Genetic structure and diversity of the declining orchid Gymnadenia conopsea in Scandinavia: Implications for conservation and management

Understanding how historical versus contemporary processes shape
population genetic structure and diversity is important to design
effective management actions for threatened species. We genotyped 1,834
SNPs in 1,120 individuals in 110 Scandinavian populations of the declining
orchid Gymnadenia conopsea, in three different habitat types, to examine
if genetic structure was related to wind speed, terrain ruggedness, forest
cover, and seasonality at the landscape scale, and if genetic diversity
increases with census population size, and is higher in core habitats (fen
and meadow) than in marginal, coastal habitats. We identified three
genetic clusters and pronounced isolation by distance, consistent with two
independent colonization routes after last glacial maximum, followed by
admixture. Effective population size was highest in the admixed cluster.
Estimates of effective migration indicated reduced gene flow along the
Atlantic coast, between coastal and inland populations, and among southern
meadow populations. High landscape resistance to gene flow was associated
with complex topography and pronounced seasonality. Genetic diversity
increased with population size, but did not vary among habitat types.
Genetic diversity peaked in core habitats, i.e., southern meadows and
inland fens along the Scandes mountains. Lowest genetic diversity was
found on the Atlantic coast and in a few scattered populations. Current
genetic structure suggests a strong legacy of historical events, and the
high genetic diversity documented in the main Scandinavian range indicates
that current viability and future adaptation potential is high. To
maintain genetic diversity and connectivity between genetic groups, it is
particularly important to preserve southern meadow populations, which
currently are in strong decline. Generally, results illustrate how a
declining species can help us understand the impact of historical and
current processes, how landscape genetic data can inform proactive
conservation, and how a slow genetic response to fragmentation can allow
time to maintain genetic diversity through habitat restoration and
management.