎间存在的差异已经大到有足够的理由分立第九个亚种了：马来虎。

These ideas were contested by a group of researchers in 2015, who argued that the relative lack of variation among the mainland Asian subspecies and large overlaps in their shape, size and ecology meant that all tigers from India to Siberia or Thailand should be considered the same subspecies. The researchers called for just two recognised subspecies: the continental tiger, and the Sunda tiger, found on the various Indonesian islands.

这些观点在2015年遭到了一群研究人员的驳斥，他们的主张是，亚洲大陆的亚种间差异度相对不高，而且它们的形体、大小和所在的生态环境有很严重的重叠，这就意味着从印度到西伯利亚或泰国的所有老虎都应该被视为同一个亚种。这些研究人员呼吁只需要承认两个亚种：大陆虎，以及分布于印尼各大岛屿上的巽他虎。

However the various subspecies are classified, one of the consistent findings is that tigers follow Bergmann’s rule: a principle in zoology which states that animals within the same overall species will tend to be larger in colder environments and vice versa. The Amur tiger, for instance, benefits from the fact that larger animals are better at retaining heat as they have a smaller surface area relative to their overall mass.

无论如何划分各亚种，其中有一个发现是始终不变的，即老虎是遵循伯格曼法则的：这是动物学中的一条原则，说的是同一个物种中的动物在更寒冷的环境中体型往往会更大，反之亦然。例如，阿穆尔虎就得益于这样一个事实：体型更大的动物保温能力更强，因为相对于其总重量，它们的表面积更小。

Six genetically distinct groups

在基因上能互相区分的六个群体

This is where a new study published in the journal Current Biology fits in. Researchers from China and the US looked at the whole genomes of 32 representative tigers and found that there were indeed nine subspecies of tiger – of which six survive today. But their work also demonstrates that the various adaptations to temperature – Amur big and hairy, Sumatran small and sleek – were triggered by significant prehistoric events that changed global and local temperatures.

而发表在杂志《现代生物学》上的一项新研究恰好切题。来自中国和美国的研究人员检视了三十二只具有代表性老虎的全套基因组，然后发现老虎确实有九个亚种，其中有六个亚种存活至今。但他们的工作也证明了，为适应气温而出现的各种特征（阿穆尔虎体型大而多毛，苏门答腊虎体型小而光滑）是由改变全球和当地气温的重大史前事件触发的。

The findings confirm previous speculation that the low genetic diversity in tigers was caused by a population decline during an ice age 110,000 years ago. Thousands of years later, the earliest split from a single common ancestor species occurred between island and mainland subspecies, with the former developing a smaller body size thanks to natural sextion. The super eruption of the Sumatran volcano Toba 75,000 years ago followed by an extreme cooling period was the likely cause. Further splits into more specialised tigers reflect other significant extreme climatic changes.

这些发现证实了之前的推测，即老虎的遗传多样性低是由11万年前的一段冰河时代中种群数量减少造成的。最早从一个共同的祖先物种中分化出岛屿亚种和大陆亚种是在数千年后，前者在自然选择的作用下演化出了更小的体型。7.5万年前苏门答腊托巴火山超级喷发后的极寒时期可能是个中的原因。而进一步分化成更为特化的老虎，反映的是其他的重大极端气候变化。

This affects conservation tactics

这影响了保育策略

So why is this important in terms of tiger conservation? As past research has argued, the lack of genetic and morphological differences between mainland tigers could allow them to be managed as single subspecies. Theoretically individuals from any region, wild or captive, could be relocated to repopulate former areas or increase numbers of failing local populations. This could help to increase general tiger numbers and local genetic diversity.

那么，为什么这对于老虎的保育工作很重要呢？正如过去的研究所主张的那样，由于大陆虎之间在基因和形态方面的差异很小，可以将它们视为单一亚种来管理。从理论上讲，来自任何地区的个体（无论野生还是圈养），都可以被重新填充到从前存在过的栖息地，或是增加当地消亡中种群的数量。这可以帮助增加老虎的总数，并提高当地的遗传多样性。


Siberian tigers are bigger, hairier and have fewer stripes. Vaclav Sebek / shutterstock

（图解：西伯利亚虎更大、更重，条纹也更少）

But the recent study suggests that tiger adaptations may be more subtle and intricate than first appeared. If tigers are allowed to hybridise either in captive or wild populations it could drive the more vulnerable subspecies to extinction before we fully understand exactly how they have adapted to their particular area.

但最近的研究表明，老虎的适应性可能比最初展现出的更为微妙和复杂。如果允许老虎在圈养或野生的种群中进行杂交，那么在我们完全了解老虎是如何适应其所在的特定地区之前，此举可能会将更脆弱的亚种推向灭绝。

There is a downside to considering tigers as separate subspecies and attempting to protect them on this basis, without mixing in tigers from elsewhere. Numbers of each subspecies are very small – there are only around 500 wild Amurs, for instance – and smaller populations are more vulnerable to extinction. This could be caused by the regular threats of habitat loss and poaching or simply due to reduced genetic diversity making a small population vulnerable to disease and other sextive pressures.

将老虎视为独立的亚种，并试图在此基础上保护它们，也不将来自其他地区的老虎混入其中，也会带来一个弊端。每个亚种的数量都非常少，例如，野生的阿穆尔虎只有五百只左右，而数量较少的种群更容易灭绝。这可能是栖息地的流失和偷猎这些常态化威胁造成的，也可能只是因为遗传多样性的变少，这会使小种群易受疾病和其他选择性压力的伤害。

Genetic diversity is key for adaptation and ultimately species survival. As our understanding increases, more informed decisions can be made regarding how best to conserve the tiger. We might not have enough time to solve all the riddles but perhaps this is one step closer to ensuring one of the world’s most iconic animals does not disappear forever.

遗传多样性是适应性和最终物种生存的关键。随着我们认识的提高，我们可以对如何最好地保护老虎做出更明智的决定。我们可能没有足够的时间来解开所有的谜题，但也许这是向确保世界上最具代表性的动物之一不会永远消失迈出的一步。