Data from: Halfway encounters: meeting points of colonization routes among the southern beeches Nothofagus pumilio and N. antarctica

The Patagonian region is characterized by a complex biogeographic history,
with evidence of deep phylogeographic breaks shared among species. Of
particular interest to conservation is the nature of colonization and
settlement patterns after the last glacial period, including the detection
of secondary contact between different lineages and/or hybridization among
related species around phylogeographic breaks. Here we studied population
demography and past hybridization of two widespread tree species endemic
to South America, Nothofagus pumilio and N. antarctica. Using 8 nuclear
microsatellites we genotyped 41 populations of both species. Genetic
variation and structure across the geographic region were evaluated within
and among species and the past demographic history of hybridization
between the two species was inferred using Approximate Bayesian
Computation (ABC). Northern and southern lineages were identified in each
species, and Bayesian clustering revealed their convergence at mid
latitudes (42°S). Spatial genetic structure (SGS) also indicated the
existence of a genetic discontinuity at these latitudes, which is in
agreement with previous data from maternal DNA markers. Several
populations around 42–44°S presented high levels of genetic diversity with
a decrease toward southern populations. Even though the species are
clearly differentiated (G’ST = 0.335), admixed gene pools were observed in
both species. Two independent runs of ABC suggested that inter species
admixture-like patterns occurred within the timescale of the Last Glacial
Maximum (around 20,000 BP). We also provide evidences of recent and
bi-directional hybridization/introgression between the two Nothofagus
species and describe features of the populationś demography in the past.
The settlement of a secondary contact zone in Nothofagus species around
42–44°S coincides with the phylogeographic breaks and hotspots of genetic
diversity found in other plant and animal species in Patagonia,
highlighting its importance as reservoir of diversity. The
characterization of the population history of native species can
contribute substantially to long-term conservation and management
policies.