Allopatric speciation is more prevalent than parapatric ecological divergence in tropical montane systems (Asteraceae: Piofontia)

Abstract

ABSTRACTElucidating how species accumulate in diversity hotspots is an ongoing debate in evolutionary biology. The páramo, in the Northern Andes, has remarkable high indices of plant diversity, endemicity, and diversification rates. A hypothesis for explaining such indices is that allopatric speciation is high in the páramo given its island-like distribution; an alternative hypothesis is that the altitudinal gradients of the Andean topography provides a variety of niches that drive vertical parapatric ecological speciation. A formal test for evaluating the relative roles of allopatric speciation and parapatric ecological divergence has not been carried out. The main aim of our study is to test which kind of speciation is more common in the páramo. We developed a framework incorporating phylogenetics, species’ distributions, and a morpho-ecological trait (leaf area) to compare sister species and infer whether allopatry or parapatric ecological divergence caused their speciation. We applied our framework to the species-rich genus Piofontia (63 spp.) and found that the majority of speciation events in Piofontia, (80%) have been driven by allopatric speciation events, while a smaller fraction (13%) are attributed to parapatric ecological divergence; one event produced inconclusive results (7%). We conclude that páramo autochthonous diversification is primarily driven by allopatric speciation.