Conservation genomics of Wyethia reticulata (Asteraceae)

Wyethia reticulata is a rare perennial herb found only on gabbro-derived
soils of the Pine Hill formation in the Sierra Nevada foothills of El
Dorado County, California. Wyethia reticulata is capable of both
vegetative (clonal) and sexual reproduction, although the former is
thought to be more common than the latter, with sexual reproduction tied
to fire. The potential dominance of vegetative reproduction has
conservation implications for W. reticulata, as populations could appear
healthy in terms of stand density, while losing genetic diversity due to a
lack of sexual recruitment. Past genetic assessments of W. reticulata
relied on low-resolution markers from a small number of populations and
did not directly address conservation issues. Here, double-digest random
amplified DNA sequencing was used to develop a high-resolution genomic
dataset for a sample of 168 W. reticulata samples from seven locations
that represent every known population center of the species. The data was
used to 1) calculate the frequency of asexual reproduction, 2) determine
which populations contain unique genetic variation, and 3) test whether
there are any ecological correlates of genetic patterns. In contrast to
past genetic research, the results presented here indicate that clonality
is not common; less than 2% of plants were identified as being derived
from asexual reproduction. Nevertheless, some locations seem to be more
affected by asexuality than others; the index of association varied from
4.4 to 19.4 (average = 10.9). Genetic differentiation among locations was
low (Fst 0.03-0.04). However, clustering identified three distinct
population segments that were not previously recognized. Elevation was the
only environmental variable significantly associated with genetic
differentiation. Based on these results, it is recommended that
conservation effort be focused on genetically isolated population
segments.