Integrative microscopy to explore physical and nanomechanical properties of eggshells of diapausing embryos in Rotifera: a proof-of-concept study
Integrative microscopy to explore physical and nanomechanical properties of eggshells of diapausing embryos in Rotifera: a proof-of-concept study
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DOI：
10.1080/00222933.2023.2279255
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发表时间：
2023-12
影响因子：
0.8
通讯作者：
Stephanie Meyer;T. Q. Araújo;E. J. Walsh;R. Wallace;Rick Hochberg
中科院分区：
文献类型：
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作者：
Stephanie Meyer;T. Q. Araújo;E. J. Walsh;R. Wallace;Rick Hochberg
摘要 无脊椎动物的滞育胚胎代表着对未来种群的投资。因此，它们必须能够承受各种环境攻击。因此，它们的蛋壳应该能够抵抗捕食者、沉积物的伤害，或者干燥时的过度收缩。迄今为止，还没有对大多数产生滞育卵的无脊椎动物的蛋壳进行直接的纳米力学测量。在这里，我们使用三种方法来了解两种轮虫（一种淡水物种（萼花轮虫）和一种咸水物种（B. plicatilis））的蛋壳如何耐受恶劣条件：（1）原子力显微镜测量弹性和硬度； (2) 透射电子显微镜研究超微结构； (3)扫描电子显微镜检查表面特征。我们将这些值与丰年虾（Artemia salina）包囊和蚊子（埃及伊蚊）越冬卵的测量值进行了比较。我们的结果表明，轮虫蛋壳结构相似，并且具有相当的纳米力学值。虽然轮虫蛋壳的杨氏模量（约 13–16 MPa）和硬度值（1.84–1.85 × 10−2 GPa）低于卤虫和伊蚊的蛋壳，但所有物种的蛋壳都相对有弹性，并且不太耐变形。形成卵库（即丰年虫、臂尾轮虫）的贝壳的柔韧性可能是为了抵抗与埋藏在沉积物中相关的物理力作用下的破裂。尽管轮虫蛋壳的蛋壳厚度、超微结构、装饰或纳米力学值之间没有明显的关系，但我们假设蛋壳成分可能在决定弹性和硬度方面发挥重要作用。未来的研究应该考虑采用综合方法来了解蛋壳结构、化学和力学在保护滞育胚胎方面的重要性。
ABSTRACT Diapausing embryos of invertebrates represent investments in future populations. Thus, they must be capable of withstanding a variety of environmental assaults. Consequently, their eggshells should be adapted to resist injuries from predators, sediments, or excessive shrinkage if desiccated. To date, there have been no direct nanomechanical measurements of the eggshells of most invertebrates that produce diapausing eggs. Here, we used three approaches to understand how the eggshells of two rotifers, a freshwater species (Brachionus calyciflorus) and a brackish-water species (B. plicatilis), tolerate harsh conditions: (1) atomic force microscopy to measure elasticity and hardness; (2) transmission electron microscopy to study ultrastructure; (3) scanning electron microscopy to examine surface features. We compared these values to measurements of brine shrimp (Artemia salina) cysts and mosquito (Aedes aegypti) overwintering eggs. Our results revealed that rotifer eggshells are structurally similar and have comparable nanomechanical values. While rotifer eggshells had lower Young’s moduli (ca 13–16 MPa) and hardness values (1.84–1.85 × 10−2 GPa) than eggshells of Artemia and Aedes, eggshells of all species were relatively elastic and not particularly resistant to deformation. Pliancy of shells that form egg banks (ie Artemia, Brachionus) may be an adaptation to resist cracking under the physical forces associated with burial in sediments. Although there are no obvious relationships among eggshell thickness, ultrastructure, ornamentation, or nanomechanical values in rotifer eggshells, we hypothesise that eggshell composition may play an important role in determining elasticity and hardness. Future studies should consider an integrative approach to understand the importance of eggshell structure, chemistry, and mechanics in protecting diapausing embryos.