Historical Biogeography and Temporal Diversification in Symphoricarpos (Caprifolieae, Caprifoliaceae, Dipsacales)

Abstract—

The major aim of this paper was to investigate temporal diversification within Symphoricarpos (Caprifoliaceae, Dipsacales). We used recently published molecular sequences, along with fossil data, to examine when Symphoricarpos may have arrived in the New World and if current distributional patterns can be explained by data based on biogeographic, climatological, and geological events. We simultaneously estimated the phylogeny and divergence times within Symphoricarpos and related Caprifolieae species using BEAST. Based on these phylogenetic and divergence time estimations we reconstructed ancestral areas using the dispersal-extinction-cladogenesis (DEC) method implemented in Lagrange. For Symphoricarpos, our phylogenetic results inferred using BEAST were in strong agreement with previous studies, with a well-supported clade containing the North American species that was sister to the lone Asian species. Our divergence time results suggest that the North American species originated in the late Oligocene to mid Miocene (12‐25 million years ago) and quickly diversified. The DEC area reconstructions suggest that after entering the North American continent from Asia, species of Symphoricarpos became widespread across the continent, followed by range restrictions to that of what we see today. Although several recent studies have argued for the idea of phylogenetic niche conservatism as a general explanation for characterizing broad biogeographic patterns, our data suggest significant niche evolution within the North American species of Symphoricarpos, especially in regard to taxa found in the southwestern parts of the USA and Mexico. These observed biome shifts from mesic forest habitats to a much drier habitat appear to have happened across a highly diverse landscape in which species of Symphoricarpos occur. These results, along with results from other plant taxa, support the hypothesis that a climate shift in western North America played a role in the assemblage of the current flora via migration, as well as in situ adaptation in combination with diversification.