AOBPreview originally published online on August 19, 2004
Annals of Botany 2004 94(4):545-551; doi:10.1093/aob/mch171
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Annals of Botany 94/4, © Annals of Botany Company 2004; all rights reserved
Diversity and Genetic Structure of the Mexican Endemic Epiphyte Tillandsia achyrostachys E. Morr. ex Baker var. achyrostachys (Bromeliaceae)
1 Laboratorio de Genética de Poblaciones, Departamento de Biología Evolutiva, Instituto de Ecología, A. C. Km 2·5 Antigua Carretera a Coatepec, Xalapa 91070, Veracruz, México and 2 CEAMISH-UAEM, Av. Universidad 1001, Col. Chamilpa, Cuernavaca, Morelos, México
* For correspondence. E-mail astorga{at}ecologia.edu.mx
Received: 9 April 2004 Returned for revision: 15 June 2004 Accepted: 18 June 2004 Published electronically: 19 August 2004
• Background and Aims The monoecious, bird-pollinated epiphytic Tillandsia achyrostachys E. Morr. ex Baker var. achyrostachys is an endemic bromeliad of the tropical dry forests of Mexico with clonal growth. In the Sierra de Huautla Natural Reserve this species shows a host preference for Bursera copallifera (Sessé & Moc ex. DC) Bullock. As a result of deforestation in the study area, B. copallifera has become a rare tree species in the remaining forest patches. This human-induced disturbance has directly affected the population densities of T. achyrostachys. In this study the genetic consequences of habitat fragmentation were assessed by comparing the genetic diversity, gene flow and genetic differentiation in six populations of T. achyrostachys in the Sierra de Huautla Natural Reserve, Mexico.
• Methods Allozyme electrophoresis of sixteen loci (eleven polymorphic and five monomorphic) were used. The data were analysed with standard statistical approximations for obtaining diversity, genetic structure and gene flow.
• Key Results Genetic diversity and allelic richness were: HE = 0·21 ± 0·02, A = 1·86 ± 0·08, respectively. F-statistics revealed a deficiency of heterozygous plants in all populations (Fit = 0·65 ± 0·02 and Fis = 0·43 ± 0·06). Significant genetic differentiation between populations was detected (Fst = 0·39 ± 0·07). Average gene flow between pairs of populations was relatively low and had high variation (Nm = 0·46 ± 0·21), which denotes a pattern of isolation by distance. The genetic structure of populations of T. achyrostachys suggests that habitat fragmentation has reduced allelic richness and genetic diversity, and increased significant genetic differentiation (by approx. 40 %) between populations.
• Conclusions The F-statistic values (>0) and the level of gene flow found suggest that habitat fragmentation has broken up the former population structure. In this context, it is proposed that the host trees of T. achyrostachys should be considered as a conservation priority, since they represent the limiting factor to bromeliad population growth and connectivity.
Key words: Allozymic electrophoresis, bromeliad, conservation genetics, genetic structure, gene flow, habitat fragmentation, tropical dry forest, Sierra de Huautla Natural Reserve Mexico
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