Data from: Rapid divergence of mussel populations despite incomplete barriers to dispersal

Striking genetic structure among marine populations at small spatial scales is becoming evident with extensive molecular studies. Such observations suggest isolation at small scales may play an important role in forming patterns of genetic diversity within species. Isolation-by-distance, isolation-by-environment, and historical priority effects are umbrella terms for a suite of processes that underlie genetic structure, but their relative importance at different spatial and temporal scales remains elusive. Here, we use marine lakes in Indonesia to assess genetic structure and test relative roles of the processes in shaping genetic differentiation in populations of a bivalve mussel (Brachidontes sp.). Marine lakes are landlocked water bodies of similar age (6,000 – 10,000 years), but with heterogeneous environments and varying degrees of connection to the sea. Using a population genomic approach (double-digest Restriction-site Associated DNA sequencing), we show strong genetic structuring across populations (range FST: 0.07 – 0.24), and find limited gene flow through admixture plots. At large spatial scales (>1400km), a clear isolation-by-distance pattern was detected. At smaller spatial scales (<200km), this pattern is maintained, but accompanied by an association of genetic divergence with degree of connection. No signatures of isolation-by-environment were found. We hypothesize that (incomplete) dispersal barriers can cause initial isolation, allowing priority effects to give the numerical advantage necessary to initiate strong genetic structure. Priority effects may be strengthened by local adaptation, which our data potentially corroborates by showing a high correlation between mussel genotypes and temperature. Our study indicates an often-neglected role of evolution-mediated priority effects in shaping divergence.

随着大规模分子生物学研究的推进，小型空间尺度下海洋种群的显著遗传结构正逐渐被揭示。此类观测结果表明，小型尺度下的种群隔离可能在塑造物种种内遗传多样性格局中发挥重要作用。距离隔离（isolation-by-distance）、环境隔离（isolation-by-environment）以及历史优先效应（historical priority effects）是支撑遗传结构形成的一系列过程的统称，但其在不同空间与时间尺度下的相对重要性仍尚不明确。
本研究以印度尼西亚的海洋湖泊为研究对象，对一种双壳类贻贝（短齿蛤属，Brachidontes sp.）的种群遗传结构进行评估，并检验上述过程在塑造种群遗传分化中的相对作用。海洋湖泊为陆封型内陆水体，形成年代均为6000至10000年，但其环境存在异质性，且与海洋的连通程度各不相同。
本研究采用种群基因组学研究方法（double-digest Restriction-site Associated DNA sequencing），结果显示种群间存在显著的遗传结构，遗传分化系数（FST）的取值范围为0.07至0.24，且通过群体混合分析图谱发现种群间的基因交流十分有限。
在大空间尺度（>1400km）下，我们检测到了清晰的距离隔离模式；在小空间尺度（<200km）下，该模式依然存在，但同时伴随遗传分化与连通程度的显著关联。未发现环境隔离的相关信号。
我们提出假说：（不完全的）扩散障碍可引发初始种群隔离，使优先效应获得建立强遗传结构所需的数量优势。本地适应或可强化优先效应，本研究数据显示贻贝基因型与水温存在高度相关性，可为该假说提供佐证。
本研究揭示了进化介导的优先效应在塑造种群分化中常被忽视的重要作用。