Data from: Genetic structure and shell shape variation within a rocky shore whelk suggests both diverging and constraining selection with gene flow

Variation in snail shell shape has provided evolutionary biologists with excellent material for the study of local adaptation to local environments. However, assuming shell shape variation is evidence of distinct lineages (species) may have led to taxonomic inflation within some gastropod lineages. Here we compare shell shape variation and genetic structure of two independent lineages of New Zealand rocky shore whelks in order to understand the process that lead to an unusual disjunct distribution. We examined the Buccinulum vittatum complex (three subspecies plus B. colensoi) using mitochondrial DNA sequences, 849 single nucleotide polymorphisms, and geometric morphometric data on shell shape. Specimens within the range of Buccinulum colensoi shared nuclear markers and mtDNA haplotypes with the southern subspecies B. vittatum littorinoides, while the northern samples (B. v. vittatum) had distinct genotypes. We infer that gene flow between B. colensoi and B. v. littorinoides is greater than between either of these taxa and B. v. vittatum. The distinctive shell sculpturing of B. colensoi is maintained despite gene flow, suggesting a role for selection. Although the shell form of B. colensoi appears to be an adaptation to local conditions we did not observe convergent evolution in the sympatric whelk species Cominella maculosa.

蜗牛壳形变异为进化生物学家开展物种对本地环境的局部适应研究提供了优质实验材料。然而，若直接将壳形变异作为不同演化支（物种）存在的依据，可能会引发部分腹足类（gastropod）演化支内的分类学膨胀问题。本研究针对新西兰岩岸蛾螺的两个独立演化支展开壳形变异与遗传结构对比分析，以解析造就该类群异常间断分布格局的演化机制。我们以带纹蛾螺复合群（Buccinulum vittatum complex，含3个亚种及Colensoi蛾螺（Buccinulum colensoi））为研究对象，采用线粒体DNA（mitochondrial DNA）序列、849个单核苷酸多态性（single nucleotide polymorphisms）位点以及壳形几何形态测量学数据开展系统性分析。分布于Colensoi蛾螺分布范围内的标本，其核基因标记与线粒体DNA单倍型（mtDNA haplotypes）均与南部亚种带纹蛾螺岩岸亚种（B. v. littorinoides）一致，而北部样本（B. v. vittatum）则具有独特的基因型。我们推断，Colensoi蛾螺与带纹蛾螺岩岸亚种之间的基因流强度，高于二者分别与带纹蛾螺vittatum亚种之间的基因流。尽管存在基因流，Colensoi蛾螺独特的壳面雕刻特征仍得以维持，这提示自然选择在其中发挥了作用。虽然Colensoi蛾螺的壳形看似是对本地环境的适应性特征，但我们并未在同域分布的蛾螺物种斑点蛾螺（Cominella maculosa）中观测到趋同演化现象。