Geographic Range Dynamics Drove Ancient Hybridization in a Lineage of Angiosperms

Elucidating the dynamic distribution of organismal lineages has been central to biology since the nineteenth century, yet the difficulty of combining biogeographic methods with shifts in habitat suitability remains a limitation. This integration, however, is critical to understanding geographic distributions, present and past, as well as the time-extended trajectories of lineages. Here, we link previous advances in phyloclimatic modeling to develop a framework that overcomes existing methodological gaps by predicting potential ecological and geographic overlap directly from estimated ancestral trait distributions. We show the utility of this framework by focusing on a clade in the montane angiosperm genus Heuchera, which is noteworthy in that it experienced ancient introgression from circumboreally distributed species of Mitella, lineages now ~1,300 km disjunct. Using this system, we demonstrate an application of ancestral state reconstruction to assess geographic range dynamics in a lineage lacking a fossil record. We test hypotheses regarding inferred past geographic distributions and examine the potential for ancient geographic contact. Application of this multifaceted approach suggests potential past contact between species of Heuchera and Mitella in western North America during cooler periods of the Pleistocene. Integration of niche models and phylogenetic estimates suggests that climatic cooling may have promoted range contact and gene flow between currently highly disjunct species. Our approach has wide applicability for testing hypotheses concerning organismal co-occurrences in deep time.