Sharma Prashant P
Department of Zoology, University of Wisconsin-Madison, 352 Birge Hall, 430 Lincoln Drive, Madison, WI 53706, USA.
Integr Comp Biol. 2017 Sep 1;57(3):510-522. doi: 10.1093/icb/icx078.
The internal phylogeny of Chelicerata and the attendant evolutionary scenario of arachnid terrestrialization have a long and contentious history. Previous studies of developmental gene expression data have suggested that respiratory systems of spiders, crustaceans, and insects are all serially homologous structures derived from the epipods (outer appendage rami) of the arthropod ancestor, corresponding to an ancestral gill. A separate body of evidence has suggested that the respiratory systems of arachnids are modified, inverted telopods (inner rami, or legs). Here I review these dissonant homology statements and compare the developmental genetic basis for respiratory system development in insects and arachnids. I show that the respiratory primordia of arachnids are not positionally homologous to those of insects. I further demonstrate that candidate genes critical to tracheal fate specification in Drosophila melanogaster are expressed very differently in arachnid exemplars. Taken together, these data suggest that mechanisms of respiratory system development are not derived from homologous structures or mechanisms in insects and arachnids, and that different terrestrial arthropod lineages have solved the challenge of aerial respiration using different developmental mechanisms.
螯肢动物的内部系统发育以及蛛形纲动物向陆地演化的相关进化历程，有着漫长且充满争议的历史。先前对发育基因表达数据的研究表明，蜘蛛、甲壳类动物和昆虫的呼吸系统都是源自节肢动物祖先的上肢（外附肢分支）的系列同源结构，对应于祖先的鳃。另一组证据表明，蛛形纲动物的呼吸系统是经过改造的、倒置的端足（内分支，即腿）。在此，我回顾这些不一致的同源性观点，并比较昆虫和蛛形纲动物呼吸系统发育的发育遗传学基础。我发现蛛形纲动物的呼吸原基与昆虫的呼吸原基在位置上并非同源。我进一步证明，对黑腹果蝇气管命运特化至关重要的候选基因，在蛛形纲动物样本中的表达差异很大。综合这些数据表明，昆虫和蛛形纲动物呼吸系统的发育机制并非源自同源结构或机制，不同的陆地节肢动物谱系利用不同的发育机制解决了空气呼吸的挑战。
