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.RIdataData set including the strength of Reproductive barriers to gene exchange between 3 populations of Senecio lautus. Includes Parental (pure crosses) and F1 Hybrid