Martín-Vega Daniel, Simonsen Thomas J, Hall Martin J R
Department of Life Sciences, Natural History Museum, London, SW7 5BD, United Kingdom.
Naturhistorisk Museum Aarhus, Aarhus C, DK-8000, Denmark.
J Morphol. 2017 May;278(5):629-651. doi: 10.1002/jmor.20660. Epub 2017 Feb 9.
Metamorphosis of cyclorrhaphous flies takes place inside a barrel-like puparium, formed by the shrinking, hardening and darkening of the third-instar larval cuticle. The opacity of this structure hampers the visualization of the morphological changes occurring inside and therefore a full understanding of the metamorphosis process. Here, we use micro-computed tomography (micro-CT) to describe the internal morphological changes that occur during metamorphosis of the blow fly, Calliphora vicina Robineau-Desvoidy 1830 (Diptera: Calliphoridae) at a greater temporal resolution than anything hitherto published. The morphological changes were documented at 10% intervals of the total intra-puparial period, and down to 2.5% intervals during the first 20% interval, when the most dramatic morphological changes occur. Moreover, the development of an internal gas bubble, which plays an essential role during early metamorphosis, was further investigated with X-ray images and micro-CT virtual sections. The origin of this gas bubble has been largely unknown, but micro-CT virtual sections show that it is connected to one of the main tracheal trunks. Micro-CT virtual sections also provided enough resolution for determining the completion of the larval-pupal and pupal-adult apolyses, thus enabling an accurate timing of the different intra-puparial life stages. The prepupal, pupal, and pharate adult stages last for 7.5%, 22.5%, and 70% of the total intra-puparial development, respectively. Furthermore, we provide for the first time quantitative data on the development of two organ systems of the blow fly: the alimentary canal and the indirect flight muscles. There is a significant and negative correlation between the volume of the indirect flight muscles and the pre-helicoidal region of the midgut during metamorphosis. The latter occupies a large portion of the thorax during the pupal stage but narrows progressively as the indirect flight muscles increase in volume during the development of the pharate adult.
环裂蝇类的变态发生在一个桶状的蛹壳内，蛹壳由三龄幼虫表皮收缩、硬化和变黑形成。这种结构的不透明性阻碍了对内部发生的形态变化的观察，因此妨碍了对变态过程的全面理解。在此，我们使用微计算机断层扫描（micro-CT）以比迄今发表的任何研究更高的时间分辨率描述了红头丽蝇（Calliphora vicina Robineau-Desvoidy 1830，双翅目：丽蝇科）变态过程中发生的内部形态变化。在蛹内总发育时期的10%间隔记录形态变化，在最初20%间隔内形态变化最剧烈时，记录间隔缩小到2.5%。此外，利用X射线图像和micro-CT虚拟切片进一步研究了在变态早期起重要作用的一个内部气泡的发育情况。这个气泡的起源在很大程度上尚不清楚，但micro-CT虚拟切片显示它与一条主要气管干线相连。Micro-CT虚拟切片还提供了足够的分辨率来确定幼虫-蛹和蛹-成虫蜕皮的完成情况，从而能够准确确定蛹内不同生命阶段的时间。预蛹期、蛹期和蛹后期分别持续蛹内总发育时间的7.5%、22.5%和70%。此外，我们首次提供了关于红头丽蝇两个器官系统发育的定量数据：消化道和间接飞行肌。在变态过程中，间接飞行肌的体积与中肠的螺旋前区域之间存在显著的负相关。后者在蛹期占据胸部的很大一部分，但随着蛹后期间接飞行肌体积的增加，它会逐渐变窄。
