AOBPreview originally published online on August 31, 2006
Annals of Botany 2006 98(5):1061-1072; doi:10.1093/aob/mcl190
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Extensive Clonality and Strong Differentiation in the Insular Pacific Tree Santalum insulare: Implications for its Conservation
1 CIRAD, Forestry Department, Research Unit 39 ‘Genetic Diversity and Breeding of Forest Tree Species’ Campus International de Baillarguet TA 10/C, 34398 Montpellier Cedex 5, France
2 Laboratory of Natural Products Chemistry, University of French Polynesia BP6570-98702 Faa'a, Tahiti, French Polynesia
* For correspondence. E-mail jean-marc.bouvet{at}cirad.fr
Received: 13 April 2006 Returned for revision: 8 June 2006 Accepted: 24 July 2006 Published electronically: 31 August 2006
• Background and Aims The impact of evolutionary forces on insular systems is particularly exacerbated by the remoteness of islands, strong founder effects, small population size and the influence of biotic and abiotic factors. Patterns of molecular diversity were analysed in an island system with Santalum insulare, a sandalwood species endemic to eastern Polynesia. The aims were to evaluate clonality and to study the genetic diversity and structure of this species, in order to understand the evolutionary process and to define a conservation strategy.
• Methods Eight nuclear microsatellites were used to investigate clonality, genetic variation and structure of the French Polynesian sandalwood populations found on ten islands distributed over three archipelagos.
• Key Results It was found that 58 % of the 384 trees analysed were clones. The real size of the populations is thus dramatically reduced, with sometimes only one genet producing ramets by root suckering. The diversity parameters were low for islands (nA = 1·5–5·0; HE = 0·28–0·49). No departure from Hardy–Weinberg proportion was observed except within Tahiti island, where a significant excess of homozygotes was noted in the highland population. Genetic structure was characterized by high levels of differentiation between archipelagos (27 % of the total variation) and islands (FST = 0·50). The neighbour-joining tree did not discriminate the three archipelagos but separated the Society archipelago from the other two.
• Conclusions This study shows that clonality is a frequent phenomenon in S. insulare. The genetic diversity within populations is lower than the values assessed in species distributed on the mainland, as a consequence of insularity. But this can also be explained by the overexploitation of sandalwood. The differentiation between archipelagos and islands within archipelagos is very high because of the limited gene flow due to oceanic barriers. Delineation of evolutionary significant units and principles for population management are proposed based on this molecular analysis.
Key words: Clonality, conservation, endangered species, genetic diversity, genetic structure, insularity, nuclear microsatellites, Santalum insulare, French Polynesia