Data from: Coalescent and biophysical models of stepping-stone gene flow in Neritid snails

Marine species in the Indo-Pacific have ranges that can span thousands of kilometers, yet studies increasingly suggest that mean larval dispersal distances are less than historically assumed. Gene flow across these ranges must therefore rely to some extent on larval dispersal among intermediate “stepping-stone” populations in combination with long-distance dispersal far beyond the mean of the dispersal kernel. We evaluate the strength of stepping-stone dynamics by employing a spatially explicit biophysical model of larval dispersal in the Tropical Pacific to construct hypotheses for dispersal pathways. We test these hypotheses with coalescent models of gene flow among high-island archipelagos in four Neritid gastropod species. Two of the species live in the marine intertidal, while the other two are amphidromous, living in freshwater but retaining pelagic dispersal. Dispersal pathways predicted by the biophysical model were strongly favored in 16 of 18 tests against alternate hypotheses. In regions where connectivity among high-island archipelagos was predicted as direct, there was no difference in gene flow between marine and amphidromous species. In regions where connectivity was predicted through stepping-stone atolls only accessible to marine species, gene flow estimates between high-island archipelagos were significantly higher in marine species. Moreover, one of the marine species showed a significant pattern of isolation-by-distance consistent with stepping-stone dynamics. While our results support stepping-stone dynamics in Indo-Pacific species, we also see evidence for non-equilibrium processes such as range expansions or rare long-distance dispersal events. This study provides an empirical assessment of a biophysical model that helps to shed light on larval dispersal pathways.

印度-太平洋（Indo-Pacific）海域的海洋物种分布范围可达数千公里，但越来越多的研究表明，平均幼虫扩散（larval dispersal）距离远低于此前的历史假设。因此，横跨这些分布范围的基因流（gene flow），在一定程度上必然依赖于中间“踏脚石种群（stepping-stone populations）”间的幼虫扩散，结合远超扩散核（dispersal kernel）均值的长距离扩散事件。本研究借助热带太平洋海域幼虫扩散的空间显式生物物理模型（spatially explicit biophysical model），评估踏脚石动态的强度，以此构建扩散通路假说。随后，针对4种蜑腹足类（Neritid gastropod）的高岛群岛种群间的基因流，采用溯祖模型（coalescent models）对上述假说进行检验。其中2个物种栖息于海洋潮间带，另外2个为两栖洄游（amphidromous）物种：成体生活于淡水，但保留浮游扩散能力。相较于备择假说，生物物理模型预测的扩散通路在18项检验中的16项得到了显著支持。在高岛群岛间被预测为直接连通的区域，潮间带海洋物种与两栖洄游物种的基因流并无显著差异；而在仅海洋物种可抵达的踏脚石环礁介导连通的区域，高岛群岛间的基因流在海洋物种中显著更高。此外，其中1种海洋物种呈现出与踏脚石动态相符的显著距离隔离（isolation-by-distance）格局。尽管本研究结果支持印度-太平洋物种的踏脚石动态，但同时也发现了非平衡过程的相关证据，例如种群扩张（range expansions）或罕见的长距离扩散事件。本研究对一款生物物理模型开展了实证评估，有助于阐明海洋幼虫的扩散通路机制。