CAUSE OF BIMODAL DISTRIBUTION IN THE SHAPE OF A TERRESTRIAL GASTROPOD
CAUSE OF BIMODAL DISTRIBUTION IN THE SHAPE OF A TERRESTRIAL GASTROPOD
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DOI：
10.1111/j.1558-5646.2009.00780.x
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发表时间：
2009-11-01
期刊：
影响因子：
3.3
通讯作者：
Chiba, Satoshi
中科院分区：
文献类型：
--
作者：
Okajima, Ryoko;Chiba, Satoshi
表型状态的分布通常是不连续和分散的。这种分布的一个例子可以在陆生腹足类的壳形状中找到，它们表现出双峰分布，即物种拥有高壳或平壳。在这里，我们提出了一个简单的模型来测试的假设，即双峰分布涉及到的最佳形状壳平衡的基板上。该模型通过力矩计算理论壳体平衡，并通过汇编已发表的数据并进行新的分析来获得壳体形状的经验分布。模型的解支持了假设的一部分，表明低螺旋壳是最好的平衡，更适合于在水平面上运动。此外，该模型表明，无论是高，低螺旋壳是很好的平衡，适合在垂直表面。螺旋指数（壳高除以直径）为1.4的壳是整体平衡最差的。因此，尖顶指数预计将显示双峰分布，谷值为1.4。这一预期得到了螺旋指数的经验分布的支持，这表明陆生腹足类壳形的双峰性与壳的平衡有关。
The distribution of a phenotypic state is often discontinuous and dispersed. An example of such a distribution can be found in the shell shapes of terrestrial gastropods, which exhibit a bimodal distribution whereby species possess either a tall shell or a flat shell. Here we propose a simple model to test the hypothesis that the bimodal distribution relates to the optimum shape for shell balance on the substrates. This model calculates the theoretical shell balance by moment and obtains empirical distribution of shell shape by compiling published data and performing a new analysis. The solution of the model supports one part of the hypothesis, showing that a low-spired shell is the best balanced and is better suited for locomotion on horizontal surface. Additionally, the model shows that both high- and low-spired shells are well balanced and suited on vertical surfaces. The shell with a spire index (shell height divided by diameter) of 1.4 is the least well balanced as a whole. Thus, spire index is expected to show a bimodal distribution with a valley at 1.4. This expectation was supported by empirical distribution of a spire index, suggesting that the bimodality of shell shape in terrestrial gastropods is related to shell balance.