Historical biogeography of 'Breynia' (Phyllanthaceae): what caused speciation?

Abstract

Aim. The dated phylogeny of 'Breynia' (including 'Sauropus') was used to analyse historical biogeographical patterns and to compare the speciation events with tectonic occurrences and biotic and abiotic aspects. Location. Southeast Asia, Malesia and Australia. Methods. Existing molecular markers ('trnS-trnG, accD-psaI', 'PHYC' and ITS)were used in BEAST to make a Bayesian age estimate with an exponential relaxed molecular clock. The resulting cladograms and maximum clade credibility (MCC) tree were used as input in statistical dispersal-vicariance analysis(S-DIVA option in the RASP package). Results. 'Breynia' originated 25-20 Ma in Thailand (western part of northern to southern Thailand) up to peninsular Malaysia. Dispersal occurred in various directions (India+Sri Lanka, China+Indochina, Malesia+Australia) establishing widespread species. Most species evolved locally in the area of origin and a relatively high number of species form limestone endemics. Main conclusions. There is little correlation between tectonic movements and dispersal patterns in 'Breynia'. Only the dispersal over Wallace's Line occurred when stepping stones were in place. Speciation, especially in the area of origin seems to be linked to soil (limestone endemics) and pollination, as indicated by the presence of deviating inflorescences in B. subgen. 'Sauropus' (no pollinators are known yet) and the obligate moth pollination in B. sect. 'Breynia'. Moreover, B. sect. 'Breynia' and three widespread species of B. subgen. Sauropushave (more) fleshy fruits and all these taxa generally have wide distributions, probably because of bird dispersal.