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AOBPreview originally published online on September 28, 2006
Annals of Botany 2006 98(6):1207-1213; doi:10.1093/aob/mcl202
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© The Author 2006. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Low Genetic Structure in an Epiphytic Orchidaceae (Oncidium hookeri) in the Atlantic Rainforest of South-eastern Brazil

SUZANA ALCANTARA1,*, JOÃO SEMIR2 and VERA NISAKA SOLFERINI1

1 Departamento de Genética e Evolução, Instituto de Biologia, Universidade Estadual de Campinas Caixa Postal 6109, Campinas, SP, 13083-970, Brazil
2 Departamento de Botânica, Instituto de Biologia, Universidade Estadual de Campinas Caixa Postal 6109, Campinas, SP, 13083-970, Brazil

*For correspondence. E-mail suzanaalcantara{at}yahoo.com.br

Received: 10 May 2006    Returned for revision: 5 July 2006    Accepted: 7 August 2006    Published electronically: 28 September 2006

• Background and Aims Oncidium hookeri is a neotropical species of epiphytic Orchidaceae found in the Brazilian Atlantic rainforest at the top of the Mantiqueira Range of mountains. The genetic variation of O. hookeri was studied to assess the distribution of genetic variability within and among six populations localized in Atlantic rainforest remnants. Gene flow among populations and the occurrence of recent bottlenecks were investigated in order to infer the degree of isolation of these populations.

• Methods Thirteen polymorphic loci were used for allozyme electrophoresis. The data were analysed by means of standard statistical approaches, to estimate gene diversity and the genetic structure of the populations.

• Key Results The mean gene diversity and allelic richness were He = 0·099 and A = 1·75, respectively. F-statistics revealed high heterozygote deficiencies in all populations (FIS = 0·43–0·82). Several rare alleles were found in all the populations, and three populations presented private alleles. Low genetic differentiation among O. hookeri populations was detected (FST = 0·029); natural selection may be involved in PGM locus differentiation among populations. The genetic differentiation between paired populations was low, bearing no correlation with geographic distance (Mantel test: r = –0·34, P = 0·72). Only two populations showed signs of recent bottlenecks.

• Conclusions The heterozygote deficiency found seems to be caused by pollinator behaviour; the low frequencies of several alleles of different loci can be maintained due to clonal propagation. Despite the stochastic nature of the wind-dispersal of seeds to long distances, this process may promote an effective gene flow among populations, thus avoiding genetic differentiation.

Key words: Orchidaceae, Oncidium hookeri, allozyme, genetic variability, genetic structure, tropical Atlantic rainforest, wind-dispersed seeds, vegetative propagation, insect-pollination


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