Did internal transport, rather than directed locomotion, favor the evolution of bilateral symmetry in animals?
Did internal transport, rather than directed locomotion, favor the evolution of bilateral symmetry in animals?
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DOI：
10.1002/bies.20299
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发表时间：
2005-11-01
期刊：
影响因子：
4
通讯作者：
Finnerty, JR
中科院分区：
文献类型：
--
作者：
Finnerty, JR
对双侧对称起源的标准解释是，在定向运动中，双侧对称比径向对称更有优势。然而，最近的发育和系统发育研究表明，双侧对称可能在无根底栖动物中进化而来，早于定向运动的起源。另一种进化上可行的解释是，双侧对称的进化是为了通过影响肠道的区隔化和主要纤毛束的位置来提高内循环的效率。刺胞动物门的对称性从放射状到四放射状、双放射状和双侧均有不同，这一功能设计原则得到了最好的说明。在刺胞体中，两侧对称在内部解剖和纤毛束的分布中表现得最为明显。此外，双侧对称刺胞体通常是无柄的，在那些进行定向运动的双侧对称刺胞体中，次级体轴的方向与运动方向不一致，而双侧对称刺胞体通常是这样的。在刺胞体内部，可以通过实验分析和流体力学的计算机建模来验证双侧对称对内部循环的假设优势。通过对不同对称性物种间基因表达的比较研究，可以进一步探讨刺胞菌对称性的发育演化。(c) 2005 Wiley期刊有限公司
The standard explanation for the origin of bilateral symmetry is that it conferred an advantage over radial symmetry for directed locomotion. However, recent developmental and phylogenetic studies suggest that bilateral symmetry may have evolved in a sessile benthic animal, predating the origin of directed locomotion. An evolutionarily feasible alternative explanation is that bilateral symmetry evolved to improve the efficiency of internal circulation by affecting the compartmentalization of the gut and the location of major ciliary tracts. This functional design principle is illustrated best by the phylum Cnidaria where symmetry varies from radial to tetraradial, biradial and bilateral. In the Cnidaria, bilateral symmetry is manifest most strongly in the internal anatomy and the disposition of ciliary tracts. Furthermore, the bilaterally symmetrical Cnidaria are typically sessile and, in those bilaterally symmetrical cnidarians that undergo directed locomotion, the secondary body axis does not bear a consistent orientation to the direction of locomotion as it typically does in Bilateria. Within the Cnidaria, the hypothesized advantage of bilateral symmetry for internal circulation can be tested by experimental analysis and computer modeling of fluid mechanics. The developmental evolution of symmetry within the Cnidaria can be further explored through comparative gene expression studies among species whose symmetry varies. (c) 2005 Wiley Periodicals, Inc.