青蛙的声音影响其求偶的偏好

This is Scientific American's 60-second Science, I'm Jason Goldman.

这里是科学美国人——60秒科学系列，我是杰森·戈德曼。

In the shadow of Huangshan Mountain in southeastern China lives a beige frog with black stripes.

在中国东南部的黄山背光处，生活着一种带有黑色条纹的浅褐色青蛙。

The concave-eared torrent frog, or Odorrana tormota, gets its name from its unusual hearing apparatus.

凹耳洪流蛙Odorrana tormota)，因其不同寻常的听觉器官而得名。

"It has kind of an ear canal-like structure like humans, and like most mammals.

“它像人类和大多数哺乳动物一样有一种类似耳道的结构。

For most frog species, the eardrums are located on the body's surface, on the lateral part of the body surface.

对于大多数蛙类来说，耳膜位于身体表面，在身体表面的侧面。

But here the eardrum is invisible because it is embedded deep inside the head, in the skull."

但凹耳洪流蛙，耳膜是看不见的，因为它深嵌在头部的头骨中。”

Biologist Albert Feng, from the University of Illinois at Urbana-Champaign.

来自伊利诺伊大学香槟分校的生物学家阿尔伯特·冯说。

Back in 2006, Feng and his colleagues discovered that this unusual anatomy allows the frogs to hear ultrasound, which includes frequencies greater than 20 Kilohertz.

早在2006年，阿尔伯特·冯和他的同事就发现，这种不同寻常的解剖结构使青蛙能够听到超声波，其中包括频率超过20千赫兹的超声波。

Biologists had always assumed that ability was restricted to some mammals because it was only known in bats, whales, dolphins, and some rodents.

生物学家一直认为这种能力仅限于一些哺乳动物，因为只知道蝙蝠、鲸鱼、海豚和一些啮齿动物有这种能力。

We can’t hear in that range.

我们听不见那个范围的声音。

The streams that the frogs live in are quite noisy, but most of those sounds are low frequency.

青蛙生活的河流非常吵闹，但大多数声音的频率都很低。

By restricting their vocalizations to the higher frequencies, including ultrasound, the frogs are better able to hear each other.

通过将它们的叫声限制在更高的频率，包括超声波，青蛙们能更好地听到彼此的叫声。

"The higher the frequency, the less that signal is distorted, or at least masked, by the ambient noise."

“频率越高，环境噪声影响下的信号失真越少或至少信号被掩盖得越少。”

In many animals, females prefer mating with larger males, usually because that's a sign of health and strength.

在许多动物中，雌性更喜欢与体型较大的雄性交配，通常是因为这是健康和力量的象征。

And bigger males tend to produce lower frequency vocalizations.

体型较大的雄性会发出较低频率的声音。

But with higher frequency calls being more effective in this habitat, Feng wondered if females might actually prefer smaller males.

但在这种栖息地，更高频率的叫声更有效，阿尔伯特·冯想知道雌性是否真的更喜欢小一点的雄性。

Over the course of several nights, the researchers captured thirty-five pairs of frogs engaged in what biologists call amplexus.

通过几个晚上的进展，研究人员捕获了35对处于生物学家所说的抱合状态的青蛙。

Which means while having sex.

也就是说正在交配的时候。

The biologists measured the length of each male, as well as the length of those males found nearby who were unlucky enough to be caught and also not having sex.

生物学家测量了每只雄性的长度，以及在附近发现的那些不幸被捕获且没有交配的雄性青蛙的长度。

Turns out, size really does matter.

事实证明，尺寸确实很重要。

"Yes, the females are very unusual in that they really prefer smaller males over larger males."

“雌性很不寻常，它们真的更喜欢小的雄性而不是大的雄性。”

Next, the researchers brought the frogs into the lab.

接下来，研究人员把青蛙带进了实验室。

Each female was placed alongside two males.

每只雌性被放在两只雄性旁边。

Here, too, females opted to mate with smaller-bodied males.

在这里，雌性也选择与体型较小的雄性交配。

And an analysis of the mating calls showed that the smaller males did use higher frequency sounds.

对求偶叫声的分析表明，体型较小的雄性确实使用频率更高的声音。

The study was published in the Journal of Zoology.

这项研究发表在《动物学杂志》上。

"We are thinking by females preferentially choosing small-sized males, that actually we can see the trend over generations…you can see the gradual evolutionary changes in the trait.

“我们认为雌性会优先选择体型较小的雄性，实际上我们可以在几代蛙中看到这种趋势……你可以看到这一特征的逐渐进化。”

Over multiple generations you gradually develop these ultrasonic capabilities."

经过几代，会逐渐发展这些超声波能力。”

What isn't clear yet is whether the females are visually assessing the males for their size, or whether they just have an easier time hearing their higher-frequency calls—making them more likely to mate with smaller males.

目前尚不清楚的是，雌性是通过视觉判断雄性的体型，还是因为更容易听到它们高频的叫声，从而更有可能与体型较小的雄性交配。

That's exactly what Feng's team is testing now, by broadcasting mating calls to the females in a laboratory—with the lights out.

这正是阿尔伯特·冯的团队现在正在测试的，他们在实验室里关灯向雌性青蛙出交配信号。

Thanks for listening for Scientific American's 60-second Science. I'm Jason Goldman.

感谢收听《科学美国人》60秒科学节目。 我是杰森·戈德曼。