狮子被称为丛林之王，但根据最近的一项研究，只须对它们喷一点催产素（oxytocin，一种已知的可以促进社会联系的激素），就能让最暴躁的“狮子王”变成一只温顺的大猫咪。研究结果发表在《交叉科学》（iScience）杂志上。美国明尼苏达大学（University of Minnesota）狮子中心（Lion Center）主任克雷格·帕克（Craig Packer）：“看狮子最棒的地方在于……狮子与狮子之间是如此坦诚、毫无保留地深情相待。”自1970年代以来，帕克就经常前往坦桑尼亚的塞伦盖蒂，研究这些大型猫科动物的社会行为。帕克：“它们会额头贴贴，把下巴埋进对方的脸里，它们真的很喜欢彼此。而当它们平静下来准备回去睡觉时，也会在一只躺倒后，另一只与它相依而眠。看起来让人心都化了。”帕克的研究生杰茜卡·伯克哈特（Jessica Burkhart）也表示：“我一直很喜欢狮子。但是，狮子与它们的近亲豹子以及它们的第二近亲老虎却完全不同，豹子和老虎完全是独居动物，狮子究竟有什么不同呢？”帕克：“催产素又被称为‘爱的荷尔蒙’，但这听起来像是某种爱情药水，我更愿称之为‘情感荷尔蒙’。如果你被给予了一个温暖的抱抱，你产生的那种突然出现的感觉，就源自催产素。所以狮子就像一个完美的物种示例，你可以在它们身上看到能用催产素做些什么。”他们在南非的一个野生动物保护区进行了这项研究，而第一个挑战是弄清楚如何让这种激素进入狮子体内。帕克说：“杰茜卡把它做成‘香水’的想法让我大吃一惊，我觉得它非常巧妙，而且效果非常好。”伯克哈特：“我们做了一种带有长长尖嘴的小玻璃瓶，还有一个用于按压给气的橡胶球，尖嘴大概有15厘米长。”伯克哈特会挥动一大块美味的肉引诱狮子来到围栏边。“一旦狮子抓住了我拿着的那块肉，我就可以把香水瓶穿过栅栏、塞进它们的鼻孔里，然后喷进去，哈哈哈哈哈。”狮子是能忍受这种鼻喷的……只要给到了它们食物。但如果肉都没了，伯克哈特再喷的话……“你应该看看它们的脸，那表情仿佛在说‘大胆！你竟嘲弄我！’它们会觉得你是在针对它！哈哈哈哈哈，非常有意思。”研究人员随后评估了催产素在几种不同行为情况下的作用。第一个是观察这种激素是否会降低狮子对玩具或零食的领地意识，通常情况下，狮子会对自身财产的保护意识非常之强，尤其是那些可以吃的东西。伯克哈特说：“它们会低吼、咆哮，会拍打、抓挠、猛咬，所以很多时候你会得到它们猛烈攻击的反应性行为，就像在说：滚开！”如果是玩具，催产素确实有助于抑制这种反应性行为，让其他狮子靠得更近。但对于它们对食物的垄断态度并没有多大影响，伯克哈特说这并非完全出乎意料。伯克哈特：“对于玩具，毕竟大家都很爱玩，你可能更愿意让你的伙伴和你一起玩。但对于食物，则是一种更原始的本能，所以在食物试验中，正是这种与生俱来的求生欲望导致了非常反应性的攻击。”催产素在一种情况下抑制了攻击性，在另一种情况下却没有，研究人员实际上因此而感到放心：这种激素不会简单地让狮子陷入呆头呆脑的状态。伯克哈特：“它不会给你的大脑带来巨大变化，更像是早上喝咖啡一样。”但如果你是一头被睾丸酮驱动的暴脾气雄狮，催产素会让你变得娴静而优雅。伯克哈特：“我震惊了，在喷过催产素几分钟后，那个家伙就完全冷静了下来。我的意思是，我们刚给它喷催产素时，它在咆哮，狂拍栅栏，完全疯了一样，大脑被睾丸酮掌控，但在几分钟后它就完全变得柔和温顺了。”
Researchers Created a Potion That Turns Loud Lions into Placid Pussycats
Karen Hopkin: This is Scientific American’s 60-Second Science. I’m Karen Hopkin.They say that lions are the king of the jungle. But a recent study shows that a single spritz of oxytocin…a hormone known to promote social bonding…renders even the most ornery alpha a total pussycat. The findings appear in the journal iScience.Craig Packer: The greatest thing about watching lions is… lions are so openly and extravagantly affectionate with each other.Packer: They just rub each other with their foreheads, their chins are in each other’s faces. I mean they’re just really into each other. And then when they calm down and it’s time to go back to sleep…one will flop down and the other will flop on top of it. So it’s very endearing.Jessica Burkhart: I’ve always loved lions.Burkhart: But what is it about lions that is so different than their closest relative the leopard, and then their next closest the tiger, who are completely solitary?Hopkin: And the first thing that came to mind was: oxytocin.Packer: They call oxytocin the love hormone. But that sounds like Love Potion Number Nine. I prefer to think of it as the affection hormone. if you have a nice warm hug, that burst of feeling you get, that’s oxytocin. And so the lions would be like a perfect example of a species where you want to see what you can do with the oxytocin.Hopkin: They conducted the study at a wildlife