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.