Dangles O, Pierre D, Magal C, Vannier F, Casas J
Université de Tours, IRBI UMR CNRS 6035, Parc Grandmont, 37200 Tours, France.
J Exp Biol. 2006 Nov;209(Pt 21):4363-70. doi: 10.1242/jeb.02485.
Juvenile crickets suffer high rates of mortality by natural predators that they can detect using extremely sensitive air-sensing filiform hairs located on their cerci. Although a huge amount of knowledge has accumulated on the physiology, the neurobiology and the biomechanics of this sensory system in adults, the morphological and functional aspects of air sensing have not been as well studied in earlier life history stages. Using scanning electronic microscopy, we performed a survey of all cercal filiform hairs in seven instars of the wood cricket (Nemobius sylvestris). Statistical analyses allowed us to quantify profound changes in the number, the length and the distribution of cercal hairs during development. Of particular importance, we found a fivefold increase in hair number and the development of a bimodal length-frequency distribution of cercal hairs from the second instar onwards. Based on theoretical estimations of filiform hair population coding, we found that the cercal system is functional for a wide range of frequencies of biologically relevant oscillatory flows, even from the first instar. As the cricket develops, the overall sensitivity of the cercal system increases as a result of the appearance of new hairs, but the value of the best tuned frequency remains fixed between 150 and 180 Hz after the second instar. These frequencies nicely match those emitted by natural flying predators, suggesting that the development of the cercal array of hairs may have evolved in response to such signals.
幼年蟋蟀很容易成为天敌的猎物，它们能利用位于尾须上极其敏感的气敏丝状毛来探测天敌。尽管关于成年蟋蟀这一感觉系统的生理学、神经生物学和生物力学已经积累了大量知识，但在其早期生命阶段，气敏的形态学和功能方面尚未得到充分研究。我们使用扫描电子显微镜对木蟋蟀（Nemobius sylvestris）七龄若虫的所有尾须丝状毛进行了调查。统计分析使我们能够量化发育过程中尾须毛在数量、长度和分布上的显著变化。特别重要的是，我们发现从二龄若虫开始，尾须毛的数量增加了五倍，并且出现了双峰长度频率分布。基于丝状毛群体编码的理论估计，我们发现即使从一龄若虫开始，尾须系统对于广泛的生物相关振荡流频率都是有功能的。随着蟋蟀的发育，由于新毛的出现，尾须系统的整体敏感性增加，但在二龄若虫之后，最佳调谐频率的值保持在150至180赫兹之间不变。这些频率与天然飞行天敌发出的频率非常匹配，这表明尾须毛阵列的发育可能是为了响应此类信号而进化的。
