Global biogeography and diversification of palms sheds light on the evolution of tropical lineages. I. Historical biogeography
Correspondence: William J. Baker, Royal Botanic Gardens, Kew, Richmond, Surrey, TW9 3AB, UK.
Palms (Arecaceae/Palmae) are a model group for evolutionary studies in the tropics. Family-wide data on taxonomy, phylogenetics and distribution are now available, but a general framework of palm evolution is still lacking. The overall aim of this study, published in two companion papers, is to seek evolutionary explanations for the geographical distribution of palm lineages and species diversity patterns at global and regional levels. In this first paper we undertake a detailed analysis of palm biogeography for all major lineages in a global context, comparing our results to the fossil record, molecular dating studies and previously established biogeographical hypotheses for the family.
A dated phylogeny of all palm genera and distributional data were used to infer ancestral areas. A global model of area evolution for tropical lineages was formulated and ancestral areas were reconstructed using a maximum likelihood approach under the dispersal–extinction–cladogenesis model.
The crown node divergence of palms and divergences of all five subfamilies occurred before the end of the Cretaceous within Laurasian regions. Early range expansions into South America took place in the stem lineages of subfamilies Arecoideae and Ceroxyloideae, and into Africa and South America in Cretaceous lineages within subfamily Calamoideae. The largest subfamily Arecoideae underwent its early diversification history in South America and has been an important source of lineages expanding into other regions, notably in the major Indo-Pacific tribe Areceae. In contrast, the history of subfamily Coryphoideae was primarily Laurasian, supporting earlier boreotropical hypotheses for the group. Dispersals across Wallace's Line are prevalent in major groups of Arecoideae, Calamoideae and Coryphoideae, both before and after the Miocene geological evolution of the Malesian Archipelago.
We present the first robust biogeographical hypothesis for the evolution of palms in space and time. Although palms show evidence of dispersal limitation, our findings highlight the role of long-distance dispersal events in the establishment of major biogeographical patterns of palm clades. This is consistent with the growing evidence for long-distance dispersal as a major mechanism underpinning the distribution of tropical lineages.