A Snail Perspective on the Biogeography of Sulawesi, Indonesia: Origin and Intra-Island Dispersal of the Viviparous Freshwater Gastropod Tylomelania

The complex geological history of the Indonesian island Sulawesi has shaped the origin and subsequent diversification of its taxa. For the endemic freshwater snail Tylomelania a vicariant origin from the Australian margin has been hypothesized. Divergence time estimates from a mtDNA phylogeny based on a comprehensive island-wide sampling of Tylomelania fit regional tectonic constraints and support the ‘out-of-Australia’ vicariance hypothesis. The Banggai-Sula region of the Sula Spur, the Australian promontory colliding with West Sulawesi during the Miocene, is identified as a possible source area for the colonization of Sulawesi by the ancestor of Tylomelania. The molecular phylogeny also shows a rapid diversification of Tylomelania into eight major lineages with very little overlap in their distribution on the island. Haplotype networks provide further evidence for a strong spatial structure of genetic diversity in Tylomelania. Distribution boundaries of the major lineages do at best partially coincide with previously identified contact zones for other endemic species groups on Sulawesi. This pattern has likely been influenced by the poor dispersal capabilities and altitudinal distribution limits of this strict freshwater inhabitant. We suggest that late Miocene and Pliocene orogeny in large parts of Sulawesi has been the vicariant event driving primary diversification in Tylomelania.印度尼西亚苏拉威西岛复杂的地质历史，塑造了该岛境内生物类群的起源与后续分化过程。针对特有淡水螺属Tylomelania，学界曾提出其通过异域分化（vicariance）机制起源于澳大利亚陆缘的假说。基于全岛范围采样的Tylomelania线粒体DNA（mitochondrial DNA, mtDNA）系统发育树所得到的分化时间估算结果，与该区域的构造约束条件相符，且支持“源自澳大利亚”的异域分化假说。苏拉海脊（Sula Spur）的邦盖-苏拉区域——即中新世时期与苏拉威西西部碰撞的澳大利亚陆岬——被认定为Tylomelania祖先殖民苏拉威西岛的潜在起源地。该分子系统发育分析还显示，Tylomelania快速分化为8个主要支系，各支系在岛上的分布范围极少重叠。单倍型网络进一步证实，Tylomelania的遗传多样性存在显著的空间结构特征。这些主要支系的分布边界，至多仅能部分匹配此前在苏拉威西岛上发现的其他特有物种类群的接触带。这一分布格局很可能受到该专性淡水生物较弱的扩散能力与海拔分布限制的影响。我们认为，苏拉威西岛大部分区域在晚中新世至上新世期间发生的造山运动，正是驱动Tylomelania初始分化的异域分化事件。