Patterns in the genetic structure of 49 lowland rain forest tree species co-distributed on opposite sides of the Northern Andes

The Andes are a major dispersal barrier for lowland rain forest plants and
animals, yet hundreds of lowland tree species are distributed on both
sides of the Northern Andes, raising questions about how the Andes
influenced their biogeographic histories and population genetic structure.
To explore these questions, we generated standardized datasets of
thousands of SNPs from paired populations of 49 tree species
co-distributed in rain forest tree communities located in Panama and
Amazonian Ecuador and calculated genetic diversity (π) and absolute
genetic divergence (dXY) within and between populations, respectively. We
predicted (1) higher genetic diversity in the ancestral source region
(east or west of the Andes) for each taxon, and (2) correlation of genetic
statistics with species attributes, including elevational range and
life-history strategy. We found that genetic diversity was higher in
putative ancestral source regions, possibly reflecting founder events
during colonization. We found little support for a relationship between
genetic divergence and species attributes except that species with higher
elevational range limits exhibited higher dXY, implying older divergence
times. One possible explanation for this pattern is that dispersal through
mountain passes declined in importance relative to dispersal via
alternative lowland routes as the Andes experienced uplift. We found no
difference in mean genetic diversity between populations in Central
America and the Amazon. Overall, our results suggest that dispersal across
the Andes has left enduring signatures in the genetic structure of
widespread rain forest trees. We outline additional hypotheses to be
tested with species-specific case studies.