背景:呼吸器官的获取是动物陆地化的关键创新之一。陆地等足动物,甲壳类动物谱系,可以成为研究呼吸器官进化的有趣模型,因为他们根据栖息地展示了各种各样的呼吸结构。然而,这些结构的进化过程和起源尚不清楚,由于缺乏有关其发展过程的信息。为了了解发展机制,我们比较了三种等足物种形成不同呼吸结构的发育过程,即,在Nagurusocinawaensis(Trachelipodidae)中,\'背侧呼吸场\'在变形虫(变形虫科),and虫中没有呼吸结构的腹足类动物参见。椭圆(雷管科)。
结果:在未覆盖肺的冲绳奈斯,在曼加后幼年期,近端血淋巴窦周围的上皮和角质层发育成呼吸结构。另一方面,在Al。有背侧呼吸场的巴西,未来呼吸结构的区域已经存在于曼卡1期,孵化后立即,发生腹侧上皮外侧突出的地方,形成呼吸结构。此外,在Ar中的腹足类动物。cf.椭圆,在胚胎后发育过程中,只有增厚的背侧角质层和近端血淋巴窦发育,没有特殊的形态发生。
结论:这项研究表明,陆生等足类动物的呼吸结构主要通过胚胎后上皮修饰发展,但是在未覆盖的肺和背侧呼吸区域之间,上皮发育成呼吸结构的位置有所不同。这表明这两种类型的呼吸结构不是由发育程度的简单差异引起的。未来对分子发育机制的分析将有助于确定这些是异位变化的结果还是具有不同的进化起源。总的来说,本研究为等足类呼吸器官的进化发育研究提供了基础信息。
BACKGROUND: The acquisition of air-breathing organs is one of the key innovations for terrestrialization in animals. Terrestrial isopods, a crustacean lineage, can be interesting models to study the evolution of respiratory organs, as they exhibit varieties of air-breathing structures according to their habitats. However, the evolutionary processes and origins of these structures are unclear, due to the lack of information about their developmental processes. To understand the developmental mechanisms, we compared the developmental processes forming different respiratory structures in three isopod species, i.e., \'uncovered lungs\' in Nagurus okinawaensis (Trachelipodidae), \'dorsal respiratory fields\' in Alloniscus balssi (Alloniscidae), and pleopods without respiratory structures in Armadilloniscus cf. ellipticus (Detonidae).
RESULTS: In N. okinawaensis with uncovered lungs, epithelium and cuticle around the proximal hemolymph sinus developed into respiratory structures at post-manca juvenile stages. On the other hand, in Al. balssi with dorsal respiratory fields, the region for the future respiratory structure was already present at manca 1 stage, immediately after hatching, where the lateral protrusion of ventral epithelium occurred, forming the respiratory structure. Furthermore, on pleopods in Ar. cf. ellipticus, only thickened dorsal cuticle and the proximal hemolymph sinus developed during postembryonic development without special morphogenesis.
CONCLUSIONS: This study shows that the respiratory structures in terrestrial isopods develop primarily by postembryonic epithelial modifications, but the epithelial positions developing into respiratory structures differ between uncovered lungs and dorsal respiratory fields. This suggests that these two types of respiratory structures do not result from simple differences in the degree of development. Future analysis of molecular developmental mechanisms will help determine whether these are the result of heterotopic changes or have different evolutionary origins. Overall, this study provides fundamental information for evolutionary developmental studies of isopod respiratory organs.