Starck J Matthias, Mehnert Lisa, Biging Anja, Bjarsch Juliana, Franz-Guess Sandra, Kleeberger Daniel, Hörnig Marie
1Functional Morphology Group, Department of Biology 2, University of Munich (LMU), Biocenter Martinsried, Großhadernerstr. 2, D-82152 Planegg-, Martinsried, Germany.
Zoological Institute and Museum, Cytology and Evolutionary Biology, Soldmannstr 23, D17487 Greifswald, Germany.
Zoological Lett. 2018 Aug 4;4:20. doi: 10.1186/s40851-018-0104-0. eCollection 2018.
Ticks can survive long periods without feeding but, when feeding, ingest large quantities of blood, resulting in a more than 100-fold increase of body volume. We study morphological adaptations to changes in opisthosoma volume during feeding in the castor bean tick, . We aim to understand the functional morphological features that accommodate enormous changes in volume changes.
Using light and electron microscopy, we compare the cuticle and epidermis of the alloscutum, the epithelium of the midgut diverticula, and the tracheae of adult female ticks when fasting, semi-engorged, and fully engorged.
Our results add to an existing body of knowledge that the area of the epidermis increases by cellular differentiation, cellular hypertrophy, and changes in the shape of epithelial cells from pseudostratified to single layered prismatic in semi-engorged ticks, and to thin squamous epithelium in fully engorged ticks. We did not find evidence for cell proliferation. The midgut diverticula accommodate the volume increase by cellular hypertrophy and changes in cell shape. In fully engorged ticks, the epithelial cells of the midgut diverticula are stretched to an extremely thin, squamous epithelium. Changes in size and shape (and cell divisions) contribute to the accommodation of volume changes. Tracheae do not increase in size, but extend in length, thus following the volume changes of the opisthosoma in feeding ticks to secure oxygen supply to the internal organs.
Changes of epithelial tissue configuration in the epidermis and the midgut diverticula are described as important components of the morphological response to feeding in ticks. We provide evidence for a previously unknown mechanism hosted in the endocuticle of the tracheae that allows the tracheae of castor bean ticks to expand when the body volume increases and the distance between the respiratory spiracle and the oxygen demanding tissue enlarges. This is the first report of expandable tracheae in arthropods.
蜱虫在不进食的情况下可存活很长时间，但进食时会摄取大量血液，导致身体体积增加100多倍。我们研究蓖麻蜱进食过程中腹侧体体积变化的形态学适应。我们旨在了解适应体积巨大变化的功能形态特征。
使用光学显微镜和电子显微镜，我们比较了成年雌性蜱虫在禁食、半饱食和饱食状态下的背板角质层和表皮、中肠盲囊上皮以及气管。
我们的结果补充了现有知识，即表皮面积通过细胞分化、细胞肥大以及在半饱食蜱虫中上皮细胞从假复层变为单层棱柱形，在饱食蜱虫中变为薄鳞状上皮细胞而增加。我们没有发现细胞增殖的证据。中肠盲囊通过细胞肥大和细胞形状变化来适应体积增加。在饱食蜱虫中，中肠盲囊的上皮细胞被拉伸成极薄的鳞状上皮。大小和形状的变化（以及细胞分裂）有助于适应体积变化。气管大小不变，但长度增加，从而随着进食蜱虫腹侧体的体积变化来确保向内部器官供应氧气。
表皮和中肠盲囊中上皮组织构型的变化被描述为蜱虫进食形态学反应的重要组成部分。我们提供了证据，证明气管内膜中存在一种以前未知的机制，该机制使蓖麻蜱的气管在身体体积增加且呼吸气门与需氧组织之间的距离增大时能够扩张。这是节肢动物中可扩张气管的首次报道。
