Abstract
Long-distance dispersal seems to be the main biogeographic event responsible for intriguing distribution patterns in plant groups in which sister taxa are separated by thousands of kilometers of distance across oceans and continents. The biotic and abiotic mechanisms behind such dispersal events are poorly understood and many attempts have been made to explain how plants can manage to disperse and survive these long journeys. The biogeographic history of Boraginaceae, a subcosmopolitan plant family with many disjunct clades, is here addressed and analyzed in the context of the different dispersal modes exhibited by the species. The lack of a clear pattern between the main dispersal events in Boraginaceae and the phylogenetic distribution of the dispersal modes indicates that no single dispersal mechanism can be associated with the events of dispersal in the family. Moreover, adaptations to different dispersal agents and unassisted dispersal modes in some clades might have promoted the diversification of Boraginaceae in various habitats across several continents. Our study reveals that long-distance dispersal is a very complex process that needs to be analyzed in the context of climatic and environmental changes and the response of plants and their dispersal vectors to these variable conditions.
Highlights
Disjunctive distribution patterns in many angiosperms are the result of rare long-distance dispersal (LDD) events that have taken place many times during evolution (e.g., Renner et al, 2000; Christenhusz and Chase, 2013; Chacón and Renner, 2014; Berger et al, 2016)
The age of the most recent common ancestor (MRCA) of Boraginales was dated to the Cenomanian stage in the Upper Cretaceous, ca. 96.2 million years ago (Ma; 95% high posterior density interval (HPD) = 85.0–107.4 Ma), which is congruent with the age reported in Luebert et al (2017) as for the crown node of Boraginales (i.e., 91.1 Ma, 95% HPD = 81.8–100 Ma)
The split between Wellstediaceae and Boraginaceae occurred in the Upper Cretaceous, ca. 79 Ma (95% HPD = 68.4–89.2 Ma) and the diversification Boraginaceae began during the Palaeocene, ca. 62.6 Ma (95% HPD = 54.6– 71.7 Ma)
Summary
Disjunctive distribution patterns in many angiosperms are the result of rare long-distance dispersal (LDD) events that have taken place many times during evolution (e.g., Renner et al, 2000; Christenhusz and Chase, 2013; Chacón and Renner, 2014; Berger et al, 2016). The unpredictability and complexity of such events, which imply the efficient dispersal of diaspores (seeds, fruits, plant parts) by means of biotic or abiotic vectors, and successful establishment and survival, depending on a range of factors, makes them very difficult to test (Nathan, 2006; Gillespie et al, 2012). In spite of this difficulty, LDD has become the most plausible explanation to many disjunctive plant distributions, especially for clades that have diversified after the Cretaceous continental break-up (de Queiroz, 2005; McGlone, 2005; Sanmartín et al, 2007). This kind of relationship has been shown before (e.g., Edwards and Westoby, 1996) it is still not well understood if the dispersal modes in angiosperms could be related to the incidence of long-distance dispersal or to the biogeographic patterns of a given clade
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