Diversification of Angraecum (Orchidaceae, Vandeae) in Madagascar: Revised Phylogeny Reveals Species Accumulation through Time Rather than Rapid Radiation

Abstract

Angraecum is the largest genus of subtribe Angraecinae (Orchidaceae) with about 221 species. Madagascar is the center of the diversity for the genus with ca. 142 species, of which 90% are endemic. The great morphological diversity associated with species diversification in the genus on the island of Madagascar offers valuable insights for macroevolutionary studies. Phylogenies of the Angraecinae have been published but a lack of taxon and character sampling and their limited taxonomic resolution limit their uses for macroevolutionary studies. We present a new phylogeny of Angraecum based on chloroplast sequence data (matk, rps16, trnL), nuclear ribosomal (ITS2) and 39 morphological characters from 194 Angraecinae species of which 69 were newly sampled. Using this phylogeny, we evaluated the monophyly of the sections of Angraecum as defined by Garay and investigated the patterns of species diversification within the genus. We used maximum parsimony and bayesian analyses to generate phylogenetic trees and dated divergence times of the phylogeny. We analyzed diversification patterns within Angraecinae and Angraecum with an emphasis on four floral characters (flower color, flower size, labellum position, spur length) using macroevolutionary models to evaluate which characters or character states are associated with speciation rates, and inferred ancestral states of these characters. The phylogenetic analysis showed the polyphyly of Angraecum sensu lato and of all Angraecum sections except sect. Hadrangis, and that morphology can be consistent with the phylogeny. It appeared that the characters (flower color, flower size, spur length) formerly used by many authors to delineate Angraecum groups were insufficient to do so. However, the newly described character, position of the labellum (uppermost and lowermost), was the main character delimiting clades within a monophyletic Angraecum sensu stricto. This character also appeared to be associated with speciation rates in Angraecum. The macroevolutionary model-based phylogeny failed to detect shifts in diversification that could be associated directly with morphological diversification. Diversification in Angraecum resulted from gradual species accumulation through time rather than from rapid radiation, a diversification pattern often encountered in tropical rain forests.

Afropectinariella (Vandeae, Orchidaceae), a new genus of the Angraecum alliance

“…In fact, African species of Angraecum belong to a group clearly distinct from that of members of the genus in Madagascar and the Indian Ocean islands ( Micheneau et al 2008 ). While investigating the diversification of the genus in Madagascar, Andriananjamanantsoa et al (2016) also confirmed the polyphyly of Angraecum s.l. and of all Angraecum sections with representatives in Madagascar, with the sole exception of section Hadrangis Schltr.…”

Evolution of crassulacean acid metabolism (CAM) as an escape from ecological niche conservatism in MalagasyBulbophyllum(Orchidaceae)

“…However, we found no strong (unambiguous) evidence for such a potential link between inferred historical changes in CO 2 (or temperature) and diversification across the full tree, and not at all for subclade C (Table S5). However, the crown age of this subclade and its corresponding shifts towards CAM and into the Eastern Lowlands (c. 7.36 Ma) remarkably coincide with the strengthening of the Indian Summer monsoon (c. 7 Ma; Gupta et al, 2015), resulting in increased moisture levels throughout eastern Madagascar and, possibly, the establishment of the Northwest 'Sambirano' (Yoder & Nowak, 2006;Buerki et al, 2013;Andriananjamanantsoa et al, 2016). In addition, these changes in monsoon climate could have created environmental instability across the comparatively older sub-humid and humid forest biomes of the Central Highlands and Eastern Coast of Madagascar, respectively (Cornet, 1974;Buerki et al, 2013).…”

Phylogenetic climatic niche conservatism and evolution of climatic suitability in Neotropical Angraecinae (Vandeae, Orchidaceae) and their closest African relatives

“…32.48 Mya, min. 22.2 Mya) we used published divergence times ( Givnish et al, 2015 ; Andriananjamanantsoa et al, 2016 ).…”