Abstract
BackgroundMadagascar’s rain forests are characterized by extreme and uneven patterns of species richness and endemicity, the biogeographic and evolutionary origins of which are poorly understood.MethodsHere we use a time-calibrated phylogeny of a dominant group of trees in Madagascar’s eastern rain forests, Canarium, and related Burseraceae (Canarieae), to test biogeographic hypotheses regarding the origin and radiation of the flora of this unique biome.ResultsOur findings strongly support the monophyly of Malagasy Canarium, suggesting that this clade represents a previously undocumented in situ radiation. Contrary to expectations of dispersal from Africa during the Oligocene, concurrent with the formation of Madagascar’s rain forest biome, our analyses support a late Miocene origin for Malagasy Canarium, probably by long distance dispersal from Southeast Asia.DiscussionOur study illustrates the importance of considering long distance dispersal as a viable explanation for clades with pantropical distributions diversifying subsequent to the Oligocene, and it highlights the formation of the Indo-Australian Archipelago and associated fast-moving equatorial surface currents, suggesting an under-appreciated evolutionary link among tropical centers of endemism.ConclusionsWe postulate that the relatively recent establishment and radiation of Canarium in Madagascar may have been facilitated by the highly stochastic climates associated with these forest ecosystems.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0483-1) contains supplementary material, which is available to authorized users.
Highlights
Madagascar’s rain forests are characterized by extreme and uneven patterns of species richness and endemicity, the biogeographic and evolutionary origins of which are poorly understood
Using our dated phylogenetic tree as a foundation for biogeographic analyses, we argue that Canarium arrived in Madagascar through geologically recent long distance dispersal from Southeast Asia, coincident with the formation of the Indo-Australian Archipelago (IAA)
Given the similarity between the analyses, we focused our discussion on fossil-tip calibrations, as they accommodated the phylogenetic uncertainty surrounding the placement of the Canarium fossil within a non-monophyletic group by allowing it to vary in position along the stem leading to the crown of the wet forest Canarieae
Summary
Madagascar’s rain forests are characterized by extreme and uneven patterns of species richness and endemicity, the biogeographic and evolutionary origins of which are poorly understood. During the early development of Madagascar’s rain forests in the Oligocene, predominant marine currents were eastward, favoring colonization from Africa [7]. Movement by ocean current from Southeast Asia in particular probably became intermittently feasible from the Oligocene (34–23 Ma) [3, 7, 10, 11]. This was due to tectonic shifts in the positions of Indian and Southeast Asian landmasses, and gradual westward reconfiguration of the predominant current [10, 11]. By the early Miocene this reconfiguration was complete, and marine dispersal from Africa to Madagascar would be far less likely [7]
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