A bridge between original and novel states: ontogeny and function of “suction discs” in the Branchiura (Crustacea)
A bridge between original and novel states: ontogeny and function of “suction discs” in the Branchiura (Crustacea)
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DOI：
10.1111/j.1525-142x.2011.00462.x
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发表时间：
2011-03
影响因子：
2.9
通讯作者：
Tomonari Kaji;O. Møller;Akira Tsukagoshi
中科院分区：
文献类型：
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作者：
Tomonari Kaji;O. Møller;Akira Tsukagoshi
在进化过程中新结构的出现面临着一个解释问题，留下了与祖先结构难以弥合的差距。这种困难是由于缺乏中间阶段造成的。鳃虫是一种外寄生甲壳类动物，它们使用一对“吸盘”附着在宿主身上。这些结构被修改第一上颌骨。在个体发育过程中，第一上颌骨从正常的头侧附属器转变为专门的吸盘。然而，据推测，祖先鳃类缺乏吸盘在成人和第一上颌骨仍然是一个正常的附属物。我们描述了肌肉的安排，在发展中的第一上颌骨在Argulus coregoni。吸盘起源于第一和第二豆荚的融合。吸盘的吸盘肌与早期幼虫插入第二足节的肌肉同源。吸盘的发展过程可以看作是进化过程的“重演”。因此，我们展示了第一上颌骨如何在新结构的进化过程中不仅保持生物学作用，而且保持功能连续性。从这个例子中可以明显看出，如果个体发生中出现了新新奇的中间阶段，那么它至少可以帮助解决一些新结构的神秘现象。
SUMMARY The emergence of novel structures in the course of evolution faces an explanatory problem, leaving the gap from the ancestral structures difficult to bridge. This difficulty is caused by the lack of intermediate stages. Branchiurans are ectoparasitic crustaceans which use a pair of “suction discs” to attach to their host. These structures are modified first maxillae. During ontogeny, the first maxillae transform from a normal cephalic appendage to the specialized suction disc. However, supposedly ancestral branchiurans lack the suction discs in the adults and the first maxilla remains a normal appendage throughout. We describe the muscular arrangements in the developing first maxillae in Argulus coregoni. The suction discs originate as a fusion of the first and second podomeres. The sucker muscles of the suction discs are homologous to the muscles that insert in the second podomere at the early larval stages. The developmental process of the suction disc can be seen as a “recapitulation” of the evolutionary process. We thus show how the first maxilla can maintain not just the biological role but also a functional continuity during the evolution of the novel structure. From this example it is obvious that the intermediate stages of the emerging novelty, if present in the ontogeny, can help solve at least some of the enigmatic appearances of novel structures.