Combining Historical Biogeography with Niche Modeling in the Caprifolium Clade of Lonicera (Caprifoliaceae, Dipsacales)

Abstract

The Lonicera clade Caprifolium contains approximately 25 species distributed around the Northern Hemisphere, including in the Mediterranean climates of California and Europe. We sequenced the second intron of LFY to help resolve relationships within the clade where the internal transcribed spacer and chloroplast markers had previously failed to do so. Divergence time estimation and biogeographic analyses over the posterior distribution of dated trees suggest that a widespread ancestor was distributed across the Northern Hemisphere some 7-17 million years ago. Asian species form a sister group to a clade in which the European species are sister to the North American species. We use climatic niche modeling and divergence time estimates to explore the evolution of climate variables in the group. Principal component analyses help to identify instances of convergence, especially between distantly related species in the Mediterranean basin and in the chaparral of California. We document several cases of significant divergence between sister species in eastern North America and western North America. Climatic models were projected from one continent into the others (e.g., North American species projected into Asia and Europe) to examine whether species living in these areas occupy similar climates. This study demonstrates the utility of combining niche modeling with historical biogeographic analyses and documents significant climatic niche evolution within a group of species distributed throughout the Northern Hemisphere. These results suggest a possible model for the origin of the Madrean-Tethyan disjunction pattern.