Data from: Fluctuating reproductive isolation and stable ancestry structure in a fine-scaled mosaic of hybridizing Mimulus monkeyflowers

Hybridization among taxa impacts a variety of evolutionary processes from
adaptation to extinction. We seek to understand both patterns of
hybridization across taxa and the evolutionary and ecological forces
driving those patterns. To this end, we use whole-genome low-coverage
sequencing of 458 wild-grown and 1565 offspring individuals to
characterize the structure, stability, and mating dynamics of admixed
populations of Mimulus guttatus and Mimulus nasutus across a decade of
sampling. In three streams, admixed genomes are common and a M. nasutus
organellar haplotype is fixed in M. guttatus, but new hybridization events
are rare. Admixture is strongly unidirectional, but each stream has a
unique distribution of ancestry proportions. In one stream, three distinct
cohorts of admixed ancestry are spatially structured at ~20-50m resolution
and stable across years. Mating system provides almost complete isolation
of M. nasutus from both M. guttatus and admixed cohorts, and is a partial
barrier between admixed and M. guttatus cohorts. Isolation due to
phenology is near-complete between M. guttatus and M. nasutus.
Phenological isolation is a strong barrier in some years between admixed
and M. guttatus cohorts, but a much weaker barrier in other years,
providing a potential bridge for gene flow. These fluctuations are
associated with differences in water availability across years, supporting
a role for climate in mediating the strength of reproductive isolation.
Together, mating system and phenology accurately predict fluctuations in
assortative mating across years, which we estimate directly using paired
maternal and offspring genotypes. Climate-driven fluctuations in
reproductive isolation may promote the longer-term stability of a complex
mosaic of hybrid ancestry, preventing either complete isolation or
complete collapse of species barriers.