Pheidole dentata, a native ant of the south-eastern U.S., isn't immortal. But scientists have found that it doesn't seem to show any signs of aging. Old worker ants can do everything just as well as the youngsters, and their brains appear just as sharp. 'We get a picture that these ants really don't decline' says Ysabel Giraldo, who studied the ants for her doctoral thesis at Boston University.

尖齿大头蚁是一种美国东南部的本土蚂蚁，它们并不能一直存活下去。但科学家发现这种蚂蚁似乎不会展现出任何衰老的迹象。年老的工蚁和年轻的工蚁一样可以做任何事情，而且它们的大脑同样敏锐。伊莎贝尔·吉拉尔多的波士顿大学博士论文的主题是有关这种蚂蚁的，她说:“我们得到的图像显示这些蚂蚁并没有任何衰老的迹象。

Such age-defying feats are rare in the animal kingdom. Naked mole rats can live for almost 30 years and stay fit for nearly their entire lives. They can still reproduce even when old, and they never get cancer. But the vast majority of animals deteriorate with age just like people do. Like the naked mole rat, ants are social creatures that usually live in highly organised colonies. 'It's this social complexity that makes P. dentata useful for studying aging in people', says Giraldo, now at the California Institute of Technology. Humans are also highly social, a trait that has been connected to healthier aging. By contrast, most animal studies of aging use mice, worms or fruit flies, which all lead much more isolated lives.

这种抗衰老的能力在动物界是很罕见的。裸鼹鼠可以存活近30年，且几乎一生都保持着健康。即使已经老了，它们仍然可以繁衍后代，而且永远不会得癌症。但绝大多数的动物会像人类一样，随着年龄的增长，身体会衰弱。和裸鼹鼠一样，蚂蚁也是群居动物，它们通常生活在非常有序的群体中。加州理工学院的吉拉尔多说:“正是这种社会复杂性使尖齿大头蚁有助于研究人类衰老。“人类也是高度社会化的，这一特性与更加健康的衰老相关联。相比之下，大多数有关衰老的动物研究使用的是老鼠、蠕虫或者果蝇，但它们都过着相对孤立的生活。

In the lab, P. dentata worker ants typically live for around 140 days. Giraldo focused on ants at four age ranges: 20 to 22 days, 45 to 47 days, 95 to 97 days and 120 to 122 days. Unlike all previous studies, which only estimated how old the ants were, her work tracked the ants from the time the pupae became adults, so she knew their exact ages. Then she put them through a range of tests.

在实验室里，尖齿大头工蚁一般能存活140天左右。吉拉尔多研究了4个年龄段的蚂蚁:20-22天45-47天、95-97天和120-122天。之前的所有研究只估算蚂蚁的年龄，而她的研究却有所不同，她从蛹成年后就开始追踪，因此她知道蚂蚁的确切年龄。之后再对它们进行了一系列的测试。

Giraldo watched how well the ants took care of the young of the colony, recording how often each ant attended to, carried and fed them. She compared how well 20-day-old and 95-day-old ants followed the telltale scent that the insects usually leave to mark a trail to food. She tested how ants responded to light and also measured how active they were by counting how often ants in a small dish walked across a line. And she experimented with how ants react to live prey: a tethered fruit fly. Giraldo expected the older ants to perform poorly in all these tasks. But the elderly insects were all good caretakers and trail-followers — the 95-day-old ants could track the scent even longer than their younger counterparts. They all responded to light well, and the older ants were more active. And when it came to reacting to prey, the older ants attacked the poor fruit fly just as aggressively as the young ones did, flaring their mandibles or pulling at the fly's legs.

