Multiple colonizations from Madagascar and converged acquisition of dioecy in the Mascarene Dombeyoideae (Malvaceae) as inferred from chloroplast and nuclear DNA sequence analyses

Background and Aims

In the Mascarenes, a young oceanic archipelago composed of three main islands, the Dombeyoideae (Malvaceae) have diversified extensively with a high endemism rate. With the exception of the genus Trochetia, Mascarene Dombeyoideae are described as dioecious whereas Malagasy and African species are considered to be monocline, species with individuals bearing hermaphrodite/perfect flowers. In this study, the phylogenetic relationships were reconstructed to clarify the taxonomy, understand the phylogeographic pattern of relationships and infer the evolution of the breeding systems for the Mascarenes Dombeyoideae.

Methods

Parsimony and Bayesian analysis of four DNA markers (ITS, rpl16 intron and two intergenic spacers trnQ-rsp16 and psbM-trnD) was used. The molecular matrix comprised 2985 characters and 48 taxa. The Bayesian phylogeny was used to infer phylogeographical hypotheses and the evolution of breeding systems.

Key Results

Parsimony and Bayesian trees produced similar results. The Dombeyoideae from the Mascarenes are polyphyletic and distributed among four clades. Species of Dombeya, Trochetia and Ruizia are nested in the same clade, which implies the paraphyly of Dombeya. Additionally, it is shown that each of the four clades has an independent Malagasy origin. Two adaptive radiation events have occurred within two endemic lineages of the Mascarenes. The polyphyly of the Mascarene Dombeyoideae suggests at least three independent acquisitions of dioecy.

Conclusions

This molecular phylogeny highlights the taxonomic issues within the Dombeyoideae. Indeed, the limits and distinctions of the genera Dombeya, Trochetia and Ruizia should be reconsidered. The close phylogeographic relationships between the flora of the Mascarenes and Madagascar are confirmed. Despite their independent origins and a distinct evolutionary history, each endemic clade has developed a different breeding systems (dioecy) compared with the Malagasy Dombeyoideae. Sex separation appears as an evolutionary convergence and may be the consequence of selective pressures particular to insular environments.     

Molecular phylogenetics of Sarcolaenaceae (Malvales), Madagascar's largest endemic plant family

With 72 species belonging to ten genera, Sarcolaenaceae are the largest and most diverse of Madagascar's endemic plant families. Comprising shrubs and trees, with members found in nearly all of this island nation's biogeographic regions, they are characterised by the presence of a distinctive extra‐floral involucre that is more or less accrescent, partially or completely covering or enveloping the fruit. We present the first molecular phylogenetic study of Sarcolaenaceae, using broad sampling that encompasses the family's taxonomic and morphological diversity, including 46 species representing all ten genera and sequence data from one nuclear marker (ITS) and three plastid regions (psaA‐ORF170, psbA‐trnH and rbcL), to reconstruct phylogenetic relationships using Bayesian inference and maximum likelihood. Results confirm the monophyly of Sarcolaenaceae and of eight of the ten genera; the monophyly of Rhodolaena remains ambiguous, although the taxa sampled were recovered in two well supported clades that are coherent in terms of morphology and geography. Only a single species of Eremolaena was available for study. The phylogenetic backbone of Sarcolaenaceae is not fully resolved, making it difficult to identify potential morphological synapomorphies or ecological preferences between and within genera. In the family, two monophyletic groups were, however, found [Pentachlaena + Eremolaena + Perrierodendron (Clade A) and Xyloolaena + Leptolaena + Sarcolaena + Mediusella + Xerochlamys (Clade B)] that are consistent with previous results based on morphology. Expanded species sampling and data from additional, more quickly evolving markers will be needed to produce a fully resolved phylogenetic tree for Sarcolaenaceae, which could then serve as a basis for exploring macroevolutionary patterns and processes in this remarkable family and reconstructing its biogeographic history.     

