Background In tunicates, the capacity to build an adult body via non-embryonic development (NED), i.e., asexual budding and whole body regeneration, has been gained or lost several times across the whole subphylum. A recent phylogeny of the family Styelidae revealed an independent acquisition of NED in the colonial species Polyandrocarpa zorritensis and highlighted a novel budding mode. In this paper, we provide the first detailed characterization of the asexual life cycle of P. zorritensis. Results Bud formation occurs along a tubular protrusion of the adult epidermis, the stolon, in a vascularized area defined as budding nest. The bud arises through a folding of the epithelia of the stolon with the contribution of undifferentiated mesenchymal cells. This previously unreported mode of bud onset leads to the formation of a double vesicle, which starts to develop into a zooid through morphogenetic mechanisms common to other Styelidae. The budding nest can also continue to accumulate nutrients and develop into a round-shaped structure, designated as spherule, which represents a dormant form able to survive low temperatures. Conclusions To understand the mechanisms of NED and their evolution, it is fundamental to start from a robust phylogenetic framework in order to select relevant species to compare. The anatomical description of P. zorritensis NED provides the foundation for future comparative studies on plasticity of budding and regeneration in tunicates.

中文翻译：

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Polyandrocarpa zorritensis 的新出芽模式：无性发育和全身再生比较研究的模型。

背景 在被囊动物中，通过非胚胎发育 (NED) 即无性出芽和全身再生来构建成体的能力在整个亚门中已经获得或失去了数次。Styelidae 家族最近的系统发育揭示了在殖民地物种 Polyandrocarpa zorritensis 中独立获得 NED，并突出了一种新的萌芽模式。在本文中，我们首次详细描述了 P. zorritensis 的无性生命周期。结果芽的形成沿着成年表皮的管状突起，匍匐茎，在被定义为芽巢的血管化区域发生。芽通过匍匐茎上皮的折叠而产生，其中未分化的间充质细胞的贡献。这种以前未报道的芽开始模式导致形成双囊泡，它开始通过其他 Styelidae 常见的形态发生机制发展成动物。萌芽巢穴还可以继续积累养分，发育成圆形结构，称为小球，代表一种能够在低温下生存的休眠形态。结论 要了解 NED 的机制及其进化，必须从稳健的系统发育框架开始，以选择相关物种进行比较。P. zorritensis NED 的解剖学描述为未来对被囊动物出芽和再生可塑性的比较研究提供了基础。它代表一种能够在低温下存活的休眠形式。结论 要了解 NED 的机制及其进化，必须从稳健的系统发育框架开始，以选择相关物种进行比较。P. zorritensis NED 的解剖学描述为未来对被囊动物出芽和再生可塑性的比较研究提供了基础。它代表一种能够在低温下存活的休眠形式。结论 要了解 NED 的机制及其进化，必须从稳健的系统发育框架开始，以选择相关物种进行比较。P. zorritensis NED 的解剖学描述为未来对被囊动物出芽和再生可塑性的比较研究提供了基础。