PDF(Pubmed)
Abstract：
All animals evolved from a single lineage of unicellular precursors more than 600 million years ago. Thus, the biological and genetic foundations for animal sensation, cognition and behavior must necessarily have arisen by modifications of pre-existing features in their unicellular ancestors. Given that the single-celled ancestors of the animal kingdom are extinct, the only way to reconstruct how these features evolved is by comparing the biology and genomic content of extant animals to their closest living relatives. Here, we reconstruct the Umwelt (the subjective, perceptive world) inhabited by choanoflagellates, a group of unicellular (or facultatively multicellular) aquatic microeukaryotes that are the closest living relatives of animals. Although behavioral research on choanoflagellates remains patchy, existing evidence shows that they are capable of chemosensation, photosensation and mechanosensation. These processes often involve specialized sensorimotor cellular appendages (cilia, microvilli, and/or filopodia) that resemble those that underlie perception in most animal sensory cells. Furthermore, comparative genomics predicts an extensive \"sensory molecular toolkit\" in choanoflagellates, which both provides a potential basis for known behaviors and suggests the existence of a largely undescribed behavioral complexity that presents exciting avenues for future research. Finally, we discuss how facultative multicellularity in choanoflagellates might help us understand how evolution displaced the locus of decision-making from a single cell to a collective, and how a new space of behavioral complexity might have become accessible in the process.
摘要：
所有动物都是从6亿年前的单细胞前体的单一谱系进化而来的。因此，动物感觉的生物学和遗传基础，认知和行为必然是由其单细胞祖先中预先存在的特征的修改而产生的。鉴于动物界的单细胞祖先已经灭绝，重建这些特征是如何进化的唯一方法是将现存动物的生物学和基因组内容与其最近的近亲进行比较。这里,我们重建了Umwelt(主观的，感知世界）居住着鞭毛虫，一组单细胞（或兼性多细胞）水生微真核生物，是动物的近亲。尽管对鞭毛虫的行为研究仍然不完整，现有证据表明它们具有化学感觉，光感觉和机械感觉。这些过程通常涉及专门的感觉运动细胞附件（纤毛，微绒毛,和/或丝状伪足）类似于大多数动物感觉细胞中感知的基础。此外，比较基因组学预测了一种广泛的“感官分子工具包”，这两者都为已知行为提供了潜在的基础，并表明存在一个很大程度上未描述的行为复杂性，为未来的研究提供了令人兴奋的途径。最后,我们讨论了鞭毛虫中的兼性多细胞性如何帮助我们理解进化如何将决策的轨迹从单个细胞转移到集体，以及在这个过程中一个新的行为复杂性空间是如何变得可访问的。
