三叶虫头部的模块化与假设的眼睛节段起源一致,Evolution and Development

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三叶虫头部的模块化与假设的眼睛节段起源一致
Evolution and Development ( IF 2.6 ) Pub Date : 2022-09-16 , DOI: 10.1111/ede.12418
Ernesto E Vargas-Parra ₁ , Melanie J Hopkins ₁

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三叶虫头部具有多种功能，由几个融合的部分组成。然而，三叶虫头部的基本组织，以及模式是否在三叶虫中是保守的，仍然不清楚。将头部建模为由不同的模块或子单元组成，因此有可能半独立地进化，可以揭示潜在的组织模式。使用几何形态计量学评估了基于节肢动物比较发育生物学的模块化组织假设。从两种奥陶纪三叶虫物种Calyptaulax annulata (Phacopida) 和Cloacaspis senilis的头盖骨中收集的二维（半）地标数据集(Olenida sensu Adrain, 2011) 进行了分析。使用协方差比 (CR) 评估模块化的程度和模式，将假定模块内的协变与它们之间的协变进行比较，并使用源自 CR 的效应大小度量来比较不同模型的拟合度。当将眼睛视为一个独特的模块时，为C. annulata确定的最佳模块假设显示眼睛和头部的最前部区域集成为一个模块。C. senilis的最佳模块化假设更复杂，但眼睛仍然主要与头部的前部强烈共变。后者也适用于这两个物种的所有其他得到充分支持的模型。这些结果可以解释为对应于早期节肢动物最前眼部的发育信号，该信号在整个发育过程中保留，尽管可能存在与功能需求相关的选择压力。

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Modularity in the trilobite head consistent with the hypothesized segmental origin of the eyes

The trilobite head served multiple functions and was composed of several fused segments. Yet, the underlying organization of the trilobite head, and whether patterns are conserved across trilobites, remains unclear. Modeling the head as being composed of modules, or subunits that vary and thus have the potential to evolve semi-independently can reveal underlying patterns of organization. Hypotheses of modular organization based on the comparative developmental biology of arthropods were evaluated using geometric morphometrics. Two-dimensional (semi)landmark datasets collected from the cranidia of two Ordovician trilobite species, Calyptaulax annulata (Phacopida) and Cloacaspis senilis (Olenida sensu Adrain, 2011) were analyzed. The degree and pattern of modularity were assessed using the covariance ratio (CR), which compares the covariation within putative modules to the covariation between them, and the fit of different models was compared using an effect size measure derived from the CR. When treating the eyes as a distinct module, the best modular hypothesis identified for C. annulata shows the eyes and anteriormost region of the head integrated as a single module. The best modular hypotheses for C. senilis are more complex but the eyes still covary mostly strongly with the anterior part of the head. The latter is also the case for all other well-supported models for both species. These results can be interpreted as a developmental signal corresponding to the anteriormost ocular segment of early arthropods that is retained throughout development, despite any likely selective pressures related to functional needs.

更新日期：2022-09-16

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