Drivers of speciation in large Myrtaceae genera (Eugenia, Syzygium)

Hyper-speciation events in large genera - using Eugenia and Syzygium as case studies

Eugenia fruits

Myrtaceae is an unusual angiosperm family in containing four genera comprising more than 500 species. Three of these, Eugenia, Syzygium, and Myrcia (c. 1000, 1050, and 770 species, respectively) are predominantly tropical rainforest trees, with the first two sharing much morphological similarity that has lead to their repeated synonymy. In each of these genera, rapid shifts in diversification rates have been demonstrated, likely due to i) evolution of key morphological or physiological innovations or ii) niche partitioning and founder effects in rapidly changing landscapes and climates. No hypotheses regarding specific factors driving divergence of large rainforest taxa have been rigorously tested however and there is little understanding of the extent to which these factors have shaped tropical rainforest biomes as we know them today.
Tropical rainforests account for between 3-6 % of earths dry surface and accommodate the majority of the world’s species. Preservation of these species from increasing pressure of human activities depends on our understanding of the species present in these biomes, how they evolved and their current and historical interactions. Eugenia and Myrcia are members of tribe Myrteae while Syzygium is in tribe Syzygieae; these two tribes form part of a (BKMMST) clade also containing tribes Backhousieae, Kanieae, Metrosidereae and Tristanieae.
This project seeks to infer common factors driving speciation in the large, rainforest genera Eugenia and Syzygium. A dated BKMMST phylogeny sampled to reflect species richness and geographical distribution is under analysis to detect rate shifts and to correlate these with biotic and abiotic factors. Biogeographical patterns explaining the current distribution of species within these genera are to be assessed in light of their evolutionary timescales, using dispersal-vicariance analysis and likelihood-based methods to determine if high speciation rate in these cases is indicative of the predominance of vicariance or dispersal in the assembly of species-rich continental biomes/groups.