Data for: Variation in reproductive isolation across a species range

<p>Reproductive isolation is often variable within species, a phenomenon that while largely ignored by speciation studies, can be leveraged to gain insight into the poten- tial mechanisms driving the evolution of genetic incompatibilities. We used experi- mental greenhouse crosses to characterize patterns of reproductive isolation among three divergent genetic lineages of Campanulastrum americanum that occur in close geographic proximity in the Appalachian Mountains. Substantial, asymmetrical repro- ductive isolation for survival due to cytonuclear incompatibility was found among the lineages (up to 94% reduction). Moderate reductions in pollen viability, as well as cytoplasmic male sterility, were also found between some Mountain populations. We then compared these results to previously established patterns of reproductive isola- tion between these Mountain lineages and a fourth, widespread Western lineage to fully characterize reproductive isolation across the complete geographic and genetic range of C. americanum. Reproductive isolation for survival and pollen viability was consistent across studies, indicating the evolution of the underlying genetic incompat- ibilities is primarily determined by intrinsic factors. In contrast, reproductive isolation for germination was only found when crossing Mountain populations with the Western lineage, suggesting the underlying genetic incompatibility is likely influenced by envi- ronmental or demographic differences between the two lineages. Cytoplasmic male sterility was also limited in occurrence, being restricted to a handful of Mountain pop- ulations in a narrow geographic range. These findings illustrate the complexity of spe- ciation by demonstrating multiple, independent genetic incompatibilities that lead to a mosaic of genetic divergence and reproductive isolation across a species range.</p>