Land colonization was a major event in the history of life. Among animals, insects exerted a staggering terrestrialization success, due to traits usually associated with post embryonic life stages, while the egg stage has been largely overlooked in comparative studies. In many insects, after blastoderm differentiation, the extraembryonic serosal tissue wraps the embryo and synthesizes the serosal cuticle, an extracellular matrix that lies beneath the eggshell and protects the egg against water loss. In contrast, in non-insect hexapods such as springtails (Collembola) the early blastodermal cells synthesize a blastodermal cuticle. Here, we investigate the relationship between blastodermal cuticle formation and egg resistance to desiccation in the springtails Orchesella cincta and Folsomia candida, two species with different oviposition environments and developmental rates. The blastodermal cuticle becomes externally visible in O. cincta and F. candida at 22 and 29% of embryogenesis, respectively. To contextualize, we describe the stages of springtail embryogenesis, exemplified by F. candida. Our physiological assays then showed that blastodermal cuticle formation coincides with an increase in egg viability in a dry environment, significantly contributing to hatching success. However, protection differs between species: while O. cincta eggs survive at least 2 hours outside a humid environment, the survival period recorded for F. candida eggs is only 15 minutes, which correlates with this species' requirement for humid microhabitats. We suggest that the formation of this cuticle protects the eggs, constituting an ancestral trait among hexapods that predated and facilitated the process of terrestrialization that occurred during insect evolution.

中文翻译：

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卵对跳虫干燥的抗性增加与胚泡表皮的形成有关：昆虫进化的生态进化意义

土地殖民化是生活史上的重大事件。在动物中，由于通常与胚胎后生命阶段有关的性状，昆虫发挥了惊人的地域还原作用，而在比较研究中，卵子阶段却被大大忽略了。在许多昆虫中，胚盘分化后，胚外浆膜组织包裹了胚并合成了浆膜角质层，浆膜角质层是一种位于卵壳下方的细胞外基质，可保护卵免受水分流失。相反，在非昆虫六足动物中，例如跳尾（Collembola），早期的胚泡表皮细胞合成胚盘表皮。在这里，我们调查了跳皮Orchesella cincta和念珠菌Folsomia candida中胚泡表皮形成与卵对脱水的抗性之间的关系，两种具有不同产卵环境和发育速度的物种。在胚乳和念珠菌中胚泡表皮分别在胚胎发生的22％和29％处可见。为了进行情境化，我们描述了跳蚤胚胎发生的各个阶段，例如念珠菌。然后，我们的生理学分析表明胚盘表皮的形成与干燥环境中卵生存力的增加相吻合，极大地促进了孵化的成功。但是，不同物种之间的保护有所不同：尽管O. cincta卵在潮湿环境下可以生存至少2小时，但念珠菌F. candida卵的生存期仅为15分钟，这与该物种对潮湿微生境的需求有关。我们建议这种表皮的形成可以保护卵，