Species richness in the tropics has been attributed to the gradual accumulation of species over a long geological period in stable equatorial climates or, conversely, to speciation in response to late Tertiary geological events and unstable Pleistocene climates. DNA sequence data are consistent with recent diversification in Inga, a species-rich neotropical tree genus. We estimate that speciation was concentrated in the past 10 million years, with many species arising as recently as 2 million years ago. This coincides with the more recent major uplifts of the Andes, the bridging of the Isthmus of Panama, and Quaternary glacial cycles. Inga may be representative of other species-rich neotropical genera with rapid growth and reproduction, which contribute substantially to species numbers in the world's most diverse flora.

SummaryTropical 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.

No abstract

Abstract. Ecological surveys of tropical tree communities have provided an important source of data to study the forces that generate and maintain tropical diversity. Accurate species identification is central to these studies. Incorrect lumping or splitting of species will distort results, which may in turn affect conclusions. Although ecologists often work with taxonomists, they likely make some identification errors. This is because most trees encountered in the field are not reproductive and must be identified using vegetative characters, while most species descriptions rely on fruit and flower characters. Because every tree has DNA, ecological surveys can incorporate molecular approaches to enhance accuracy. This study reports an extensive ecological and molecular survey of nearly 4000 trees belonging to 55 species in the tree genus Inga (Fabaceae). These trees were sampled in 25 community surveys in the southwestern Amazon. In a process of reciprocal illumination, trees were first identified to species using vegetative characters, and these identifications were revised using phylogenies derived from nuclear and chloroplast DNA sequences.We next evaluated the effects of these revised species counts upon analyses often used to assess ecological neutral theory. The most common morphological identification errors involved incorrectly splitting rare morphological variants of common species and incorrectly lumping geographically segregated, morphologically similar species. Total error rates were significant (6.8-7.6% of all individuals) and had a measurable impact on ecological analyses. The revised identifications increased support for spatially autocorrelated, potentially neutral factors in determining community composition. Nevertheless, the general conclusions of community-level ecological analyses were robust to misidentifications. Ecological factors, such as soil composition, and potentially neutral factors, such as dispersal limitation, both play important roles in the assembly of Inga communities. In contrast, species-level analyses of neutrality with respect to habitat were strongly impacted by identification errors. Although this study found errors in morphological identifications, there was also strong evidence that a purely molecular approach to species identification, such as DNA barcoding, would be prone to substantial errors. The greatest accuracy in ecological surveys will be obtained through a synthesis of traditional, morphological and modern, molecular approaches.

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.

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.

No abstract

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.