Shift in ecological strategy helps marginal populations of shepherd's purse (Capsella bursa-pastoris) to overcome a high genetic load

The outcome of species range expansion depends on the
interplay of demographic, environmental and genetic factors.
Self-fertilizing species usually show a higher invasive ability than
outcrossers but selfing and bottlenecks during colonization also lead
to an increased genetic load. The relationship between genomic and
phenotypic characteristics of expanding populations has, hitherto,
rarely been tested experimentally. We analyzed how accessions of the
shepherd’s purse, C. bursa-pastoris, from the colonization front or
from the core of the natural range performed under increasing density
of competitors. First, accessions from the front showed a reduced
fitness than those from the core. Second, for all accessions,
competitor density impacted negatively both vegetative growth and
fruit production. However, despite their higher genetic load and lower
absolute performances, accessions from the front were less affected by
competition than accessions from the core. This seems to be due to
phenotypic trade-offs and a shift in phenology that allow accessions
from the front to avoid competition.