Neuhofer Daniela, Wohlgemuth Sandra, Stumpner Andreas, Ronacher Bernhard
Department of Biology, Humboldt Universität zu Berlin, Berlin, Germany.
Proc Biol Sci. 2008 Sep 7;275(1646):1965-74. doi: 10.1098/rspb.2008.0527.
We investigated encoding properties of identified auditory interneurons in two not closely related grasshopper species (Acrididae). The neurons can be homologized on the basis of their similar morphologies and physiologies. As test stimuli, we used the species-specific stridulation signals of Chorthippus biguttulus, which evidently are not relevant for the other species, Locusta migratoria. We recorded spike trains produced in response to these signals from several neuron types at the first levels of the auditory pathway in both species. Using a spike train metric to quantify differences between neuronal responses, we found a high similarity in the responses of homologous neurons: interspecific differences between the responses of homologous neurons in the two species were not significantly larger than intraspecific differences (between several specimens of a neuron in one species). These results suggest that the elements of the thoracic auditory pathway have been strongly conserved during the evolutionary divergence of these species. According to the 'efficient coding' hypothesis, an adaptation of the thoracic auditory pathway to the specific needs of acoustic communication could be expected. We conclude that there must have been stabilizing selective forces at work that conserved coding characteristics and prevented such an adaptation.
我们研究了两种亲缘关系不紧密的蝗虫（蝗科）中已识别的听觉中间神经元的编码特性。这些神经元基于其相似的形态和生理特征可被认为是同源的。作为测试刺激，我们使用了大垫尖翅蝗的物种特异性摩擦发声信号，显然这些信号与另一种蝗虫——飞蝗无关。我们记录了这两个物种听觉通路第一级中几种神经元类型对这些信号产生的脉冲序列。使用一种脉冲序列指标来量化神经元反应之间的差异，我们发现同源神经元的反应具有高度相似性：两个物种中同源神经元反应的种间差异并不显著大于种内差异（同一物种中一个神经元的几个标本之间）。这些结果表明，在这些物种的进化分歧过程中，胸部听觉通路的元件得到了强烈的保留。根据“高效编码”假说，可以预期胸部听觉通路会适应声学通讯的特定需求。我们得出结论，一定存在起稳定作用的选择力，这些选择力保留了编码特征并阻止了这种适应。
