Phylogeny and biogeography of the sandalwoods (Santalum, Santalaceae): repeated dispersals throughout the Pacific

Abstract

Results of the first genus-wide phylogenetic analysis for Santalum (Santalaceae), using a combination of 18S-26S nuclear ribosomal (ITS, ETS) and chloroplast (3' trnK intron) DNA sequences, provide new perspectives on relationships and biogeographic patterns among the widespread and economically important sandalwoods. Congruent trees based on maximum parsimony, maximum likelihood, and Bayesian methods support an origin of Santalum in Australia and at least five putatively bird-mediated, long-distance dispersal events out of Australia, with two colonizations of Melanesia, two of the Hawaiian Islands, and one of the Juan Fernandez Islands. The phylogenetic data also provide the best available evidence for plant dispersal out of the Hawaiian Islands to the Bonin Islands and eastern Polynesia. Inability to reject rate constancy of Santalum ITS evolution and use of fossil-based calibrations yielded estimates for timing of speciation and colonization events in the Pacific, with dates of 1.0-1.5 million yr ago (Ma) and 0.4-0.6 Ma for onset of diversification of the two Hawaiian lineages. The results indicate that the previously recognized sections Polynesica, Santalum, and Solenantha, the widespread Australian species S. lanceolatum, and the Hawaiian species S. freycinetianum are not monophyletic and need taxonomic revision, which is currently being pursued.

Are islands the end of the colonization road?

“…Longdistance mainland-to-island colonizations have been reported in plants (e.g. [47,48]) and we predict that further phylogeographic studies, involving far islands or archipelagos as well as continents, might shed light on the pattern and frequency of long-distance colonization in both directions.…”

New Caledonia: a very old Darwinian island?

“…The same applies for Placostylus land snails, the sister group of which involves both the recently emerged Lord Howe Island and New Zealand ( Trewick et al in press). The New Caledonian sandalwood, Santalum austrocaledonicum, also differentiated recently, in this case from Vanuatu species 1-1.5 Ma (Harbaugh & Baldwin 2007 (Barker et al 2007). The New Caledonian freshwater shrimp genus Paratya (Page et al 2005) and galaxiid fishes (Waters et al 2000), sisters respectively to an Australian and a New Zealand group, are dated as younger than 12 and 9 Ma, respectively.…”

New Guinea highland origin of a widespread arthropod supertramp

“…Similarly, drynaroid ferns possibly originated in southeast Asia and West Malesia, and then dispersed across Indonesia and the Philippines to New Guinea (Schneider et al 2008). Molecular phylogenetics of sandalwoods suggests an Australian origin followed by complex long-distance dispersal patterns throughout the Pacific as far west as Juan Fernandez (Harbaugh & Baldwin 2007).…”