sanctuary in South Africa….where their first challenge was figuring out how to get the hormone into the lions.Packer: Jessica… surprised me with this perfume sprayer, which I just thought was so ingenious and it worked out really really well.Burkhart: It’s like a little glass bottle with a long tip and then there’s a bulb. So I have to pump the bulb and then the tip is about six inches long.Hopkin: Burkhart would lure a lion over to the enclosure fence by waving a tasty hunk of meat.Burkhart: Once I hold that meat and the animal’s grabbing it I can just stick it in the fence and into their nostril and spray away. [giggles]Hopkin: The cats put up with the nasal invasion…as long as they got their grub. But if Burkhart spritzed a lion after the meat was gone….Burkhart: You should see their faces. They go, huh? Like, how dare you take a cheap shot on me. They take it personally! [laughs…] Ah, it’s so funny.Hopkin: The researchers then assessed oxytocin’s effects in several different behavioral situations. The first was seeing whether the hormone would make a lion less territorial when it comes to a desirable toy or a snack. Normally, lions are pretty protective of their possessions, particularly those that can be eaten.Burkhart: They’ll growl and they’ll snarl and … they smack and they scratch and they snap. So a lot of times you will just get this sort of reactive behavior where they’re gonna lash out, to be like: Get off!Hopkin: When it came to the toys, oxytocin did help to curb that reactive behavior, allowing other lions to come much closer. But it didn’t do much for their monopolistic attitude toward meals, which Burkhart says was not entirely unexpected.Burkhart: With the toy, you know you’re playful, you might be more inclined to having your partners play with you. When you have a food object, it’s a much more primal instinct, so with the food trial, it’s that innate desire to survive that causes this very reactive aggression.Hopkin: Seeing that oxytocin suppressed aggression in one situation, but not the other, actually reassured the researchers that the hormone wasn’t just making the lions totally dopey.Burkhart: It doesn’t make your brain completely different, but it’s like drinking your coffee in the morning.Hopkin: But if you’re a testosterone-fueled grumpy Gus, it could render you almost delightfully demure.Burkhart: Oh my gosh, within minutes of the oxytocin that guy was completely chilled out. And I mean when we were giving him his oxytocin, he was growling, smacking the fence, totally insane, testosterone brain. And then he just completely mellowed out.
Burkhart, J.C. et al. (2022) “Oxytocin promotes social proximity and decreases vigilance in groups of African Lions,” iScience, 25(4), p. 104049.
doi: 10.1016/j.isci.2022.104049
封面图来源：Unsplash
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