A method for quantifying, visualising, and analysing gastropod shell form

Liew, T. S., & Schilthuizen, M. (2013). A method for quantifying, visualising, and analysing gastropod shell form (No. e157v1). PeerJ PrePrints. Supplementary materials Abstract Quantitative analysis of organismal form is an important component for almost every branch of biology. Although generally considered an easily-measurable structure, the quantification of gastropod shell form is still a challenge because shells lack homologous structures and have a spiral form that is difficult to capture with linear measurements. In view of this, we adopt the idea of theoretical modelling of shell form, in which the shell form is the product of aperture ontogeny profiles in terms of aperture growth trajectory that is quantified as curvature and torsion, and of aperture form that is represented by size and shape. We develop a workflow for the analysis of shell forms based on the aperture ontogeny profile, starting from the procedure of data preparation (retopologising the shell model), via data acquisition (calculation of aperture growth trajectory, aperture form and ontogeny axis), and data presentation (qualitative comparison between shell forms) and ending with data analysis (quantitative comparison between shell forms). We evaluate our methods on representative shells of the genus Opisthostoma, which exhibit great variability in shell form. The outcome suggests that our method is more robust, reproducible, and versatile than the conventional traditional and geometric morphometric approaches for the analysis of shell form. Finally, we propose several potential applications of our methods in functional morphology, theoretical modelling, taxonomy, and evolutionary biology.

Liew, T. S. 与 Schilthuizen, M. (2013). 一种量化、可视化与分析腹足类贝壳（gastropod shell）形态的方法（预印本编号e157v1）. PeerJ 预印本. 补充材料 摘要
生物体形态的定量分析是生物学几乎所有分支领域的重要组成部分。尽管腹足类贝壳通常被认为是一种易于测量的结构，但其形态的定量分析仍是一项挑战——这是因为贝壳缺乏同源结构，且其螺旋形态难以通过线性测量手段捕捉。有鉴于此，我们采用了贝壳形态理论建模的思路：贝壳形态由壳口个体发育轮廓（aperture ontogeny profiles）决定，具体体现为以曲率和扭转度量化的壳口生长轨迹（aperture growth trajectory），以及以大小和形态表征的壳口形态（aperture form）。我们基于壳口个体发育轮廓开发了一套贝壳形态分析工作流，该流程涵盖从数据预处理（重构贝壳模型拓扑结构）、数据获取（计算壳口生长轨迹、壳口形态与个体发育轴）、数据呈现（贝壳形态间的定性对比）到数据分析（贝壳形态间的定量对比）的完整环节。我们以壳口形态变异极为丰富的圆带螺属（Opisthostoma）代表性贝壳为对象，对所提方法进行了验证。研究结果表明，相较于传统方法与几何形态测量法（geometric morphometric approaches），我们的方法在贝壳形态分析中具备更强的鲁棒性、可重复性与通用性。最后，我们展望了该方法在功能形态学、理论建模、分类学与进化生物学领域的潜在应用场景。