Postcopulatory mate choice occurs ubiquitously in the animal kingdom. However, it is usually a major challenge to visualise the process taking place in a body. This fact makes it difficult to understand the mechanisms of the process. By focusing on the shape of female sperm storage organs (spermathecae), we aimed to elucidate their functional morphology using six representative beetle species and to simulate sperm dynamics in artificial spermathecae with different structural features. Morphology and material gradients were studied using micro-computed tomography (μCT) and confocal laser scanning microscopy. This study shows a diversity of external and internal structures of the spermathecae among species. Despite the diversity, all species possess a common pumping region, which is composed of a sclerotised chamber, muscles and a resilin-enriched region. By focusing on the species Agelastica alni, whose spermatheca is relatively simple in shape with an internal protuberance, we simulated sperm dynamics by establishing a fabrication method to create enlarged, transparent, flexible and low-cost 3D models of biological structures based on μCT data. This experiment shows that the internal protuberance in the species functions as an efficient mixing device of stored sperm. The observed spermathecal musculature implies that the sclerotised chamber of the spermatheca with muscles works as a pumping organ. Our fluid dynamics tests based on 3D printed spermathecae show that a tiny structural difference causes entirely different fluid dynamics in the spermatheca models. This result suggests that structural variations of the spermatheca strongly affect sperm dynamics. However, fluid dynamics tests still require essential measurements including sperm viscosity and the velocity of pumping cycles of the spermatheca.

中文翻译：

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3D打印的精子细胞作为实验模型，可了解叶甲虫的精子动力学

交配伴侣的选择普遍存在于动物界。然而，通常可视化在体内发生的过程是主要的挑战。这个事实使得很难理解该过程的机制。通过关注雌性精子存储器官（spermathecae）的形状，我们旨在使用六个有代表性的甲虫物种阐明其功能形态，并模拟具有不同结构特征的人工精子中的精子动力学。使用微计算机断层扫描（μCT）和共聚焦激光扫描显微镜对形态和材料梯度进行了研究。这项研究显示了不同物种之间精囊的外部和内部结构的多样性。尽管物种多样，但所有物种都拥有一个共同的抽水区域，该区域由一个硬化室组成，肌肉和富含弹性蛋白的区域。通过集中研究其精子形状相对简单，内部有突起的Agelastica alni物种，我们通过建立一种制造方法来模拟精子动力学，该方法可以基于μCT数据创建生物结构的扩大，透明，灵活和低成本的3D模型。该实验表明，物种中的内部突起可作为储存精子的有效混合装置。观察到的精囊肌肉组织暗示，具有肌肉的精囊的硬化室起着抽气器官的作用。我们基于3D打印的精囊的流体动力学测试表明，微小的结构差异会导致精囊模型的流体动力学完全不同。该结果表明，精子的结构变化强烈影响精子动力学。