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 rapidly evolving, as populations that exhibit the most HSI are each others’ closest relative. Lastly, while all populations are largely outcrossing, we find that the differences in the inferred strength of conflict scale positively with p, suggesting that demographic or life history factors may influence the rate of parental conflict driven evolution. Overall, these patterns suggest the rapid evolution of parent-of-origin specific resource allocation alleles coincident with HSI within and between M. guttatus and M. decorus. Parental conflict may therefore be an important evolutionary driver of reproductive isolation.

This submission contains 2 data files:

1) Patterns_of_HSI_Mdecorus_guttatus.xlsx

Patterns of hybrid seed inviability, germination and seed size for crosses between 19 populations of M. decorus and 1-5 populations of M. guttatus. Column names: Mat= maternal genotype, Pat= paternal genotype, rep= plate replicate for germination assay, cross.type=interspecific or intraspecific cross- D= M. decorus, G=M. guttatus, maternal parent is listed first. dec.clade=genetic lineage of M. decorus, total.germ= total number of seeds germinated (out of 20), percent.germ=the percentage of seeds germinated, average germ=average germination across replicate plates for that specific cross.

2) Patterns_of_HSI_WithinMdecorus.xlsx

Patterns of hybrid seed inviability and seed size for crosses between all populations of M. decorus and 2 focal populations: one from the northern diploid clade (IMP), and one from the southern diploid clade (Odell Creek). Column names: Mat= maternal genotype, Mat.Rep= maternal plant replicate for that popultion, Pat= paternal genotype, Pat.Rep= paternal plant replicate for that popultion, cross.type= the type of cross performed, maternal parent is listed first (codes are as follows: P=4x decorus, S=southern decorus, N=northern decorus, O=Odell Creek- 'southern focal individual')), clade= is the cross between southern M. decorus or involving tetraploids ("South" or "4x", respectively), total seeds= total seeds produced, viable looking= number of seeds that appear viable, inviable looking= number of seeds appearing inviable, prop.viable= proportion viable seeds produced.

Missing data have been replaced with "NA".