@article {Ostevik767970, author = {Kate L Ostevik and Joanna L Rifkin and Hanhan Xia and Mark D Rausher}, title = {Asymmetric gene flow causes cascading reproductive isolation}, elocation-id = {767970}, year = {2019}, doi = {10.1101/767970}, publisher = {Cold Spring Harbor Laboratory}, abstract = {The interplay between hybridization and reproductive isolation is critical to the origin and maintenance of species. Hybridization between species is known to affect reproductive barrier strength. An extension of this relationship is the expectation that asymmetric hybridization and gene flow will have asymmetric effects on reproductive barrier strength. We tested this hypothesis in a pair of morning glory species which exhibit asymmetric gene flow in sympatry from highly selfing Ipomoea lacunosa into mixed mating I. cordatotriloba. Because of the direction of hybridization, we predicted that reproductive barrier strength would change to a greater extent in I. cordatotriloba than I. lacunosa. We tested this prediction by measuring the strength of a barrier to seed set between these species across their ranges. Consistent with our prediction, we found that sympatric I. cordatotriloba was more compatible with range-wide I. lacunosa than allopatric I. cordatotriloba, whereas sympatric and allopatric I. lacunosa were equally compatible with I. cordatotriloba. This difference likely reflects an asymmetric decrease in reproductive barriers in sympatric I. cordatotriloba. We further demonstrated that changes to sympatric I. cordatotriloba have decreased compatibility with allopatric populations. Thus, in a manner analogous to cascade reinforcement, introgression associated with asymmetric hybridization not only influences between-species isolation but also contributes to isolation within a species.}, URL = {https://www.biorxiv.org/content/early/2019/10/17/767970}, eprint = {https://www.biorxiv.org/content/early/2019/10/17/767970.full.pdf}, journal = {bioRxiv} }