Data from: Sexual dimorphism in shells of Cochlostoma septemspirale (Caenogastropoda, Cyclophoroidea, Diplommatinidae, Cochlostomatinae)

Sexual dimorphisms in shell-bearing snails expressed by characteristic traits of their respective shells would offer the possibility for a lot of studies about gender distribution in populations, species, etc. In this study, the seven main shell characters of the snail Cochlostoma septemspirale were measured in both sexes: (1) height and (2) width of the shell, (3) height and (4) width of the aperture, (5) width of the last whorl, (6) rib density on the last whorl, and (7) intensity of the reddish or brown pigments forming three bands over the shell. The variation of size and shape was explored with statistical methods adapted to principal components analysis (PCA) and linear discriminant analysis (LDA). In particular, we applied some multivariate morphometric tools for the analysis of ratios that have been developed only recently, that is, the PCA ratio spectrum, allometry ratio spectrum, and LDA ratio extractor. The overall separation of the two sexes was tested with LDA cross validation. The results show that there is a sexual dimorphism in the size and shape of shells. Females are more slender than males and are characterised by larger size, a slightly reduced aperture height but larger shell height and whorl width. Therefore they have a considerable larger shell volume (about one fifth) in the part above the aperture. Furthermore, the last whorl of females is slightly less strongly pigmented and mean rib density slightly higher. All characters overlap quite considerably between sexes. However, by using cross validation based on the 5 continuous shell characters more than 90% of the shells can be correctly assigned to each sex.

具壳蜗牛的壳体特征性状所体现的性别二态性，可为种群、物种等层面的性别分布研究提供诸多契机。本研究针对七旋螺（Cochlostoma septemspirale）的两性个体，测定了7项主要壳体性状：(1)壳体高度、(2)壳体宽度；(3)壳口高度、(4)壳口宽度；(5)末螺层宽度；(6)末螺层肋纹密度；(7)壳体上形成三条色带的红褐色或棕色色素强度。本研究采用适配于主成分分析（PCA）与线性判别分析（LDA）的统计学方法，探究了壳体大小与形状的变异规律；尤为特别的是，还运用了近年开发的比率分析多元形态计量工具，即PCA比率谱、异速生长比率谱与LDA比率提取器。通过LDA交叉验证，对两性的整体区分效果进行了检验。研究结果表明，壳体的大小与形状存在性别二态性：雌性个体较雄性更为修长，体型更大，壳口高度略低，但壳体高度与螺层宽度更大；因此，壳口上方的壳体体积较雄性高出约五分之一，增幅显著。此外，雌性个体的末螺层色素沉着程度略低，而平均肋纹密度略高。不过，所有性状在两性间均存在较为显著的重叠。但借助基于5个连续壳体性状的交叉验证，可将超过90%的个体正确归类至对应性别。