Data from: Long-term stasis and short-term divergence in the phenotypes of microsnails on oceanic islands

Phenotypic divergence is often unrelated to genotypic divergence. An extreme example is rapid phenotypic differentiation despite genetic similarity. Another extreme is morphological stasis despite substantial genetic divergence. These opposite patterns have been viewed as reflecting opposite properties of the lineages. In this study, phenotypic radiation accompanied by both rapid divergence and long-term conservatism is documented in the inferred molecular phylogeny of the micro land snails Cavernacmella (Assimineidae) on the Ogasawara Islands. The populations of Cavernacmella on the Sekimon limestone outcrop of Hahajima Island showed marked divergence in shell morphology. Within this area, one lineage diversified into types with elongated turret shells, conical shells and flat disc-like shells without substantial genetic differentiation. Additionally, a co-occurring species with these types developed a much larger shell size. Moreover, a lineage adapted to live inside caves in this area. In contrast, populations in the other areas exhibited no morphological differences despite high genetic divergence among populations. Accordingly, the phenotypic evolution of Cavernacmella in Ogasawara is characterized by a pattern of long-term stasis and periodic bursts of change. This pattern suggests that even lineages with phenotypic conservatism could shift to an alternative state allowing rapid phenotypic divergence.表型分化（Phenotypic divergence）往往与基因型分化（genotypic divergence）并无关联。一类极端特例为遗传相似度极高却发生快速表型分化；另一极端情形则是尽管存在显著的遗传分化，物种却维持形态停滞（morphological stasis）。这两类对立的模式曾被认为反映了不同支系（lineage）的固有属性差异。本研究通过对小笠原群岛（Ogasawara Islands）上小型陆地蜗牛洞穴螺属（Cavernacmella，盖螺科（Assimineidae））的推断分子系统发育树（molecular phylogeny）进行分析，记录了伴随快速分化与长期保守性的表型辐射（phenotypic radiation）现象。母岛（Hahajima Island）濑见门石灰岩露头处的洞穴螺属种群，其贝壳形态（shell morphology）出现了显著分化。在该区域内，一个支系（lineage）分化出长塔形螺壳、锥形螺壳和平盘状螺壳等多种类型，却未发生显著的遗传分化。此外，与这些壳型共存的另一个物种，其螺壳体型显著增大。不仅如此，该区域内还有一个支系（lineage）适应了洞穴生境。与之形成鲜明对比的是，其他区域的种群尽管彼此间存在高度遗传分化，却未表现出任何形态差异。由此可见，小笠原群岛洞穴螺属的表型演化呈现出长期停滞与周期性爆发式变化交替的特征。该模式表明，即便原本维持表型保守性（phenotypic conservatism）的支系（lineage），也可能转变为可快速发生表型分化的状态。