Complex brain and optic lobes in an early Cambrian arthropod
Complex brain and optic lobes in an early Cambrian arthropod
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DOI：
10.1038/nature11495
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发表时间：
2012-10-11
期刊：
影响因子：
64.8
通讯作者：
Strausfeld, Nicholas J.
中科院分区：
文献类型：
--
作者：
Ma, Xiaoya;Hou, Xianguang;Strausfeld, Nicholas J.
神经系统为理解主要节肢动物类群之间的进化关系提供了一个基本的数据来源（1,2）。节肢动物化石很少保存神经组织。因此，对寒武纪分类群的感觉和运动属性的推断一直局限于解释外部特征，如复眼(3)或感觉器官装饰附属物(4)，而早期分化的节肢动物很少在神经系统进化的背景下进行分析。在这里，我们报告了5.2亿年前的茎类节肢动物Fuxianhuia protensa的大脑和视叶的特殊保存，展示了寒武纪已知的最令人信服的神经解剖学。抚仙徽亚的前大脑由视神经叶提供，这证明了三个嵌套的视神经中心服务于前视眼的痕迹。来自单侧触角的神经定义了下脑，一对粗壮的尾端神经表明了连续的三脑成分。阜县慧虫与现存的Malacostraca和insect有共同的三孔前脑和巢状视神经球（2,6），这表明这些特征在一些最早的节肢动物中存在。Fuxianhuia的大脑影响了一些分子分析，这些分析认为六足动物的祖先是类枝足动物（7,8），六足动物和头足动物可能是六足动物的姐妹类群（9,10）。关于鳃足类动物的简单大脑是否接近于祖先昆虫的大脑，或者它是否是二次简化的结果，直到现在，由于缺乏化石证据，解决争论一直受到阻碍。富仙辉亚的复杂脑符合神经特征的分支分析，表明鳃足类动物起源于类似马拉孔甲类动物的祖先，但经历了六足类动物和马拉孔甲类动物共同的脑中心的进化减少和特征逆转(2)。复杂大脑的早期起源可能是多种视觉行为的驱动因素，这一观点与寒武纪早期的复眼相一致，后者在大小和分辨率上与现代昆虫和malacostracans的复眼相当(3)。
The nervous system provides a fundamental source of data for understanding the evolutionary relationships between major arthropod groups(1,2). Fossil arthropods rarely preserve neural tissue. As a result, inferring sensory and motor attributes of Cambrian taxa has been limited to interpreting external features, such as compound eyes(3) or sensilla decorating appendages(4), and early-diverging arthropods have scarcely been analysed in the context of nervous system evolution. Here we report exceptional preservation of the brain and optic lobes of a stem-group arthropod from 520 million years ago (Myr ago), Fuxianhuia protensa(5), exhibiting the most compelling neuroanatomy known from the Cambrian. The protocerebrum of Fuxianhuia is supplied by optic lobes evidencing traces of three nested optic centres serving forward-viewing eyes. Nerves from uniramous antennae define the deutocerebrum, and a stout pair of more caudal nerves indicates a contiguous tritocerebral component. Fuxianhuia shares a tripartite pre-stomodeal brain and nested optic neuropils with extant Malacostraca and Insecta(2,6), demonstrating that these characters were present in some of the earliest derived arthropods. The brain of Fuxianhuia impacts molecular analyses that advocate either a branchiopod-like ancestor of Hexapoda(7,8) or remipedes and possibly cephalocarids as sister groups of Hexapoda(9,10). Resolving arguments about whether the simple brain of a branchiopod approximates an ancestral insect brain or whether it is the result of secondary simplification has until now been hindered by lack of fossil evidence. The complex brain of Fuxianhuia accords with cladistic analyses on the basis of neural characters, suggesting that Branchiopoda derive from a malacostracan-like ancestor but underwent evolutionary reduction and character reversal of brain centres that are common to hexapods and malacostracans(2). The early origin of sophisticated brains provides a probable driver for versatile visual behaviours, a view that accords with compound eyes from the early Cambrian that were, in size and resolution, equal to those of modern insects and malacostracans(3).