Dispersal patterns in space and time: a case study of Apiaceae subfamily Apioideae

Aim: To analyse spatial and temporal patterns of dispersal events in the euapioids (Apiaceae subfamily Apioideae). Location: Worldwide, with an emphasis on the Northern Hemisphere. Methods: A phylogeny of euapioids was inferred from 1194 nuclear ribosomal DNA internal transcribed spacer (nrDNA ITS) sequences using Bayesian methods. The reconstruction of ancestral areas was performed simultaneously with phylogenetic inference using a Markov discrete phylogeographical model with Bayesian stochastic search variable selection (BSSVS). Routes with significant non-zero migration rates were identified using Bayes factors. For each significant track and each tree, the distribution of dispersals in time was scored and the asymmetry of dispersals was evaluated. Results: The root of the euapioid umbellifers was reconstructed at c. 44.51 Ma (95% highest posterior density interval: 39.11—51.55 Ma). The Eastern Asiatic Region was reconstructed as the most probable ancestral area for the root of the tree. Seventeen migration routes have significant non-zero migration rates. Five of these tracks represent long-distance transoceanic routes: (1) western Eurasia—North America, (2) Eastern Asiatic Region—North America, (3) Australia—Neotropical Kingdom, (4) Australia—Neantarctic, and (5) Neotropical Kingdom—sub-Saharan Africa. Most dispersal events occurred among the areas that comprise the major diversification centres of apioid umbellifers: western Eurasia and the Mediterranean, Irano-Turanian and Eastern Asiatic regions. The floristic exchange among these regions was more or less symmetrical in all directions and continuous in time. The exchange between North America and the Eastern Asiatic Region was asymmetrical; the asymmetry of dispersals between western Eurasia and North America was less pronounced and not statistically significant. Floristic exchange was significantly asymmetrical for the Nearctic—Neotropical Kingdom, Nearctic—Neantarctic, western Eurasia—sub-Saharan Africa, and western Eurasia—Siberia migration tracks. Main conclusions: The observed dispersal pattern — intense and symmetrical within the same climatic zone versus scarce and often unidirectional between climatic zones or along long-distance transoceanic tracks — suggests that both the availability of suitable habitats and geographical barriers have played crucial roles in determining the present distribution of euapioid umbellifers.