Abstract
AimThe aim of this study was to resolve the phylogenetic placement of island taxa, reconstruct ancestral origins and resolve competing hypotheses of dispersal patterns and biogeographical histories for oceanic island endemic taxa within subgenus Plantago (Plantaginaceae).LocationJuan Fernández Islands, the Auckland Islands, Lord Howe Island, New Amsterdam Island, New Zealand, Tasmania, Falkland Islands, Rapa Iti and the Hawaiian Islands.TaxonIsland endemics within Plantago (Plantaginaceae), a globally distributed taxonomic group comprising approximately 250 species.MethodsWe use Bayesian phylogenetic and divergence time analyses and historical biogeographical analysis of molecular sequence data to infer the ancestral origins of the oceanic island species in Plantago.ResultsTaxa within subgenus Plantago form clades based on geographic proximities and challenge previous phylogenetic relationships and classification based on morphology. We infer that biogeographic histories of oceanic island taxa from multiple islands were shaped by dispersal at different scales and possibly by different types of birds. The highly remote Hawaiian Islands and Rapa Iti were colonized from North American taxa in a pattern corresponding to known migration routes of large marine birds, rather than from New Zealand as previously hypothesized. The island endemics of Juan Fernández, the Falkland Islands, Lord Howe, Auckland Islands and New Zealand are found to have sources in the nearest continental areas. The analyses confirm recent speciation within subgenus Plantago – which is particularly heightened in island lineages in Hawaii and Rapa Iti – but show slightly older divergence times than previous molecular dating studies.Main conclusionsUsing molecular data to infer ancestral ranges for plants with uncertain taxonomic relationships can greatly improve our understanding of biogeographical histories and help elucidate origins, dispersal modes and routes in widespread lineages with complex distribution patterns such as Plantago. We improve understanding of important floristic exchange areas between continents and islands as a result of long‐distance dispersal. We infer that a combination of both stepping stone dispersal and extreme long‐distance dispersal can shape insular floras, and that multiple floristic areas can be the sources of closely related island taxa. However, despite the successful dispersal of Plantago, radiation in island archipelagos is generally limited suggesting specific traits may limit diversification.
Highlights
For over a century, evolutionary biologists have investigated island taxa regarding their ancestral origins and evolutionary histories
Only 19 of the 45 island endemics in subgenus Plantago were available for previous phylogenetic analyses covering seven islands or island systems with known Plantago species
The ancestral ranges reconstructed at the more recent nodes are more straightforward and the analysis shows that the island endemics from Rapa Iti and the Hawaiian Islands have their most likely ancestral origins in North America, P. taquetii from Jeju is inferred to have origins in Asia
Summary
Evolutionary biologists have investigated island taxa regarding their ancestral origins and evolutionary histories. The remoteness of the oceanic islands, the extreme distance between the nearest landmasses as well as uncertainty in the taxonomic relationships have resulted in numerous and often competing hypotheses as to the biogeographical histories of the island taxa in Plantago (Dunbar‐Co et al, 2008; Hoggard et al, 2003; Meudt, 2012; Rahn, 1996; Rønsted et al, 2002; Tay et al, 2010a, 2010b). Only 19 of the 45 island endemics in subgenus Plantago were available for previous phylogenetic analyses covering seven islands or island systems with known Plantago species (most of these were restricted to Australasia [Meudt, 2012; Tay et al, 2010a], see Appendix I, Supporting Information) This severely limits the testing of biogeographic histories for island taxa in the globally distributed genus Plantago. | 709 responsible for the distribution of the taxa in a genus that is likely to be dispersed by birds across extreme long distances
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