Discussion
Research on the degree of local adaptation in plant communities is
urgently needed to inform ecosystem restoration efforts (Bischoff et al.
2006, Vander Mijnsbrugge et al. 2010, Bischoff et al. 2010, Breed et al.
2018). Here, we devised a common garden experiment using both
cleistogamous and chasmogamous seeds of D. californica and
expected to see a local advantage for seeds of both types. However, we
did not find any evidence for local seeds outperforming seeds sourced
from other populations (nonlocal seeds) at either of our common garden
sites. These results align with the findings of Hereford (2010) who, in
a review of reciprocal transplant experiments, found that mating system
does not generally influence local adaptation. Instead, we found that
seeds of both types sourced from the north of our HD common garden
performed significantly better than seeds sourced both locally and from
more southern locations.
An absence of local adaptation could stem from intermediate levels of
either inbreeding or gene flow, or a lack of strong divergent selective
pressure on either of our common garden populations (Lenormand 2002,
Hereford 2010). Another possibility for why we may not have seen local
adaptation could be because our study looked exclusively at germination.
Adaptation patterns may come from the accumulation of small fitness
advantages over a plant’s life history, which are not always consistent
with those of the establishment stage (Rice & Knapp 2008, Jin et al.
2020).