Organization for the Strategic Coordination of Research and Intellectual Property, Meiji University, 1-1-1 Higashimita, Tamaku, Kawasaki 214-8571, Japan.
Am Nat. 2011 Dec;178(6):801-9. doi: 10.1086/662674. Epub 2011 Oct 20.
How do several characteristics adapt to gravity while mutually influencing each other? Our study addresses this issue by focusing on the terrestrial gastropod shell. The geometric relationship between the spire index (shell height/diameter) and outline (cylindricality) is theoretically estimated. When the shell grows isometrically, a high-spired shell becomes conical in shape and a low-spired shell becomes cylindrical in shape. A physical model shows that the lowest- and highest-spired shells are the most balanced. In addition, a cone shape is the most balanced for a low-spired shell, and a column shape is the most balanced for a high-spired shell. Spire index and cylindricality measured for freshwater gastropods follow the relationship estimated by the model, whereas those for terrestrial gastropods deviate from this relationship. This translates to a high shell being more cylindrical than a flat shell, except in the case of extremely high or low shells. This suggests that the shape of the most balanced shells (lowest and highest shell heights) is constrained by coiling geometry but that relatively unbalanced shells (intermediate shell heights) do not follow a coiling geometry, as a result of adaptation to enable the snail to carry its shell more effectively.
几种特征如何在相互影响的同时适应重力？我们的研究通过关注陆地腹足纲贝壳来解决这个问题。理论上估计了壳高/直径的螺层指数（spire index）与轮廓（圆柱度）之间的几何关系。当贝壳等比例生长时，高螺层的贝壳会变成圆锥形，低螺层的贝壳会变成圆柱形。物理模型表明，最低和最高螺层的贝壳最为平衡。此外，对于低螺层的贝壳，锥形最为平衡，对于高螺层的贝壳，柱状最为平衡。淡水腹足纲动物的螺层指数和圆柱度符合模型估计的关系，而陆地腹足纲动物则偏离了这种关系。这意味着高壳比扁壳更接近圆柱形，除了非常高或非常低的壳。这表明，最平衡的贝壳（最低和最高壳高）的形状受到卷绕几何形状的限制，但相对不平衡的贝壳（中间壳高）不会遵循卷绕几何形状，这是为了适应使蜗牛更有效地携带贝壳。
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