Niche evolution of the Neotropical tree genus Otoba in the context of global biogeography of the nutmeg family, Myristicaceae

Abstract

AimPlant distributions are influenced by species ability to colonize new areas via long-distance dispersal and propensity to adapt to new environments via niche evolution. We use Otoba (Myristicaceae), an ecologically dominant tree genus found in low-to-mid elevation wet forests, as a system to understand the relative importance of these processes within the Neotropics, a region characterized by high species richness and a diversity of biomes. LocationNeotropics and global TaxonOtoba and entire Myristicaceae MethodsWe resolve the first phylogeny of Otoba using targeted sequence capture phylogenomics. We pair this with the most densely sampled phylogeny of Myristicaceae to date, inferred using publicly available data. We then use phylogenetic comparative methods to infer biogeography and examine patterns of niche evolution. ResultsMyristicaceae has an Old World origin, with a single expansion event into the Americas. Divergence dates, fossil evidence, and a notable lack of long-distance dispersal are consistent with a Boreotropical origin of Neotropical Myristicaceae. Mirroring the rarity of dispersal at the family level, Otobas biogeography is marked by few biogeographic events: two expansions into Central America from a South American ancestor and a single dispersal event across the Andes. This limited movement contrasts with rapid climatic niche evolution, typically occurring across geographically proximate habitats. Main conclusionsContrasting with previous studies, long-distance dispersal does not need to be invoked to explain the pantropical distribution of Myristicaceae, nor the biogeography of Otoba. This likely results from the familys relatively large seeds that are dispersed by large-bodied vertebrates. Instead, rapid niche evolution in Otoba has facilitated its occurrence throughout mesic habitats of the northern Neotropics, including the Amazon rainforest and Andean montane forests. Otoba adds to a growing group of Neotropical plant clades in which climate adaptation following local migration is common, implying an important role of niche evolution in the assembly of the Neotropical flora. Significance statementSpecies distributions across the climatically and topographically heterogenous Neotropics are explained by a combination of local adaptation and dispersal. The relative importance of these mechanisms is clade dependent. We find that niche evolution in geographically proximal habitats is much more common than long-distance dispersal to preadapted regions in the tree genus Otoba, which includes both hyperdominant Amazonian species and narrow Andean endemics. The lack of long-distance dispersal is likely due to Otobas large seeds. Our results add to a growing body of literature demonstrating a key role of labile niche evolution across steep environmental gradients in Neotropical plant biogeography.