Abstract
Long-lived species of trees, especially conifers, often display weak patterns of reproductive isolation, but clear patterns of local adaptation and phenotypic divergence. Discovering the evolutionary history of these patterns is paramount to a generalized understanding of speciation for long-lived plants. We focus on two closely related yet phenotypically divergent pine species, Pinus pungens and P. rigida, that co-exist along high elevation ridgelines of the southern Appalachian Mountains. Based on genome-wide RADseq data, patterns of population structure for each species were uncorrelated to geography and the environment. Signals of admixture, however, were present range- wide. When combined with information from contemporary and historical species distribution models, these patterns are consistent with a complex evolutionary history of speciation. This was confirmed using inferences based on the multidimensional site- frequency spectrum, where demographic modeling inferred recurring gene flow since divergence (9.3 – 15.4 million years ago) and population size reductions that align in timing with the last interglacial period (∼120 – 140 thousand years ago). This suggests that phenotypic and genomic divergence, including the evolution of divergent phenological schedules leading to partial reproductive isolation, as previously documented for these two species, can happen rapidly, even between long-lived species of pines.
Competing Interest Statement
The authors have declared no competing interest.