Abstract
The high genetic diversity of rear-edge refugia has been predicted to
result from repeated retreats of species’ ranges to low latitudes during
glacial periods in the course of Quaternary climate change. However, a
few recent empirical studies of cold tolerant plants revealed an
opposite pattern. We investigate whether current populations of the
cold-adapted and range-restricted Bupleurum euphorbioides in the
Baekdudaegan, South Korea and North Korea, could be interglacial
refugia, and document how their rear-edge populations differ genetically
from those of typical temperate species. Phylogeographic analysis and
ecological niche modeling (ENM) were used. Genetic structure was
analyzed using microsatellite markers and chloroplast DNA sequences. The
congener B. longiradiatum was included as a typical temperate
plant species. Despite having almost identical life history traits,
these congeneric species exhibited contrasting patterns of genetic
diversity. ENM revealed a wide range expansion along the Korean
mountains to northern Far East Russia (Primorsky) during the Last
Glacial Maximum, but not during the last interglacial. Thus, we
hypothesize that B. euphorbioides retreated to refugia following
maximum range contraction during interglacial periods. Unlike
populations in the central region, the rear-edge populations were
genetically impoverished and uniform, both within populations and in
pooled regional populations. The rear-edge has endured at least one past
interglacial, contributing to the species’ genetic diversity. We believe
that such genetic variation in the cold-adapted B. euphorbioides
gives it the necessary adaptations that will enable it to survive an
upcoming favorable environment (the next glacial), unless there is
artificial environmental change.