Postmating reproductive isolation between species. Boxplots showing average seed set (a) and F1 viability (b) of crosses for various combinations of the three pairs of populations, respectively. Boxes and horizontal bars represent the central 50% and the median of the data, respectively. Dots represent outliers beyond 1.5 times the interquartile range. “N-N” and “R-R” represent crosses between individuals from the same population within Oryza nivara (N) and O. rufipogon (R), respectively. “N × N” and “R × R” represent crosses between individuals from different populations within the same species. “R × N” and “N × R” (dark columns) represent crosses between individuals from different species (with O. rufipogon as the maternal and paternal parents, respectively). Number of crosses for a specific combination is in parentheses.