Recently evolved diversity and convergent radiations of rainforest mahoganies (Meliaceae) shed new light on the origins of rainforest hyperdiversity.

Tropical rainforest hyperdiversity is often suggested to have evolved over a long time-span (the 'museum' model), but there is also evidence for recent rainforest radiations. The mahoganies (Meliaceae) are a prominent plant group in lowland tropical rainforests world-wide but also occur in all other tropical ecosystems. We investigated whether rainforest diversity in Meliaceae has accumulated over a long time or has more recently evolved. We inferred the largest time-calibrated phylogeny for the family to date, reconstructed ancestral states for habitat and deciduousness, estimated diversification rates and modeled potential shifts in macro-evolutionary processes using a recently developed Bayesian method. The ancestral Meliaceae is reconstructed as a deciduous species that inhabited seasonal habitats. Rainforest clades have diversified from the Late Oligocene or Early Miocene onwards. Two contemporaneous Amazonian clades have converged on similar ecologies and high speciation rates. Most species-level diversity of Meliaceae in rainforest is recent. Other studies have found steady accumulation of lineages, but the large majority of plant species diversity in rainforests is recent, suggesting (episodic) species turnover. Rainforest hyperdiversity may best be explained by recent radiations from a large stock of higher level taxa.

Niche evolution through time and across continents: The story of Neotropical Cedrela (Meliaceae).

PREMISE OF THE STUDY: Climatic and geological changes have been considered as major drivers of biological diversification. However, it has been generally assumed that lineages retain common environmental affinities, suggesting a limited capacity to switch their climatic niche. We tested this assumption with a study of the evolution of climatic niches in the Neotropical tree genus Cedrela (Meliaceae). • METHODS: We combined distribution models of extant Cedrela with a dated molecular phylogeny based on one nuclear (ITS) and three plastid markers (psbA-trnH, trnS-G and psbB-T-N) to reconstruct the evolutionary dynamics of climatic niches. We calculated relative disparity of climatic tolerances over time to test for niche evolution within subclades or divergence between subclades and conservatism among closely related groups. Published fossil records and studies on paleosols were evaluated for the distribution and climatic conditions of extinct Cedrela. • KEY RESULTS: The fossil record of Cedrela suggested a major biome shift from paratropical conditions into warm-temperate seasonal climates in the Early Oligocene of western North America. In the Miocene, Cedrela extended from North America (John Day Formation, Oregon, USA) to southern Central America (Gatún, Panama). Diversification in the early evolutionary history was mainly driven by changes in precipitation. Temperature had an increasing impact on ecological diversification of the genus from the Miocene onwards. Sister-species comparisons revealed that recent speciation events may be related to divergence of climatic tolerances. • CONCLUSIONS: Our study highlights the complexity of climatic niche dynamics, and shows how conservatism and evolution have acted on different temporal scales and climatic parameters in Cedrela.

Biogeography of cedrela (meliaceae, sapindales) in central and South america.

Dated phylogenies have helped clarify the complex history of many plant families that today are restricted to the world's tropical forests, but that have Eocene, Oligocene, and Miocene fossils from the northern hemisphere. One such family is the Meliaceae. Here we infer the history of the neotropical Meliaceae genus Cedrela (17 species), the sister clade of which today is restricted to tropical Asia. Sequences from the nuclear ribosomal spacer region and five plastid loci obtained for all ingroup species and relevant outgroups were used to infer species relationships and for molecular-clock dating under two Bayesian relaxed clock models. The clock models differed in their handling of rate autocorrelation and sets of fossil constraints. Results suggest that (1) crown group diversification in Cedrela started in the Oligocene/Early Miocene and intensified in the Late Miocene and Early Pliocene, and (2) Central American Cedrela species do not form a clade, implying reentry into Central America after the closure of the Panamanian Isthmus. At present, Cedrela is distributed in both dry and humid habitats, but morphological features suggest an origin in dry forest under seasonal climates, fitting with Miocene and Pliocene Cedrela fossils from deciduous forests.

Molecular phylogenetics of Neotropical Cedreleae (mahogany family, Meliaceae) based on nuclear and plastid DNA sequences reveal multiple origins of "Cedrela odorata".

This study focuses on the 17 Neotropical species described in Cedrela (Meliaceae; Cedreleae), in particular C. odorata, which has been shown in past population genetic studies to be more variable than other tree species. We sampled two sets of molecular markers, nuclear ribosomal spacers (nrITS), and several plastid regions (the psbB, psbN, psbT exons and the trnS-trnG spacer). Both sets of markers produced congruent results using parsimony, maximum likelihood and Bayesian methods for a set of taxa that include outgroups (outside Cedreleae) as well as other members of the related genera within Cedreleae. All results confirm current delimitation of Cedreleae and genetic distinctiveness for four new species with divergent morphologies. Our study also provides evidence that there are several genetic entities among the accessions of C. odorata that have distinct ranges or habitat preferences. These entities may constitute new species, are morphologically cryptic and require a great deal more investigation to delimit their ranges. Our results have important implications for conservation of Cedrela odorata, which is heavily harvested throughout its range in the American tropics.

Molecular phylogenetics of Meliaceae (Sapindales) based on nuclear and plastid DNA sequences.

Phylogenetic analyses of Meliaceae, including representatives of all four currently recognized subfamilies and all but two tribes (32 genera and 35 species, respectively), were carried out using DNA sequence data from three regions: plastid genes rbcL, matK (partial), and nuclear 26S rDNA (partial). Individual and combined phylogenetic analyses were performed for the rbcL, matK, and 26S rDNA data sets. Although the percentage of informative characters is highest in the segment of matK sequenced, rbcL provides the greatest number of informative characters of the three regions, resulting in the best resolved trees. Results of parsimony analyses support the recognition of only two subfamilies (Melioideae and Swietenioideae), which are sister groups. Melieae are the only tribe recognized previously that are strongly supported as monophyletic. The members of the two small monogeneric subfamilies, Quivisianthe and Capuronianthus, fall within Melioideae and Swietenioideae, respectively, supporting their taxonomic inclusion in these groups. Furthermore, the data indicate a close relationship between Aglaieae and Guareeae and a possible monophyletic origin of Cedreleae of Swietenioideae. For Trichilieae (Melioideae) and Swietenieae (Swietenioideae) lack of monophyly is indicated.

Mahogany carving a future.

Mahogany (Swietenia marcophylla is widely regarded by conservationists as on the verge of extinction. However, throughout most of its range, it is generally regenerating well within virgin and logged forest, and is a good colonizer of abandoned farm land. It thrives on disturbance and, outside its natural range, is a good plantation tree.