High evolutionary and functional distinctiveness of endemic monocots in world islands

Functionally and evolutionarily distinct species have traits or an evolutionary history that are shared by few others in a given set, which make them priority species for biodiversity conservation. On islands, life in isolation has led to the evolution of many distinct forms and functions as well as to a high level of endemism. The aim of this study is to assess the evolutionary and functional distinctiveness of insular monocotyledons and their distribution across 126 islands worldwide. We show that evolutionary and functional distinctiveness are decoupled but that both are higher on islands than on continental areas. Anagenesis on islands followed by extinctions and/or diversification on the mainland may have led to highly evolutionarily distinct species while functionally distinct species may have arisen from ecological niche shift or niche expansion. Insular endemic species with high evolutionary distinctiveness but not with high functional distinctiveness are significantly range-restricted compared to less distinct species, possibly indicating differences in dispersal potential. By showing that distinctiveness is high on islands and that the most distinct species are range-restricted, our study has important conservation implications. Indeed, islands are among the most threatened systems of the world, and extinctions of the most distinct species could lead to significant loss of phylogenetic and functional diversity.

     

DNA barcoding in a biodiversity hot spot: potential value for the identification of Malagasy Euphorbia L. listed in CITES Appendices I and II

The island of Madagascar is a key hot spot for the genus Euphorbia, with at least 170 native species, almost all endemic. Threatened by habitat loss and illegal collection of wild plants, nearly all Malagasy Euphorbia are listed in CITES Appendices I and II. The absence of a reliable taxonomic revision makes it particularly difficult to identify these plants, even when fertile, and thereby compromises the application of CITES regulations. DNA barcoding, which can facilitate species‐level identification irrespective of developmental stage and the presence of flowers or fruits, may be a promising tool for monitoring and controlling trade involving threatened species. In this study, we test the potential value of barcoding on 41 Euphorbia species representative of the genus in Madagascar, using the two widely adopted core barcode markers (matK and rbcL), along with two additional DNA regions, nuclear internal transcribed spacer (ITS) and the chloroplastic intergenic spacer psbA‐trnH. For each marker and for selected marker combinations, inter‐ and intraspecific distance estimates and species discrimination rates are calculated. Results using just the ‘official’ barcoding markers yield overlapping inter‐ and intraspecific ranges and species discrimination rates below 60%. When ITS is used, whether alone or in combination with the core markers, species discrimination increases to nearly 100%, whereas the addition of psbA‐trnH produces less satisfactory results. This study, the first ever to test barcoding on the large, commercially important genus Euphorbia shows that this method could be developed into a powerful identification tool and thereby contribute to more effective application of CITES regulations.     

Rethinking the links between systematic studies and ex situ living collections as a contribution to the Global Strategy for Plant Conservation

The Muséum national d’histoire naturelle (MNHN) in Paris holds ca. 70 million specimens. The collections were in need of a strategy to ensure their long-term conservation. We discuss how the Department of Botanical and Zoological Gardens (DJBZ; tropical living collections), and the Department of Systematics and Evolution (DSE; herbarium) contribute to achieving GSPC’s Target 1 (‘a widely accessible working list of known plant species as a step towards a complete world flora’). The DJBZ started encouraging better management of the collections, evolving towards focused reference collections, where all specimens have well-documented collection data. The objective is to link all collections to a scientific referee. This has already been achieved for a number of taxa. The herbarium of the DSE (acronym P) is among the world’s largest (11 million specimens, including 400,000 types). The collection’s heterogeneity impedes access to its data, since P is a mix of recent well-documented collections and historical collections at various curational levels. P is currently under renovation, which started by mounting all ca. 2 million unmounted specimens. The project also includes databasing and imaging of every specimen. The database now holds around 1,000,000 records. For taxonomic studies, living collections are crucial, especially for plants that are not easily preserved as herbarium specimens. Living collections also enable studies impossible to forecast at the time of collecting. Herbaria and living collections should therefore be conceived as interoperable entities requiring common scientific curation. Through a combination of its assets and the expertise of its researchers, the MNHN is well prepared to tackle the new objectives of the GSPC beyond 2010.