Patterns of hybrid seed inviability in perennials of the Mimulus guttatus sp. complex reveal a potential role of parental conflict in reproductive isolation

Genomic conflicts may play a central role in the evolution of reproductive barriers. Theory predicts that early-onset hybrid inviability may stem from conflict between parents for resource allocation to offspring. Here we describe M. decorus; a group of cryptic species within the M. guttatus species complex that are largely reproductively isolated by hybrid seed inviability (HSI). HSI between M. guttatus and M. decorus is common and strong, but populations of M. decorus vary in the magnitude and directionality of HSI with M. guttatus. Patterns of HSI between M. guttatus and M. decorus, as well as within M. decorus conform to the predictions of parental conflict: firstly, reciprocal F1s exhibit size differences and parent-of-origin specific endosperm defects, secondly the extent of asymmetry between reciprocal F1 seed size is correlated with asymmetry in HSI, and lastly, inferred differences in the extent of conflict predict the extent of HSI between populations. We also find that HSI is...