Inbreeding depression in artificial selection lines of Ipomoea purpurea

Inbreeding depression is a central parameter underlying mating system
variation in nature and one that can be altered by environmental stress.
Although a variety of systems show that inbreeding depression tends to
increase under stressful conditions, we have very little understanding
across most organisms how the level of inbreeding depression may change as
a result of adaptation to stressors. In this work we examined the
potential that inbreeding depression varied among lineages of Ipomoea
purpurea artificially evolved to exhibit divergent levels of herbicide
resistance. We examined inbreeding depression in a variety of
fitness-related traits in both the growth chamber and in the field, paired
with an examination of gene expression changes. We found that, while
inbreeding depression was present across many of the traits, lineages
artificially selected for increased herbicide resistance often showed no
evidence of inbreeding depression in the presence of herbicide, and in
fact, showed evidence of outbreeding depression in some traits compared to
non-selected control lines and lineages selected for increased herbicide
susceptibility. Further, at the transcriptome level, the resistant
selection lines had differing patterns of gene expression according to
breeding type (inbred vs outcrossed) compared to the control and
susceptible selection lines. Our data together indicate that inbreeding
depression may be lessened in populations that are adapting to regimes of
strong selection.