Data from: Reproductive isolation and introgression between sympatric Mimulus species|物种分化数据集|基因组学数据集

Incompletely isolated species provide an opportunity to investigate the
genetic mechanisms and evolutionary forces that maintain distinct species
in the face of ongoing gene flow. Here, we use field surveys and reduced
representation sequencing to characterize the patterns of reproductive
isolation, admixture and genomic divergence between populations of the
outcrossing wildflower Mimulus guttatus and selfing M. nasutus. Focusing
on a single site where these two species have come into secondary contact,
we find that phenological isolation is strong, although incomplete, and is
likely driven by divergence in response to photoperiod. In contrast to
previous field studies, which have suggested that F1-hybrid formation
might be rare, we discover patterns of genomic variation consistent with
ongoing introgression. Strikingly, admixed individuals vary continuously
from highly admixed to nearly pure M. guttatus, demonstrating ongoing
hybridization and asymmetric introgression from M. nasutus into M.
guttatus. Patterns of admixture and divergence across the genome show that
levels of introgression are more variable than expected by chance. Some
genomic regions show a reduced introgression, including one region that
overlaps a critical photoperiod QTL, whereas other regions show elevated
levels of interspecific gene flow. In addition, we observe a genome-wide
negative relationship between absolute divergence and the local
recombination rate, potentially indicating natural selection against M.
nasutus ancestry in M. guttatus genetic backgrounds. Together, our results
suggest that Mimulus speciation is both ongoing and dynamic and that a
combination of divergence in phenology and mating system, as well as
selection against interspecific alleles, likely maintains these sympatric
species.