AOBPreview originally published online on September 22, 2009
Annals of Botany 2009 104(6):1231-1242; doi:10.1093/aob/mcp231
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Small effect of fragmentation on the genetic diversity of Dalbergia monticola, an endangered tree species of the eastern forest of Madagascar, detected by chloroplast and nuclear microsatellites
1 Silo national des Graines Forestières, Ambatobe BP 5091, Antananarivo, Madagascar
2 Cirad-Bios Department, Research Unit ‘genetic diversity and breeding of forest tree species’, Campus international de Baillarguet TA-A 39/C, BP 5035, 34398 Montpellier cedex, France
* For correspondence. E-mail jean-marc.bouvet{at}cirad.fr
Received: 17 May 2009 Returned for revision: 29 June 2009 Accepted: 27 July 2009 Published electronically: 22 September 2009
Background and Aims: The oriental forest ecosystem in Madagascar has been seriously impacted by fragmentation. The pattern of genetic diversity was analysed on a tree species, Dalbergia monticola, which plays an important economic role in Madagascar and is one of the many endangered tree species in the eastern forest.
Methods: Leaves from 546 individuals belonging to 18 small populations affected by different levels of fragmentation were genotyped using eight nuclear (nuc) and three chloroplast (cp) microsatellite markers.
Key Results: For nuclear microsatellites, allelic richness (R) and heterozygosity (He,nuc) differed between types of forest: R = 7·36 and R = 9·55, He,nuc = 0·64 and He,nuc = 0·80 in fragmented and non-fragmented forest, respectively, but the differences were not significant. Only the mean number of alleles (Na,nuc) and the fixation index FIS differed significantly: Na,nuc = 9·41 and Na,nuc = 13·18, FIS = 0·06 and FIS = 0·15 in fragmented and non-fragmented forests, respectively. For chloroplast microsatellites, estimated genetic diversity was higher in non-fragmented forest, but the difference was not significant. No recent bottleneck effect was detected for either population. Overall differentiation was low for nuclear microsatellites (FST,nuc = 0·08) and moderate for chloroplast microsatellites (FST,cp = 0·49). A clear relationship was observed between genetic and geographic distance (r = 0·42 P < 0·01 and r = 0·42 P = 0·03 for nuclear and chloroplast microsatellites, respectively), suggesting a pattern of isolation by distance. Analysis of population structure using the neighbor-joining method or Bayesian models separated southern populations from central and northern populations with nuclear microsatellites, and grouped the population according to regions with chloroplast microsatellites, but did not separate the fragmented populations.
Conclusions: Residual diversity and genetic structure of populations of D. monticola in Madagascar suggest a limited impact of fragmentation on molecular genetic parameters.
Key words: Dalbergia monticola, genetic structure, fixation index, bottleneck, molecular markers, Bayesian methods, Madagascar
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