In-situ diversification and regional attributes shape asymmetric diversity of Miliusa (Annonaceae) in tropical Asia.

Abstract

AimWe examine biogeography and speciation patterns in Miliusa Lesch. ex A. DC. ([~]65 species) distributed in tropical Asia to understand the uneven distribution of its extant diversity. LocationTropical Asia TaxonMiliusa (Annonaceae) MethodsPhylogenetic reconstruction was performed using six plastid markers across 52 species using both ML and BI approaches. Divergence times were estimated using two fossil calibrations and an optimised relaxed clock, and ancestral areas were inferred with BioGeoBEARS. Speciation rates were examined using ClaDS and the DR statistic, and community structure was assessed using phylogenetic diversity metrics. ResultsMiliusa likely originated in the mid-Miocene, with Indo-Burma and peninsular India (PI) as its ancestral range. Its extant diversity is primarily attributed to in-situ speciation, with dispersal or vicariance playing limited but important roles in PI, and Wallacea and Sahul. Lineages in Indo-Burma began accumulating in the mid-Miocene, preceding those in PI ([~]10 Myr) and Wallacea and Sahul ([~]5 Myr). PI showed signs of lineage saturation and had lower speciation rates compared to Wallacea and Sahul and Indo-Burma, both of which had similar rates. All regions exhibited phylogenetic clustering, but Indo-Burma and PI differed in their sensitivity to phylogenetic depths. Main conclusionsThe uneven diversity of Miliusa is shaped by time for speciation, age, and dispersal, although their relative influence varies across regions. In Indo-Burma, long-term geo-climatic stability and greater niche availability likely facilitated the persistence of lineages, rapid speciation, and dispersal, making it an evolutionary hotspot for Miliusa. In contrast, PI exhibited lower richness and speciation rates despite being old, likely due to the contraction of wet habitats in the Miocene that limited available niches for speciation. Lineages in Wallacea and Sahul show typical island-like radiations, with speciation rates comparable to the larger and more geo-climatically stable Indo-Burma, despite their more recent origin. Overall, our results highlight the role of Miocene-driven climatic vicariance and Pliocene-Pleistocene climatic fluctuations in shaping the diversification dynamics and regional diversity patterns across tropical Asia.