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A climate relict is of particular importance in evolutionary biology
because of its long-term survival in the face of climatic oscillations.
However, because their current distributions are usually restricted
and fragmented, many climatic relicts have extinction risks. Daphnimorpha
(Thymelaeaceae) is a Japanese endemic genus that comprises two species (D.
capitellata and D. kudoi) showing a disjunct distribution in the southern
part of Japan. These two species are endemic to a single mountain range.
In this study, we conducted population genetic analyses using genome-wide
single nucleotide polymorphism obtained from multiplexed inter-simple
sequence repeat genotyping by sequencing to reveal the
phylogeographic history and obtain conservation implications for the two
species. The results showed these two species may have been isolated since
the Tertiary period, indicating that they are climate relicts. In
addition, D. kudoi showed clear genetic differentiation between two
mountains (Mt. Nagata and Mt. Kuromi), with a decline in effective
population sizes during the last glacial period. In contrast, D.
capitellata showed no clear intraspecific genetic structure and its
effective population size was relatively stable. These differences could
be a result of differences in habitat preferences between the species. For
conservation, we should manage the two species based on the three
evolutionary significant units (ETUs; D. capitellata, D. kudoi population
on Mt. Nagata, and D. kudoi population on Mt. Kuromi). Considering the
limited gene flows among subpopulations and their small population sizes,
all ETUs require conservative attention to maintain or increase their
effective population sizes.
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