Comparative sea spider neuroanatomy: exploring neural characters to illuminate phylogeny and evolution of an old arthropod lineage with limited morphological disparity

该项目旨在比较海洋拟海蜘蛛(海蜘蛛)的主要分类群(“科”)的成体神经解剖学，并示范研究这种节肢动物谱系中的成体神经发生。作为所有其他海龟的姊妹类，在试图阐明海龟神经系统的进化时，海龟是一个关键的分类群。现存的比目鱼的身体组织非常均匀，特征是头部区域有三对专门的附肢，躯干有四对行走的腿。然而，虽然行走的腿的结构是严格保守的，但“头”附肢显示出明显的分类群特有的变异。然而，到目前为止，无论是外部形态，还是分子序列数据，都没有使碧龙科系统发育的强大重建成为可能，使得对内部解剖的仔细检查变得迟迟不能进行。由于已有文献证明神经特征在主要节肢动物谱系水平上的系统发育推断中是有用的，因此碧龙类中枢神经系统(CNS)是一种很有前途的内部器官系统。使用现代技术(包括通过免疫标记各种神经活性物质和随后的高分辨率成像，对细胞上的中枢神经系统结构进行三维重建将为细胞水平的研究提供基础。此外，体内细胞增殖实验结合基因表达研究和神经元回填将典型地探索成体神经发生过程-这一未被研究的现象可能是许多节肢动物特定中枢神经系统区域可塑性的基础。该项目将产生第一个关于甲鱼纲内部器官系统的数据矩阵，涵盖所有现存的科。分支分析将(1)测试超细胞和细胞水平的神经特征在这个形态差异有限的古老节肢动物谱系中的实用性，(2)阐明神经和外部形态特征之间的潜在冲突，特别是在结构可变的“头”与保守的躯干之间，以及(3)允许对碧龙科的分子系统发育进行关键评估。此外，将重建碧龙骨底纹的神经解剖学特征。通过与其他主要节肢动物谱系的比较，这将为海龟和节肢动物神经系统的进化提供信息。在其他方面，它希望揭示更多的仿形--甚至在分子上--仍然不能令人满意地支持的单叶植物(真螺旋藻)。

This project aims to compare adult neuroanatomy across the major taxa (“families”) of the marine Pycnogonida (sea spiders), as well as to exemplarily study adult neurogenesis in this arthropod lineage. As likely sister group to all other chelicerates, pycnogonids are a pivotal taxon to consider, when trying to elucidate chelicerate nervous system evolution. Extant pycnogonids show a remarkably uniform body organization, featuring the “head” region with three specialized appendage pairs and the trunk with four walking leg pairs. However, while the walking leg structure is strictly conserved, the “head” appendages show drastic taxon-specific variations. Yet, neither external morphology, nor molecular sequence data have hitherto enabled robust reconstruction of pycnogonid phylogeny, rendering scrutiny of internal anatomy overdue. Owing to the documented usefulness of neural characters for phylogenetic inference at the level of major arthropod lineages, the pycnogonid central nervous system (CNS) is a promising internal organ system to begin with. Using modern-day techniques (incl. micro-CT) 3D-reconstruction of supracellular CNS structures will provide the backbone for studies at the cell level via immunolabeling of various neuroactive substances and subsequent high-resolution imaging. Additionally, in-vivo cell proliferation experiments coupled with gene expression studies and neuronal backfills will exemplarily explore adult neurogenic processes – an understudied phenomenon that may underlie plasticity of specific CNS areas in many arthropod taxa. The project will result in the first data matrix for an internal organ system of Pycnogonida, covering all extant families. Cladistic analyses will (1) test the utility of supracellular and cell-level neural characters in this old arthropod lineage with limited morphological disparity, (2) illuminate potential conflicts between neural and external morphological characters, especially in the structurally variable “head” versus the conserved trunk, and (3) allow critical evaluation of molecular pycnogonid phylogenies. Further, neuroanatomical features of the pycnogonid ground pattern will be reconstructed. Via comparison to other major arthropod lineages, this will inform on chelicerate and arthropod nervous system evolution. Among others, it is hoped to reveal additional apomorphies of the – even molecularly – still unsatisfactorily supported monophylum (Pycnogonida + Euchelicerata).