Niche conservatism in the Mesoamerican seasonal tropical dry forest orchid Barkeria (Orchidaceae)

Abstract

The aim of this paper is to investigate if speciation in allopatric species in Barkeria occurred in a scenario of ecological niche conservatism. Barkeria is a Mesoamerican orchid genus with fifteen species found in scattered forests in the Pacific mountains of Mesoamerica. Most species grow in seasonal tropical dry forests and a few also occupy oak, pine and pine-oak forests. Phylogenetic, molecular dating, ecological niche modeling and niche conservatism analyses were performed to determine phylogenetic relationships among species and to test for patterns between species relatedness and ecological niche traits. Bayesian phylogenetic analyses were conducted with nuclear and plastid DNA markers. Ecological niche modeling was run in MaxEnt. Evolutionary models of niche and climatic distances were estimated to determine if the niches in the Barkeria tree were conserved and if speciation in pairs of allopatric sister species retrieved in the phylogeny was influenced by climate. Barkeria is a young genus that has colonized the Pacific dry forest since the middle Pliocene to the Pleistocene. The fit of the phylogenetic Barkeria tree to a stasis model of evolution as well as the lack of phylogenetic signal under a Brownian motion model suggest strong niche conservatism of its species. However, factors other than climate influenced speciation in the allopatric sister species. The patchy distribution and differences in the vegetation of tropical dry forests of Mesoamerica as well as geographical barriers may have influenced speciation in Barkeria.