吉拉尔多观察了蚂蚁如何照顾蚁群的幼蚁，记录每只蚂蚁照顾、转移和喂养幼蚁的频率。她比较了20天大的蚂蚁和95天大的蚂蚁是如何通过昆虫通常为寻觅食物留下的气味而追踪它们的情况。她测试了蚂蚁对光线的反应，并通过计算一个小碟子里的蚂蚁沿线活动的频率来测量它们的活跃程度。她还试验了蚂蚁对生物饲料--一只拴着的果蝇--的反应。吉拉尔多预计年长的蚂蚁在这些任务中表现不佳。但年长的蚂蚁是很好的看护者和追踪者-95天大的蚂蚁比年轻的蚂蚁追踪气味的时间更长。它们对光线的反应都很好，年长的蚂蚁更活跃。当谈到对猎物的反应时，年老的蚂蚁会像年轻蚂蚁一样攻击可怜的果蝇，它们也会张大下颚或者去拉拽果蝇的腿。

Then Giraldo compared the brains of 20-day-old and 95-day-old ants, identifying any cells that were close to death. She saw no major differences with age, nor was there any difference in the location of the dying cells, showing that age didn't seem to affect specific brain functions. Ants and other insects have structures in their brains called mushroom bodies, which are important for processing information, learning and memory. She also wanted to see if aging affects the density of synaptic complexes within these structures—regions where neurons come together. Again, the answer was no. What was more, the old ants didn't experience any drop in the levels of either serotonin or dopamine—brain chemicals whose decline often coincides with aging. In humans, for example, a decrease in serotonin has been linked to Alzheimer's disease.

随后吉拉尔多比较了20天大的蚂蚁和95天大的蚂蚁的大脑，找出了濒临死亡的细胞。她没有发现年龄的主要差异，死亡细胞的位置也没有任何差异这表明年龄似乎不会影响特定的大脑机能。蚂蚁和其他昆虫的大脑中有一种被称为蕈形体的结构，这种结构对昆虫生存中处理信息、学习和记忆都很重要。她还想看看衰老是否会影响这些结构中突触复合体的密度--神经元聚集的区域。答案还是否定的。更重要的是，年长蚂蚁的血清素和多巴胺水平都没有下降，而这两种大脑中的化学物质的下降往往伴随着衰老。例如，在人体内，血清素的减少与阿尔茨海默病有关。

'This is the first time anyone has looked at both behavioral and neural changes in these ants so thoroughly', says Giraldo, who recently published the findings in the Proceedings of the Royal Society B. Scientists have looked at some similar aspects in bees, but the results of recent bee studies were mixed—some studies showed age-related declines, which biologists call senescence, and others didn't. 'For now, the study raises more questions than it answers,' Giraldo says, 'including how P. dentata stays in such good shape.'

吉拉尔多说:“这是第一次有人对这些蚂蚁的行为和神经的变化研究得如此彻底。”，她最近在《英国皇家学会学报B》发表了研究结果。科学家们着眼于研究蜜蜂的一些相似方面，但最近有关的研究结果有些复杂-些研究显示其年龄相关性会下降，也就是生物学家所说的衰老，而其他一些研究却没有显示。吉拉尔多说:“到目前为止，这项研究提出的问题比它能回答的问题还多，其中包括尖齿大头蚁是如何保持这么好的状态的。

Also, if the ants don't deteriorate with age, why do they die at all? Out in the wild, the ants probably don't live for a full 140 days thanks to predators, disease and just being in an environment that's much harsher than the comforts of the lab. 'The lucky ants that do live into old age may suffer a steep decline just before dying,' Giraldo says, but she can't say for sure because her study wasn't designed to follow an ant's final moments.

此外，如果蚂蚁的机体不会随着年龄的增长而恶化，那么它们为什么会死亡呢?在野外，蚂蚁可能活不了140天，这都归咎于捕食者、疾病，以及它们的生存环境，这可比实验室的舒适条件要严酷得多。吉拉尔多说:“那些有幸活到老的蚂蚁在死亡前可能会经历一个急剧的衰老过程，但她野不敢确定，因为她的研究并不是为了追踪到蚂蚁的最后时刻。

'It will be important to extend these findings to other species of social insects' says Gene E. Robinson, an entomologist at the University of Illinois at Urbana-Champaign. This ant might be unique, or it might represent a broader pattern among other social bugs with possible clues to the science of aging in larger animals. Either way, it seems that for these ants, age really doesn't matter.

伊利诺伊大学厄巴纳-香槟分校的昆虫学家吉恩罗宾逊说:“将这些发现推广到其他群居昆虫上是很重要的。“这种蚂蚁可能是独一无二的，又或者它可能代表了一种更广泛的群居昆虫的模式，为科学地研究大型动物的衰老提供了可能的线索。不管怎样，对这些蚂蚁来说，年龄真的不重要，