The diversification of Pterocarpus (Leguminosae: Papilionoideae) was influenced by biome-switching and infrequent long-distance dispersal

Abstract

Aim: Phenotypes which evolved for dispersal over ecological timescales may lead to significant macroevolutionary consequences, such as infrequent long-distance dispersal and diversification in novel environments. We aimed to reconstruct the phylogenetic history of Pterocarpus (Leguminosae/ Fabaceae) to assess whether seed dispersal phenotypes help to explain the current biogeographical patterns of this group. Location: Pantropical. Taxon: The Pterocarpus clade, particularly Pterocarpus (Leguminosae/Fabaceae). Methods: We sequenced ~300 nuclear loci captured using Angiosperms-353, a genomic 'bait set' for flowering plants, from which we generated a time-calibrated phylogenomic tree. To corroborate this, we also generated a time-calibrated phylogenetic tree from data-mined Sanger-sequencing data. We then collated distribution data and fruit dispersal morphology traits to compare trait-dependent and trait-independent biogeographical models, allowing us to assess whether dispersal traits influenced the spatio-temporal evolution of Pterocarpus. Finally, using the results of these model tests, we estimated the ancestral ranges and biomes of Pterocarpus species to better understand their biogeographical history. Results: We recovered well-supported phylogenetic relationships within Pterocarpus, within which there were two subclades - one Neotropical and the other Palaeotropical. Our divergence date estimates suggested that Pterocarpus largely diversified from around 12 Ma, during the Miocene. Trait-dependent biogeographical models were rejected for both range and biome evolution within Pterocarpus, but models parameterising dispersal were supported. Pterocarpus largely diversified in the Neotropics, followed by dispersal and diversification into Africa and Asia, with later dispersal into Australasia/Oceania. The neotropical subclade of Pterocarpus underwent multiple biome switches between moist forest and dry forest, while in palaeotropical Pterocarpus we reconstructed multiple switches between moist forest and grassland. Main conclusions: Overall, our analyses suggest that Pterocarpus underwent infrequent cross-continental dispersal and adaptation to novel biomes. While this was minimally impacted by fruit dispersal syndromes, shifts between moist and arid environments precipitated by long-distance dispersal and environmental change have played an important role in diversification within Pterocarpus since the Miocene.