Data from: Immigrant inviability produces a strong barrier to gene flow between parapatric ecotypes of Senecio lautus

Speciation proceeds when gene exchange is prevented between populations. Determining the different barriers preventing gene flow can therefore give insights into the factors driving and maintaining species boundaries. These reproductive barriers may result from intrinsic genetic incompatibilities between populations, from extrinsic environmental differences between populations, or a combination of both mechanisms. We investigated the potential barriers to gene exchange between three adjacent ecotypes of an Australian wildflower to determine the strength of individual barriers and the degree of overall isolation between populations. We found almost complete isolation between the three populations mainly due to premating extrinsic barriers. Intrinsic genetic barriers were weak and variable amongst populations. There were asymmetries in some intrinsic barriers due to the origin of cytoplasm in hybrids, which combined with weak selection against hybrids has the potential to facilitate gene flow in the system, specifically from Dune and Headland ecotypes into the Island ecotype. Overall, these results suggest that reproductive isolation between these three populations is almost complete despite the absence of geographic barriers, and that the main drivers of this isolation are ecologically based, consistent with the mechanisms underlying ecological speciation.

当种群间的基因交流被阻断时，物种形成过程便会启动。因此，解析阻断基因流的各类生殖障碍，能够为理解驱动并维持物种界限的核心因素提供启示。这类生殖屏障既可源于种群间的内在遗传不相容性，也可源于种群间的外在环境差异，或是两种机制共同作用的结果。我们以澳大利亚一种野生花卉的三个相邻生态型（ecotype）为研究对象，探究其种群间基因交流的潜在障碍，以明确各单一障碍的作用强度，以及种群间的整体隔离程度。研究发现，三个种群间几乎完全隔离，这一现象主要由交配前的外在障碍所致。内在遗传屏障的作用较弱，且在不同种群间存在差异。部分内在遗传屏障存在不对称性，这源于杂交个体的细胞质来源；这种不对称性与对杂交个体的弱选择压相结合，有可能促进该系统内的基因交流，具体表现为从沙丘（Dune）生态型、海岬（Headland）生态型向岛屿（Island）生态型的基因流动。综上，本研究结果表明：尽管不存在地理屏障，这三个种群间的生殖隔离已近乎完全；而该隔离的主要驱动因素源于生态分化，这与生态物种形成的底层机制相符。