(单词翻译:单击)
听力文本
This is Scientific American — 60-Second Science. I'm Jason Goldman.
Monarch butterflies depend on milkweed. They lay their eggs on milkweed, and their caterpillars eat only the leaves of the plant. No milkweed means no monarchs. So the best way to help declining monarch populations—and to preserve their epic, multi-generational migration—is to plant milkweed.
Seems simple, right? But the reality is far more complicated.
Milkweed is slightly toxic—the plant evolved its noxious substances to keep herbivores from chowing down on the leaves. But monarch butterflies evolved tolerance. In fact, they arm themselves with the stuff.
"Monarchs sequester these toxins as an anti-predator defense and sort of anti-parasite defense."
Louisiana State University biologist Matt Faldyn.
So, by ingesting the toxin, the caterpillars become toxic themselves. That keeps them safe—as long as they don't ingest too much of the poison. The problem is there are different types of milkweed. And one that's native to the tropics is now growing in the southern U.S. As these plants sense warming temperatures, they produce more of the toxin—so much more that the monarch butterflies begin to suffer.
To gauge the threat, Faldyn and his team raised monarchs on either the non-native tropical milkweed or on a native milkweed. And they also tested the effects of current environmental conditions as well as temperatures expected for the southern U.S. by the year 2080.
Monarchs that ate native milkweed had comparable survival rates at both current and higher temperatures. But under those future warmer conditions, monarchs raised on the tropical milkweed survived at only one fifth the rate of butterflies raised under current conditions.
The monarchs could thus find themselves in what's known as an ecological trap. The butterflies seek out milkweed, but what is already the most common type of milkweed in the southern U.S. will eventually kill them.
The tropical species is prettier than the native ones, which is why many people prefer to plant it. But there's still time to change that.
"What we sort of show is that maybe there should be more of a focus on having native species to your area sort of preferentially planted in your gardens."
By switching to the native species, home gardeners across the country can each do their part to ensure that monarch butterflies will avoid fluttering their way into the ecological trap—which could be fatal.
Thanks for listening for Scientific American — 60-Second Science. I'm Jason Goldman.
参考译文
这里是科学美国人——60秒科学。我是杰森·古德曼。
帝王蝶以乳草为食。它们将卵产在乳草上，孵化出的幼虫只吃乳草的叶子。没有乳草就意味着没有帝王蝶。因此，防止帝王蝶种群数量下降并保持其史诗般多代迁徙的最佳方式就是种植乳草。
听起来很简单，对吧？但实际情况要复杂得多。
乳草有轻微毒性，这种植物进化出有害物质是为了防止食草动物吃它的叶子。而帝王蝶进化出了耐受性。实际上，它们以此来武装自己。
“帝王蝶隔离这些毒素，将其作为反捕食防御和抗寄生虫防御。”
路易斯安那州立大学的生物学家马特·菲尔德林说到。
因此，通过食入这些毒素，帝王蝶幼虫自己也会中毒。这可以保证它们的安全——只要它们不摄入太多毒素。问题是乳草有很多种类。一种原产于热带的乳草现在却生长在美国南部地区。由于这些乳草感受到了温度的长高，所以它们会产生更多毒素——多到帝王蝶难以承受。
为了评估威胁程度，菲尔德林和团队用非本土热带乳草和本土乳草分别饲养帝王蝶。他们还测试了当前环境条件以及2080年美国南部地区的预计温度所带来的影响。
在当前气温和更高气温条件下，食用本地乳草的帝王蝶的存活率相似。但那些吃热带乳草的帝王蝶，在未来较高气温条件下的存活率只有当前气温条件的五分之一。
帝王蝶因此可以发现自己处于所谓的“生态陷阱”之中。帝王蝶寻找乳草，但美国南部最常见的乳草种类最终会杀死它们。
就乳草来说，热带品种比本地品种更漂亮，这就是许多人更喜欢种植热带品种的原因。但是现在改变这种情况还来得及。
“我们想说明，也许更应该关注的是，在花园中优先种植本地品种的植物。”
通过切换到本地品种，全国各地的家庭园丁可以各尽其能，确保帝王蝶不会进入生态陷阱，这种陷阱可能是致命的。
谢谢大家收听科学美国人——60秒科学。我是杰森·古德曼。
译文为可可英语翻译，未经授权请勿转载！
重点讲解
重点讲解：
1. depend on 依靠；依赖；
Many farmers have to depend on subsidies to make a living wage.
许多农民的基本生活工资要靠补贴来维持。
2. as long as 只要；
There will be no further costs as long as the bank is part of the giro network.
只要该银行属于直接转账系统，就不会额外收取费用。
3. seek out 寻找到；找出；
Children seek out regularities and rules in acquiring language.
儿童在学习语言过程中会找出各种规律和规则。
4. do one's part 尽本份，尽职责，尽力；
If everyone do his part, the project will surely is a success.
如果大家都尽责，这个项目肯定会成功。
