Did the Sunda-Sahul Biotic Exchange result in plant diversification? A case study of switching disperser communities and fruit traits in Aglaia (Meliaceae)

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The Sunda continental shelf (including Peninsular Malaysia, Brunei and parts of Indonesia) and Sahul continental shelf (including Australia and New Guinea) collided for the first time 25 Mya. This collision for the first time facilitated the exchange of biotas that had evolved in isolation on each shelf. This “Sunda-Sahul Biotic Exchange” had a significant effect on the biodiversity of the region, but a key question remaining is whether the exchange drove the diversification of biota. Lineages that jumped continental shelves were exposed to novel selection pressures, and we hypothesise that this led to the divergence of traits. To test this hypothesis, we are seeking funding to conduct a case study on the effect of the Sunda-Sahul Biotic Exchange on fruit traits in Aglaia (Meliaceae). Aglaia is a genus of c. 127 tropical tree species distributed across the Sunda and Sahul shelves, with remarkable diversity in fruits. Species have been reported to be dispersed either by primates, flying birds, or the flightless cassowary. Given the stark differences in disperser communities across the islands of the Sunda and Sahul shelves – and particularly the absence of primates on Sahul – we aim to test whether the different disperser communities drove the diversity of fruit traits in Aglaia as it migrated across the Sunda and Sahul shelves. To do this, we intend to achieve three main objectives over three years. Firstly, we will generate a robust, species-complete phylogeny of Aglaia and related genera using next-generation sequencing of targeted loci using a custom bait-kit. Secondly, we will conduct an in-depth characterisation of Aglaia fruits through developmental, anatomical and chemical analyses conducted on herbarium and field-collected specimens. Fruit trait evolution in Aglaia will then be reconstructed in a phylogenetic framework. Thirdly, we will implement cutting-edge analyses to test whether switches in fruit morphology were driven by differences in disperser communities. This will be done initially by reconstructing the biogeographic history of Aglaia and using phylogenetic comparative models to test whether biogeographic jumps are correlated with fruit trait switches. Subsequent to this, we will build a spatially explicit mechanistic model in the new eco-evolutionary simulation engine gen3sis, to explicitly test whether the differences in disperser communities in new biogeographic areas are causing fruit trait diversification, and exclude the possibility that it is due to other abiotic factors such as climate, or neutral processes such as genetic drift. Ultimately, this project will give new insight into the Sunda-Sahul Biotic Exchange and other similar biotic exchange events worldwide, and shed light on the processes leading to the evolution of diversity in a megadiverse hotspot.