塞舌尔岛有种青蛙用口腔听声音
文章来源:未知 文章作者:enread 发布时间:2013-09-03 06:37 字体: [ ]  进入论坛
(单词翻译:双击或拖选)
Gardiner's frogs from the Seychelles islands, one of the smallest frogs in the world, do not possess a middle ear with an eardrum(鼓膜,耳膜) yet can croak1(呱呱地叫) themselves, and hear other frogs. An international team of scientists using X-rays has now solved this mystery and established that these frogs are using their mouth cavity and tissue to transmit sound to their inner ears. The results are published in the Proceedings2 of the National Academy of Sciences on September 2, 2013.
 
The team led by Renaud Boistel from CNRS and University of Poitiers, comprised also scientists from Institut Langevin of ESPCI ParisTech, the Laboratoire de Mécanique et d'Acoustique in Marseilles, the Institute of Systems and Synthetic3 Biology at the University of Evry (France), the Nature Protection Trust of Seychelles, and the European Synchrotron ESRF in Grenoble.
 
The way sound is heard is common to many lineages of animals and appeared during the Triassic age (200-250 million years ago). Although the auditory systems of the four-legged animals have undergone many changes since, they have in common the middle ear with eardrum and ossicles, which emerged independently in the major lineages. On the other hand, some animals notably4 most frogs, do not possess an outer ear like humans, but a middle ear with an eardrum located directly on the surface of the head. Incoming sound waves make the eardrum vibrate, and the eardrum delivers these vibrations5 using the ossicles to the inner ear where hair cells translate them into electric signals sent to the brain. Is it possible to detect sound in the brain without a middle ear? The answer is no because 99.9% of a sound wave reaching an animal is reflected at the surface of its skin.
 
"However, we know of frog species that croak like other frogs but do no have tympanic middle ears to listen to each other. This seems to be a contradiction," says Renaud Boistel from the IPHEP of the University of Poitiers and CNRS. "These small animals, Gardiner's frogs, have been living isolated6 in the rainforest of the Seychelles for 47 to 65 million years, since these islands split away from the main continent. If they can hear, their auditory system must be a survivor7 of life forms on the ancient supercontinent Gondwana."
 
To establish whether these frogs actually use sound for communicate with each other, the scientists set up loudspeakers in their natural habitat and broadcast pre-recorded frog songs. This caused males present in the rainforest to answer, proving that they were able to hear the sound from the loudspeakers.
 
The next step was to identify the mechanism8 by which these seemingly deaf frogs were able to hear sound. Various mechanisms9 have been proposed: an extra-tympanic pathway through the lungs, muscles which in frogs connect the pectoral girdle to the region of the inner ear, or bone conduction. "Whether body tissue will transport sound or not depends on its biomechanical properties. With X-ray imaging techniques here at the ESRF, we could establish that neither the pulmonary system nor the muscles of these frogs contribute significantly to the transmission of sound to the inner ears," says Peter Cloetens, a scientist at the ESRF who took part in the study. "As these animals are tiny, just one centimetre long, we needed X-ray images of the soft tissue and the bony parts with micrometric resolution to determine which body parts contribute to sound propagation."
 
Numerical simulations helped to investigate the third hypothesis, that the sound was received through the frog's heads. These simulations confirmed that the mouth acts as a resonator, or amplifier, for the frequencies emitted by this species. Synchrotron X-ray imaging on different species showed that the transmission of the sound from the oral cavity to the inner ear has been optimized10 by two evolutionary11 adaptations: a reduced thickness of the tissue between the mouth and the inner ear and a smaller number of tissue layers between the mouth and the inner ear. "The combination of a mouth cavity and bone conduction allows Gardiner's frogs to perceive sound effectively without use of a tympanic middle ear," concludes Renaud Boistel.


点击收听单词发音收听单词发音  

1 croak yYLzJ     
vi.嘎嘎叫,发牢骚
参考例句:
  • Everyone seemed rather out of sorts and inclined to croak.每个人似乎都有点不对劲,想发发牢骚。
  • Frogs began to croak with the rainfall.蛙随着雨落开始哇哇叫。
2 proceedings Wk2zvX     
n.进程,过程,议程;诉讼(程序);公报
参考例句:
  • He was released on bail pending committal proceedings. 他交保获释正在候审。
  • to initiate legal proceedings against sb 对某人提起诉讼
3 synthetic zHtzY     
adj.合成的,人工的;综合的;n.人工制品
参考例句:
  • We felt the salesman's synthetic friendliness.我们感觉到那位销售员的虚情假意。
  • It's a synthetic diamond.这是人造钻石。
4 notably 1HEx9     
adv.值得注意地,显著地,尤其地,特别地
参考例句:
  • Many students were absent,notably the monitor.许多学生缺席,特别是连班长也没来。
  • A notably short,silver-haired man,he plays basketball with his staff several times a week.他个子明显较为矮小,一头银发,每周都会和他的员工一起打几次篮球。
5 vibrations d94a4ca3e6fa6302ae79121ffdf03b40     
n.摆动( vibration的名词复数 );震动;感受;(偏离平衡位置的)一次性往复振动
参考例句:
  • We could feel the vibrations from the trucks passing outside. 我们可以感到外面卡车经过时的颤动。
  • I am drawn to that girl; I get good vibrations from her. 我被那女孩吸引住了,她使我产生良好的感觉。 来自《简明英汉词典》
6 isolated bqmzTd     
adj.与世隔绝的
参考例句:
  • His bad behaviour was just an isolated incident. 他的不良行为只是个别事件。
  • Patients with the disease should be isolated. 这种病的患者应予以隔离。
7 survivor hrIw8     
n.生存者,残存者,幸存者
参考例句:
  • The sole survivor of the crash was an infant.这次撞车的惟一幸存者是一个婴儿。
  • There was only one survivor of the plane crash.这次飞机失事中只有一名幸存者。
8 mechanism zCWxr     
n.机械装置;机构,结构
参考例句:
  • The bones and muscles are parts of the mechanism of the body.骨骼和肌肉是人体的组成部件。
  • The mechanism of the machine is very complicated.这台机器的结构是非常复杂的。
9 mechanisms d0db71d70348ef1c49f05f59097917b8     
n.机械( mechanism的名词复数 );机械装置;[生物学] 机制;机械作用
参考例句:
  • The research will provide direct insight into molecular mechanisms. 这项研究将使人能够直接地了解分子的机理。 来自《简明英汉词典》
  • He explained how the two mechanisms worked. 他解释这两台机械装置是如何工作的。 来自《简明英汉词典》
10 optimized 81c61ac8ff2adb570ce4c7e7dfed59bd     
adj.最佳化的,(使)最优化的v.使最优化,使尽可能有效( optimize的过去式和过去分词 )
参考例句:
  • We are often asked whether consumer Web sites should be optimized for beginners or intermediates. 我们常常被问到这样的问题:消费类网站究竟应该为新手而优化,还是应该为中间用户而优化? 来自About Face 3交互设计精髓
  • GOOGLE Advertising optimized sequence, greatly increasing the advertising effect. 优化了GOOGLE广告位排列顺序,大大增加了广告效果。 来自互联网
11 evolutionary Ctqz7m     
adj.进化的;演化的,演变的;[生]进化论的
参考例句:
  • Life has its own evolutionary process.生命有其自身的进化过程。
  • These are fascinating questions to be resolved by the evolutionary studies of plants.这些十分吸引人的问题将在研究植物进化过程中得以解决。
TAG标签: mouth ear frogs
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