大象是怎么长胖的

Elephant Teeth

Elephants don't diet, as far as we know. But their weight does fluctuate, at least for the ones who live in a zoo. Now, researchers have found that this gain and loss in an elephant's mass appears to hinge on their jaws - more specifically, the unusual way these animals replace their teeth. The results appear in the journal Mammalian Biology.

Researchers at the University of Zurich's Clinic for Zoo Animals, Exotic Pets and Wildlife were exploring how an elephant's mass tracks with its overall physique - whether the animal is jumbo-sized or svelte, for an elephant. So they gathered data on the entire population of captive elephants throughout Europe. The clinic's Marcus Clauss is a professor of comparative digestive physiology: "This was due to the commitment of a student I had at the time, who is called Christian Schiffmann, who was the driving force behind all this. Because Christian visited basically every European zoo that keeps elephants." He returned with records revealing the relative heft of the resident pachyderms. At first glance, his observations were not so surprising. "As in western societies, also in the zoo, a lot of beings tend to be less than an ideal body condition and a little bit more on the obese side. And elephants are just the same in that respect."

But a deeper dive into the data turned up something curious. "And that was that once the elephants reached what you would call adult age and adult body mass, there seemed to be something like a systematic cyclicity in the data: body mass going up and down and up and down over age." The yo-yo effect didn't sync with seasonal changes in the animals' diet. And it wasn't because some of the females were getting pregnant and then giving birth. Because the researchers saw the same thing in both breeding and nonbreeding animals. "So it must be something else. So Christian came up with the idea maybe it's related to the tooth cycle in elephants." For most mammals, us included, baby teeth are replaced by a full-sized adult set. But because elephants are so big, and their jaws have to grow to keep up, they go through six sets of chompers, each bigger than the last. And the new teeth don't wait for the old ones to fall out - they push them out from behind. During the process, there are times when both sets are present at once. It's not that the extra teeth themselves weigh so much. It's more like more teeth means more food processing.

"And that means either they can eat more during those times or they can chew better during those times. Eating more evidently gives more energy. Chewing better also gives more energy because for an herbivore, the finer the chew the more energy they can get out of their food." The ultimate confirmation of a connection between molars and mass may require the cooperation of veterinarians, who can ask their elephants to hop on a scale and say ...

参考译文

我们以为,大象不会节食,其实它们的体重确实会有波动,至少动物园里的大象是这样。现如今研究人员发现,大象体重的增减似乎和它们的大下巴有关,更确切地说,是和它们独特的换牙方式有关,这项研究结果发表在哺乳动物生物学期刊上。

苏黎世大学动物园动物、稀有宠物和野生动物诊所的研究人员对大象体重进行了研究,他们想知道大象体重波动与体形差异是否有关,毕竟有些大象魁梧高大,也有的相对苗条,于是他们收集了整个欧洲圈养大象的相关数据。诊所的比较消化生理学教授克劳斯说:这项研究源于当时我一个学生做的项目,他叫克里斯蒂安,是这项研究的主力,全欧洲的动物园,只要有大象的,他几乎跑了个遍,然后他带回了大象相对体重的数据,这些数据看上去平淡无奇:大象体重超标,略微偏胖,其实动物园里的动物都这样,甚至连很多西方国家的人也是这样。

但是仔细分析这些数据,有意思的事情出现了。一旦大象成年,体重达到成年大象的水平之后,数据就出现了有规律的循环:大象的体重会随着年龄的增长起起伏伏。大象体重的起伏和大象饮食的季节性变化并不同步,也不是因为母象怀孕生产才出现这种体重变化,研究人员发现,哺乳期和非哺乳期的大象都有这种体重变化。这其中一定另有隐情,于是克里斯蒂安突发奇想,会不会和大象的换牙周期有关。大多数哺乳动物,包括人类在内,乳牙都会被恒牙替代。但由于大象体型庞大,下颚要完全容纳新牙,得有个生长过程,因此大象的一生会换五次牙,一次比一次大。新牙并不会等到旧牙脱落之后才长出来,而是先长出来,再从后面慢慢把旧牙挤掉。换牙期间,新牙旧牙同时存在。当然,倒不是说重就重在了几颗牙,而是说,牙齿越多,食物咀嚼也会越多。

也就是说,换牙期间大象要么吃得多,要么咀嚼更充分:吃得多,能量摄取自然就多;咀嚼更充分,也会让能量摄取更多,因为对食草动物而言,嚼得越过细,从食物中获取的营养就越多。体重与换牙之间到底有无关联,要盖棺定论,最后可能还得跟兽医合作,毕竟只有兽医才能让大象跳上体重秤,张嘴看牙。

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