How Does Life Adapt to a Gravitational Environment? The Outline of the Terrestrial Gastropod Shell

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 ( ) and outline (cylindricality) is theoretically estimated. When the shell grows i...

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Bibliographic Details
Published in:The American naturalist 2011-12, Vol.178 (6), p.801-809
Main Authors: Okajima, Ryoko, Chiba, Satoshi
Format: Article
Language:English
Subjects:
Adaptation, Physiological
Animal and plant ecology
Animal behavior
Animal Shells - anatomy & histology
Animal Shells - growth & development
Animal Shells - physiology
Animal, plant and microbial ecology
Animals
Biological and medical sciences
Biological Evolution
Center of gravity
Curvature
Cylindrical shells
Diameters
Environment
Fresh water
Frustums
Fundamental and applied biological sciences. Psychology
Gastropoda
Gastropoda - anatomy & histology
Gastropoda - growth & development
Gastropoda - physiology
General aspects
Geometric shapes
Geometry
Gravitation
Gravity
Invertebrates
Land
Locomotion
Modeling
Models, Biological
Mollusca
Mollusks
Snails
Terrestrial ecosystems
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Summary: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 ( ) 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.
ISSN:0003-0147
1537-5323
DOI:10.1086/662674