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科学美国人60秒:青蛙的声音

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中英对照 听力原文

Frog Vocals Lead to Small Preference

青蛙的声音

In the shadow of Huangshan Mountain in southeastern China lives a beige frog with black stripes. The concave-eared torrent frog, or Odorrana tormota, gets its name from its unusual hearing apparatus.

在中国东南部的黄山山阴下,生活着一种带有黑色条纹的米色青蛙。凹耳激流蛙,又名臭蛙,得名于它不寻常的听觉装置。

"It has kind of [an] ear canal-like structure like humans, and like most mammals. For most frog species, the eardrums are located on the body's surface, on the lateral part of the body surface. But here the eardrum is invisible because it is embedded deep inside the head, in the skull."

“它有一种类似于人类和大多数哺乳动物的耳道结构。对于大多数蛙类来说,耳膜位于身体表面,在身体表面的外侧。但在这种青蛙身上,耳膜是看不见的,因为它深嵌在头部颅骨内。”

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艾尔伯特·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. Biologists had always assumed that ability was restricted to some mammals because it was only known in bats, whales, dolphins, and some rodents. We can’t hear in that range.

早在2006年,冯和同事们就发现,这种不寻常的解剖结构使青蛙能够听到超声波,其中包括超过20千赫兹的频率。生物学家一直认为只有一些哺乳动物才有这种能力,例如蝙蝠、鲸鱼、海豚和一些啮齿动物才有这种能力。那个声波范围的声音我们听不到。

The streams that the frogs live in are quite noisy, but most of those sounds are low frequency. By restricting their vocalizations to the higher frequencies, including ultrasound, the frogs are better able to hear each other.

青蛙生活的溪流非常嘈杂,但这些声音大多是低频的。通过将它们的叫声限制在更高的频率,包括超声波,青蛙可以更好地听到彼此的声音。

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

“频率越高,信号被环境噪声干扰的程度就越小,或者至少被掩盖的程度就越小。”

In many animals, females prefer mating with larger males, usually because that's a sign of health and strength. And bigger males tend to produce lower frequency vocalizations. But with higher frequency calls being more effective in this habitat, Feng wondered if females might actually prefer smaller males.

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。体型较大的雄性倾向于发出较低频率的叫声。但是在这个栖息地,更高频率的叫声更有效,冯想知道雌性是否真的更喜欢较小的雄性。

Over the course of several nights, the researchers captured thirty-five pairs of frogs engaged in what biologists call amplexus. Which means while having sex. 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. Turns out, size really does matter.

在几个晚上的过程中,研究人员捕获了35对青蛙,生物学家称它们为amplexus。也就是做爱的时候。生物学家们测量了每只雄性蜘蛛的长度,也测量了附近那些不幸被捕获且没有发生性关系的雄性蜘蛛的长度。事实证明,规模真的很重要。

"The females are very unusual in that they really prefer smaller males over larger males."

“与体型较大的雄性相比,雌性更喜欢体型较小的雄性,这一点很不寻常。”

Next, the researchers brought the frogs into the lab. Each female was placed alongside two males. Here, too, females opted to mate with smaller-bodied males. And an analysis of the mating calls showed that the smaller males did use higher frequency sounds. The study was published in the Journal of Zoology.

接下来,研究人员把这些青蛙带进了实验室。每只雌性青蛙和两只雄性青蛙放在一起。在这里,雌性也选择与体型较小的雄性交配。一项对交配声音的分析表明,体型较小的雄性确实使用频率更高的声音。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. Over multiple generations you gradually develop these ultrasonic capabilities."

“我们认为雌性会优先选择体型较小的雄性,实际上我们可以看到这一趋势在几代人当中的延续……你可以看到这一特征的逐渐进化变化。”经过几代人的努力,你会逐渐发展出这种超声波能力。”

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

目前尚不清楚的是,雌性是通过视觉来判断雄性的体型,还是它们更容易听到雄性的高频叫声,从而更有可能与较小的雄性交配。这正是冯的团队正在进行的测试,他们在实验室里关灯向雌性萤火虫广播求偶的声音。

In the shadow of Huangshan Mountain in southeastern China lives a beige frog with black stripes. The concave-eared torrent frog, or Odorrana tormota, gets its name from its unusual hearing apparatus.

"It has kind of [an] ear canal-like structure like humans, and like most mammals. For most frog species, the eardrums are located on the body's surface, on the lateral part of the body surface. But here the eardrum is invisible because it is embedded deep inside the head, in the skull."

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

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. Biologists had always assumed that ability was restricted to some mammals because it was only known in bats, whales, dolphins, and some rodents. We can’t hear in that range.

The streams that the frogs live in are quite noisy, but most of those sounds are low frequency. By restricting their vocalizations to the higher frequencies, including ultrasound, the frogs are better able to hear each other.

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

In many animals, females prefer mating with larger males, usually because that's a sign of health and strength. And bigger males tend to produce lower frequency vocalizations. But with higher frequency calls being more effective in this habitat, Feng wondered if females might actually prefer smaller males.

Over the course of several nights, the researchers captured thirty-five pairs of frogs engaged in what biologists call amplexus. Which means while having sex. 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. Turns out, size really does matter.

"The females are very unusual in that they really prefer smaller males over larger males."

Next, the researchers brought the frogs into the lab. Each female was placed alongside two males. Here, too, females opted to mate with smaller-bodied males. And an analysis of the mating calls showed that the smaller males did use higher frequency sounds. The study was published in the Journal of Zoology.

"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. Over multiple generations you gradually develop these ultrasonic capabilities."

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


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