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Scientific bulletin n° 327 - September 2009 ew Caledonia is considered as a priority zone of global significance for preservation of biodiversity, owing to the richness of its flora, exceptional in character but threatened. With the aim of achieving better understanding of the evolution of this flora, a phylogenetic study was conducted on one of New Caledonia’s emblematic plant families1, the Cunoniaceae, particularly well adapted to miningaffected soils. DNA sequencing of species of the endemic genus1 Codia enabled IRD researchers and their partners2 to show that more than half of the 13 species of the genus could be interspecific hybrids. Some of them possess new morphological characteristics, absent from the parent species, a finding which emphasizes the crucial role of hybridization in the diversification of these plants. At a time when the Earth’s biodiversity is going through a sixth great extinction, it is important to conserve the processes which lead to the formation of new species. In New Caledonia, this involves the preservation of such situations as contact zones between different soil types, where ecologically different species might co-occur and hybridize. © IRD N Conservation of the natural evolutionary process: a vital factor for New Caledonian biodiversity Spider diagram adapted to show the complex evolution of the genus Codia (Cunoniaceae), endemic to New Caledonia, involving hybridization events. Upper left: C. discolor, Upper right: C. jaffrei, lower left: C. triverticillata, lower right.: C. incrassata The New Caledonia archipelago is considered as a biodiversity hotspot owing to the richness and exceptional character of its fauna and flora, both in its terrestrial and marine environments. Its terrestrial flora amounts to at least 3 300 species with 75 % endemism, meaning the presence of organisms found nowhere else in the world, including five endemic flowering plant families1. This group of islands harbours representatives of numerous ancient lineages, like Amborella, and 13 out of 19 species of Araucaria (column pines), a lineage of conifers abundant during the Mesozoic era, between 251 and 65.5 millions years B.P., the age of the dinosaurs. This diversity is now affected by a range of threats: invasive species, habitat destruction by fire, mining activities (for nickel), global warming, and also urbanization. Now only an estimated 28 % of New Caledonian territory is covered by primary vegetation. To design an effective conservation plan, it is necessary to understand how the plant groups diversified in the course of evolution. An essential step is to integrate several different elements such as vegetation types3, diversity of pollinators or soil types. Such parameters can be studied by using phylogenetic trees, retracing parental relationships between the species. Few studies are available for New Caledonia, unlike flora from other geographical areas such as Hawaii or South Africa. Cunoniaceae, an emblematic family of New Caledonia The Cunoniaceae family gathers together about 300 species of trees and shrubs, divided among 26 genera1, the bulk of them located in the Southern Hemisphere. In New Caledonia, this family is particularly richly represented with 88 species (including Geissois racemosa, the faux-tamanou, and Pancheria brunhesii, known as chêne Institut de recherche pour le développement - 44, boulevard de Dunkerque, CS 90009 F-13572 Marseille Cedex 02 - France - www.ird.fr You can find IRD photos concerning this bulletin, copyright free for press, on www.ird.fr/indigo CONTACTS: Yohan PILLON Former PhD student at the IRD [email protected] Jérôme MUNZINGER Researcher at the IRD [email protected] Laboratoire de Botanique UMR 123 AMAP Address: Centre IRD de Noumea BP A5 – 98848 Noumea cedex New Caledonia REFERENCES: Pillon Y.,Munzinger J., Amir H., Hopkins H.C.F., Chase M.W. Reticulate evolution on a mosaic of soils: diversification of the New Caledonian endemic genus Codia (Cunoniaceae). Molecular Ecology 18 (10), p. 2263–2275, 2009 doi:10.1111/j.1365-294X.2009.04178.x Pillon Y., Hopkins H.C.F., Bradford, J.C. Two new species of Cunonia (Cunoniaceae) from New Caledonia. Kew bulletin 63, p. 419–431, 2008 KEY WORDS: Cunoniaceae, New Caledonia, biodiversity, hybridization rouge), all endemic, divided into seven genera including three endemic ones. The Cunoniaceae live in various types of habitat on the islands and are especially diversified on ultramafic soils, which are rich in iron and magnesium minerals (mining-affected terrain), otherwise scarcely favourable for plant development, owing to the presence of heavy metals (nickel), a high magnesium/ calcium ratio and low availability of water. Importance of hybridization in Cunoniaceae diversification A study of the molecular phylogeny was conducted on Codia, an endemic genus, by IRD researchers and their partners2. The scientists sequenced4 three nuclear genes for each of the 13 species of the genus. More than half of them appear to be the result of natural hybridizations between what are considered as parental species (C. jaffrei, C. nitida, C. incrassata, C. ferruginea). Interspecific hybridization can be a speciation process, meaning it can generate new species. Two plants of hybrid origin have whorled leaves (three leaves arranged around each node) whereas all the parental species have opposite leaves (two leaves per node). The Codia resulting from hybridization can therefore show characteristics the parent species do not have, known as transgressive phenotypes, a sign of the importance of hybridization in morphological diversification of plants. Conserving evolutionary processes like natural hybridization Preservation of the biodiversity, particularly that represented by the appearance of new species which will replace those set to disappear during the current crisis, requires conservation of the processes that favour speciation. In 2008, an IRD scientists and his research partners5 described a new species of Cunoniaceae, Cunonia koghicola, discovered on Mount Koghis, the mountain ridges closest to Noumea. The morphology of this species suggests a hybrid origin. The probable parent species would be Cunonia balansae, a single-leaved species adapted to mining-affected terrain, and Cunonia austrocaledonica, a tree with composite leaves which develops on land untouched by mining. The Mont Koghis Forest covers a geological complex zone where different soil types form a mosaic with a great diversity of vegetation types: mining maquis, niaouli savannah (composed of broad-leaved paper bark, a tree present in New Caledonia and Australia), rainforest on peridotite, serpentine and sedimentary rock formations. Such interfaces provide the opportunity for plants with different ecological requirements to co-exist and hybridize, and should be conserved for their role as a cradle of biodiversity. Mina Vilayleck - DIC Translation - Nicholas FLAY 1. The classification of living organisms is determined according to successive levels of hierarchy: a species belongs to a genus which itself is a member of a family. 2. This research work was conducted jointly with researchers of the University of New Caledonia, Noumea and the Royal Botanic Gardens at Kew in the United Kingdom. 3. A vegetation type denotes a community of plants which manifest a characteristic physical configuration and determines a particular landscape. 4. Sequencing consists of determining the order of DNA nucleotides making up genes. 5.T his study was conducted in partnership with researchers of the Renewable Energy Development Institute at Willits in the USA and the Royal Botanic Gardens at Kew in the United Kingdom. PRESS OFFICE: Vincent Coronini +33 (0)4 91 99 94 87 [email protected] INDIGO, IRD PHOTO LIBRARY : Daina Rechner +33 (0)4 91 99 94 81 [email protected] www.ird.fr/indigo Cunonia koghicola, a species discovered on the Mount Koghis range and described in 2008. © IRD / Yohan Pillon © IRD / Yohan Pillon Scientific bulletin n° 327 - September 2009 For further information Mount Koghis and its ridges, viewed form Noumea. These uplands have a mosaic of soil types favourable for hybridization between plant species. Gaëlle Courcoux, coordinatrice Délégation à l’information et à la communication Tél. : +33 (0)4 91 99 94 90 - fax : +33 (0)4 91 99 92 28 - [email protected]