Central Facility for Electron Microscopy, University of Ulm, Albert-Einstein-Allee 11, 89069 Ulm, Germany.
Bionics and Materials Development, Hamm-Lippstadt University of Applied Sciences, Marker Allee 76-78, 59063 Hamm, Germany; Department of Microstructure Physics and Alloy Design, Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-Str. 1, 40237 Düsseldorf, Germany.
J Struct Biol. 2020 Oct 1;212(1):107570. doi: 10.1016/j.jsb.2020.107570. Epub 2020 Jul 7.
To survive in its extreme habitat, the cuticle of the burrowing desert isopod Hemilepistus reaumuri requires properties distinct from isopods living in moist or mesic habitats. In particular, the anterior tergites are exposed to high mechanical loads and temperatures when individuals guard the entrance of their burrow. We have, therefore, investigated the architecture, composition, calcite texture and local mechanical properties of the tergite cuticle, with particular emphasis on large anterior cuticle tubercles and differences between the anterior and posterior tergite. Unexpectedly, structure and thickness of the epicuticle resemble those in mesic isopod species. The anterior tergite has a thicker endocuticle and a higher local stiffness than the posterior tergite. Calcite distribution in the cuticle is unusual, because in addition to the exocuticle the endocuticle distally also contains calcite. The calcite consists of a distal layer of dense and highly co-oriented crystal-units, followed proximally by irregularly distributed and, with respect to each other, misoriented calcite crystallites. The calcite layer at the tip of the tubercle is thicker relative to the tubercle slopes, and its crystallites are more misoriented to each other. A steep decrease of local stiffness and hardness is observed within a distal region of the cuticle, likely caused by a successive increase in the ACC/calcite ratio rather than changes in the degree of mineralisation. Comparison of the results with other isopods reveals a much lower ACC/calcite ratio in H. reaumuri and a correlation between the degree of terrestriality of isopod species and the magnesium content of the cuticle.
为了在其极端栖息地中生存，穴居沙漠等足目动物雷氏异尾虫的外骨骼需要具有不同于生活在潮湿或中等湿度生境中的等足目动物的特性。特别是，当个体守卫其洞穴入口时，前背板会暴露于高机械负荷和高温下。因此，我们研究了背板外骨骼的结构、组成、方解石纹理和局部力学性能，特别强调了大型前背板皮瘤和前背板与后背板之间的差异。出乎意料的是，外角质层的结构和厚度与中等湿度等足目物种相似。前背板的内角质层比后背板更厚，局部硬度也更高。方解石在表皮中的分布是不寻常的，因为除了外角质层外，内角质层在远端也含有方解石。方解石的分布在表皮中是不寻常的，因为除了外角质层外，内角质层在远端也含有方解石。方解石在表皮中的分布是不寻常的，因为除了外角质层外，内角质层在远端也含有方解石。方解石的分布在表皮中是不寻常的，因为除了外角质层外，内角质层在远端也含有方解石。方解石由一层致密且高度各向同性的晶体单元组成，近端则分布不规则，且相对于彼此，方解石晶体各向异性。皮瘤尖端的方解石层相对于皮瘤斜坡较厚，其晶体彼此之间的取向更为不规则。在表皮的远端区域观察到局部硬度和硬度急剧下降，这可能是由于 ACC/方解石比例的连续增加而不是矿化程度的变化所致。将结果与其他等足目动物进行比较表明，H. reaumuri 的 ACC/方解石比例要低得多，并且等足目动物的陆生程度与表皮中的镁含量之间存在相关性。
