From egg to "no-body": an overview and revision of developmental pathways in the ancient arthropod lineage Pycnogonida.
From egg to "no-body": an overview and revision of developmental pathways in the ancient arthropod lineage Pycnogonida.
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DOI：
10.1186/s12983-017-0192-2
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发表时间：
2017
影响因子：
2.8
通讯作者：
Krapp F
中科院分区：
文献类型：
--
作者：
Brenneis G;Bogomolova EV;Arango CP;Krapp F
节肢动物的多样性在动物王国中是无与伦比的。个体发育的研究对于理解节肢动物令人难以置信的形态差异背后的发育过程至关重要，从而最终揭示导致其成功的进化转变。对实验室模式生物的研究已经获得了有关节肢动物众多发育机制的深入数据。然而，尽管自比较进化发育生物学（evo-devo）出现以来，研究的分类单元的范围显着增加，但几个较小的类群仍然没有得到充分研究。其中包括奇异的Pycnogonida（海蜘蛛）或“无人”，这是一种在解释节肢动物发育和进化方面占据重要系统发育地位的分类单元。 Pycnogonid 的发育在科和属水平上是可变的，有时甚至同属物种也表现出不同的发育模式。在这里，我们总结了 19 世纪末以来的可用数据。我们澄清和解决了重生殖文献中持续存在的术语问题，并根据（1）孵化阶段的类型、（2）胚胎后发育过程中的发育形态特征和（3）选定的生活史特征区分了五种发育途径。基于系统发育分析和化石记录，我们讨论了重生殖器发育的合理的拟形特征，以便与其他节肢动物进行比较。这些特征包括（1）具有相等大小的卵裂球的全胚性、不规则卵裂，（2）由单个瓶状细胞启动原肠胚形成，（3）胚胎发生过程中缺乏形态上不同的胚带，（4）孵化阶段的寄生自由生活的原羽幼虫，以及（5）幼体后期和幼体阶段的半变形发育。此外，我们提出了冠群 Pycnogonida 内的进化发展轨迹。在过去的几十年里，对重生殖器胚胎后发育的研究的复兴提供了各种新的见解。然而，现代胚胎数据的稀缺性——包括基因表达和功能研究的实际缺乏——需要在未来的研究中得到解决，以加强与进化-发育框架内的其他节肢动物和节肢动物外群的比较。我们的综述可以作为此类研究目标物种的知情选择的基础，这不仅将揭示螯合物的发育和进化，而且有可能为节肢动物祖先的变形发育提供重要的见解。
Arthropod diversity is unparalleled in the animal kingdom. The study of ontogeny is pivotal to understand which developmental processes underlie the incredible morphological disparity of arthropods and thus to eventually unravel evolutionary transformations leading to their success. Work on laboratory model organisms has yielded in-depth data on numerous developmental mechanisms in arthropods. Yet, although the range of studied taxa has increased noticeably since the advent of comparative evolutionary developmental biology (evo-devo), several smaller groups remain understudied. This includes the bizarre Pycnogonida (sea spiders) or “no-bodies”, a taxon occupying a crucial phylogenetic position for the interpretation of arthropod development and evolution. Pycnogonid development is variable at familial and generic levels and sometimes even congeneric species exhibit different developmental modes. Here, we summarize the available data since the late 19th century. We clarify and resolve terminological issues persisting in the pycnogonid literature and distinguish five developmental pathways, based on (1) type of the hatching stage, (2) developmental-morphological features during postembryonic development and (3) selected life history characteristics. Based on phylogenetic analyses and the fossil record, we discuss plausible plesiomorphic features of pycnogonid development that allow comparison to other arthropods. These features include (1) a holoblastic, irregular cleavage with equal-sized blastomeres, (2) initiation of gastrulation by a single bottle-shaped cell, (3) the lack of a morphologically distinct germ band during embryogenesis, (4) a parasitic free-living protonymphon larva as hatching stage and (5) a hemianamorphic development during the postlarval and juvenile phases. Further, we propose evolutionary developmental trajectories within crown-group Pycnogonida. A resurgence of studies on pycnogonid postembryonic development has provided various new insights in the last decades. However, the scarcity of modern-day embryonic data – including the virtual lack of gene expression and functional studies – needs to be addressed in future investigations to strengthen comparisons to other arthropods and arthropod outgroups in the framework of evo-devo. Our review may serve as a basis for an informed choice of target species for such studies, which will not only shed light on chelicerate development and evolution but furthermore hold the potential to contribute important insights into the anamorphic development of the arthropod ancestor.