Nuclear phylogeography of the temperate tree species Chiranthodendron pentadactylon (Malvaceae): Quaternary relicts in Mesoamerican cloud forests

Background The Mexican hand tree or Canac (Chiranthodendron pentadactylon)
is a temperate tree species of cloud and pine-oak forests of southern
Mexico and Guatemala. The characteristic hand-shaped flower is used in
folk medicine and has constituted the iconic symbol of the Sociedad
Botánica de México since 1940. Here, the evolutionary history was
estimated through phylogeographic analyses of nuclear DNA sequences
obtained through restriction site associated DNA sequencing and ecological
niche modeling. Total genomic DNA was extracted from leaf samples obtained
from a representative number (5 to 10 per sampling site) of individuals
distributed along the species geographic range. In Mexico, population is
comprised by spatially isolated individuals which may follow the trends of
cloud forest fragmentation. Whether in Guatemala, Chiranthodendron may
constitute a canopy dominant species near the Acatenango volcano. The
distributional range encompasses geographic provinces separated by the
Isthmus of Tehuantepec. The objectives of the study were to: Estimate the
genetic structure to define whether the observed range disjunction exerted
by the Isthmus of Tehuantepec translates into separate populations. To
relate population divergence timing and demographic trends to historical
climate change, and to test hypotheses related to Pleistocene refugia.
Results Patterns of genetic diversity indicated high levels of genetic
differentiation between populations separated by the Isthmus. The western
and eastern population diverged approximately 0.873 MYA. Demographic
analyses supported a simultaneous split from an ancestral population and
rapid expansion from a small stock approximately 0.2 MYA corresponding to
a glacial period. The populations have remained stable since the LIG (130
KYA). SDM predicted a decrease in potential distribution in the LIG and an
increase during LGM (22 KYA), Mid-Holocene (6 KYA) and present times.
Conclusions Divergence estimations support the hypothesis that populations
represent Quaternary relict elements of a species with broader and
northernmost distribution. Pleistocene climatic shifts exerted major
influence on the distribution of populations allowing dispersion during
episodes of suitable climatic conditions and structuring during the first
interglacial with a time period length of 100 KYR and the vicariant
influence of the Isthmus. Limited demographic expansion and population
connectivity during the LGM supports the moist forest hypothesis model.