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

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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.


Posterior probability distributions for the speciation rates (in Ma) of morphological characters using equal rate speciation (μ0 ~ μ1) with the BiSSE model and equal rate extinction (λi ~ λj) with the MuSSE model: flower color (A), labellum position (B), flower size (C), and spur length (D). Abbreviation: v, very.
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pone.0163194.g002: Posterior probability distributions for the speciation rates (in Ma) of morphological characters using equal rate speciation (μ0 ~ μ1) with the BiSSE model and equal rate extinction (λi ~ λj) with the MuSSE model: flower color (A), labellum position (B), flower size (C), and spur length (D). Abbreviation: v, very.

Mentions: Results from BiSSE showed that the second model (μ0 ~ μ1) received the best AIC score for flower color and labellum position (S6 Table). The green and white colors had similar rates of speciation (Fig 2A), while the uppermost labellum showed a higher speciation rate compared to the lowermost one (Fig 2B). Results from MuSSE showed that the third transition model (1 ←2 ←3 ↔ 4) had the best AIC score for flower size, while the full model received the best score for spur length (S6 Table); these models were used to test diversification. The diversification model with extinction rates equal between states received the best score for flower size and spur length, suggesting that character states have an effect on speciation. Large flowers showed higher speciation rates compared to small, medium and very large flowers (Fig 2C). All spur length states had a similar effect on speciation rates (Fig 2D).


Diversification of Angraecum (Orchidaceae, Vandeae) in Madagascar: Revised Phylogeny Reveals Species Accumulation through Time Rather than Rapid Radiation
Posterior probability distributions for the speciation rates (in Ma) of morphological characters using equal rate speciation (μ0 ~ μ1) with the BiSSE model and equal rate extinction (λi ~ λj) with the MuSSE model: flower color (A), labellum position (B), flower size (C), and spur length (D). Abbreviation: v, very.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0163194.g002: Posterior probability distributions for the speciation rates (in Ma) of morphological characters using equal rate speciation (μ0 ~ μ1) with the BiSSE model and equal rate extinction (λi ~ λj) with the MuSSE model: flower color (A), labellum position (B), flower size (C), and spur length (D). Abbreviation: v, very.
Mentions: Results from BiSSE showed that the second model (μ0 ~ μ1) received the best AIC score for flower color and labellum position (S6 Table). The green and white colors had similar rates of speciation (Fig 2A), while the uppermost labellum showed a higher speciation rate compared to the lowermost one (Fig 2B). Results from MuSSE showed that the third transition model (1 ←2 ←3 ↔ 4) had the best AIC score for flower size, while the full model received the best score for spur length (S6 Table); these models were used to test diversification. The diversification model with extinction rates equal between states received the best score for flower size and spur length, suggesting that character states have an effect on speciation. Large flowers showed higher speciation rates compared to small, medium and very large flowers (Fig 2C). All spur length states had a similar effect on speciation rates (Fig 2D).

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.