Data from: The genetic architecture of quantitative variation in the self-incompatibility response within Phlox drummondii (Polemoniaceae)

Flowering plants display extensive variation in selfing rate, a trait with
significant ecological and evolutionary consequences. Many species use
genetic mechanisms to recognize and reject self-pollen (termed
self-incompatibility or SI), and the loss of SI is one of the most common
evolutionary transitions among flowering plants. Despite the ubiquity of
transitions to self-compatibility (SC), little is known about the genetic
architecture through which SC evolves. Specifically, it is important to
determine if SC has a polygenic or simple genetic basis and if variation
in compatibility localizes to the genomic locus causing self-pollen
recognition (the “S-locus”). Phlox drummondii (Polemoniaceae) has been a
model system for exploring mating system evolution and expresses extensive
range-wide variation in the SI response. Here we investigate the genetic
architecture of SC variants segregating within this otherwise SI species.
Using multiple independent crosses, we uncover numerous QTLs associated
with intraspecific variation in SI, consistent with a polygenic genetic
architecture. While some QTLs overlap across mapping experiments, other
QTLs are unique, suggesting that multiple genetic routes to SC exist.
Through these crossing experiments, we demonstrate that P. drummondii has
a sporophytic SI system, suggesting that an independent evolution of SI
occurred in the lineage containing Phlox. We map this novel S-locus and
find that the genomic region containing the S-locus is associated with
intraspecific variation in SI in one of the three mapping populations.
Although further work is necessary to clarify the conditions under which
quantitative variation in SI represents a transitional pathway to complete
SC, our study reveals the underlying genetic architecture upon which
selection could act to drive this frequent and evolutionarily significant
transition.