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

View Article: PubMed Central - PubMed

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.

No MeSH data available.


Ancestral state reconstructions of floral characters in Angraecinae implemented in ‘diversitree’; colors represent character states of the labellum position (uppermost and lowermost) and pie charts represent the probability of ancestral states at nodes. C denotes taxa illustrated in the pictures to the right to represent the flower shape of each clade except for Jumellea which is represented by Jumellea comorensis (not sampled in the phylogeny). Photo: Andriananjamanantsoa.
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pone.0163194.g005: Ancestral state reconstructions of floral characters in Angraecinae implemented in ‘diversitree’; colors represent character states of the labellum position (uppermost and lowermost) and pie charts represent the probability of ancestral states at nodes. C denotes taxa illustrated in the pictures to the right to represent the flower shape of each clade except for Jumellea which is represented by Jumellea comorensis (not sampled in the phylogeny). Photo: Andriananjamanantsoa.

Mentions: Our results showed that a labellum in the lower position is plesiomorphic in Angraecinae, while an upper labellum is apomorphic and evolved at least five times independently (Fig 5). White flowers appear to be symplesiomorphic in Angraecinae, while green flowers are apomorphic and evolved independently several times in Angraecinae and twice in Angraecum (S6A Fig). A medium flower size appears to be the ancestral state in Angraecinae, while large and small flowers are derived (S6B Fig). Long spur is the ancestral state and short spur is derived and arose several times independently (S6C Fig). Our results showed that the color (green), the size (small and large), and the spur length (short) of flowers are homoplasic within Angraecum. The taxa that showed uppermost labella appeared to be monophyletic and received very strong support in the phylogeny (Angraecoides, Dolabrifolia, Pectinariella, and Angraecum clades H to M).


Diversification of Angraecum (Orchidaceae, Vandeae) in Madagascar: Revised Phylogeny Reveals Species Accumulation through Time Rather than Rapid Radiation
Ancestral state reconstructions of floral characters in Angraecinae implemented in ‘diversitree’; colors represent character states of the labellum position (uppermost and lowermost) and pie charts represent the probability of ancestral states at nodes. C denotes taxa illustrated in the pictures to the right to represent the flower shape of each clade except for Jumellea which is represented by Jumellea comorensis (not sampled in the phylogeny). Photo: Andriananjamanantsoa.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5036805&req=5

pone.0163194.g005: Ancestral state reconstructions of floral characters in Angraecinae implemented in ‘diversitree’; colors represent character states of the labellum position (uppermost and lowermost) and pie charts represent the probability of ancestral states at nodes. C denotes taxa illustrated in the pictures to the right to represent the flower shape of each clade except for Jumellea which is represented by Jumellea comorensis (not sampled in the phylogeny). Photo: Andriananjamanantsoa.
Mentions: Our results showed that a labellum in the lower position is plesiomorphic in Angraecinae, while an upper labellum is apomorphic and evolved at least five times independently (Fig 5). White flowers appear to be symplesiomorphic in Angraecinae, while green flowers are apomorphic and evolved independently several times in Angraecinae and twice in Angraecum (S6A Fig). A medium flower size appears to be the ancestral state in Angraecinae, while large and small flowers are derived (S6B Fig). Long spur is the ancestral state and short spur is derived and arose several times independently (S6C Fig). Our results showed that the color (green), the size (small and large), and the spur length (short) of flowers are homoplasic within Angraecum. The taxa that showed uppermost labella appeared to be monophyletic and received very strong support in the phylogeny (Angraecoides, Dolabrifolia, Pectinariella, and Angraecum clades H to M).

View Article: PubMed Central - PubMed

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.

No MeSH data available.