AOBPreview originally published online on January 19, 2006
Annals of Botany 2006 97(3):389-403; doi:10.1093/aob/mcj052
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Allozyme Diversity and Morphometrics of Melocactus paucispinus (Cactaceae) and Evidence for Hybridization with M. concinnus in the Chapada Diamantina, North-eastern Brazil
1 Universidade Estadual de Feira de Santana, Departamento de Ciências Biológicas, Laboratório de Sistemática Molecular de Plantas, Rodovia BR 116, Km 03, Feira de Santana, Bahia, CEP 44·130-460, Brazil 2 Universidade Federal de Minas Gerais, Instituto de Ciências Biológicas, Departamento de Botânica, Laboratório de Sistemática, Av. Antônio Carlos, 6627, Pampulha, Belo Horizonte, Minas Gerais, 31270-901, Brazil 3 Universität Zürich, Institut für Systematische Botanik, Zollikerstrasse 107, CH-8008 Zürich, Switzerland and 4 Universidade Estadual de Campinas, Instituto de Biologia, Departamento de Genética e Evolução, Laboratório de Diversidade Genética, Campinas, São Paulo, 13083-970, Brazil
* For correspondence. E-mail sabrina.lambert{at}bol.com.br; borba{at}gmx.net
Received: 28 April 2005 Returned for revision: 26 September 2005 Accepted: 23 November 2005 Published electronically: 19 January 2006
• Background and Aims Melocacatus paucispinus (Cactaceae) is endemic to the state of Bahia, Brazil, and due to its rarity and desirability to collectors it has been considered threatened with extinction. This species is usually sympatric and inter-fertile with M. concinnus, and morphological evidence for hybridization between them is present in some populations. Levels of genetic and morphological variation and sub-structuring in populations of these species were assessed and an attempt was made to verify the occurrence of natural hybridization between them.
• Methods Genetic variability was surveyed using allozymes (12 loci) and morphological variability using multivariate morphometric analyses (17 vegetative characters) in ten populations of M. paucispinus and three of M. concinnus occurring in the Chapada Diamantina, Bahia.
• Key Results Genetic variability was low in both species (P = 0·0–33·3, A = 1·0–1·6, He = 0·000–0·123 in M. paucispinus; P = 0·0–25·0, A = 1·0–1·4, He = 0·000–0·104 in M. concinnus). Deficit of heterozygotes within the populations was detected in both species, with high values of FIS (0·732 and 0·901 in M. paucispinus and M. concinnus, respectively). Evidence of hybridization was detected by the relative allele frequency in the two diaphorase loci. High levels of genetic (FST = 0·504 in M. paucispinus and 0·349 in M. concinnus) and morphological (A = 0·20 in M. paucispinus and 0·17 in M. concinnus) structuring among populations were found.
• Conclusions The Melocactus spp. displayed levels of genetic variability lower than the values reported for other cactus species. The evidence indicates the occurrence of introgression in both species at two sites. The high FST values cannot be explained by geographical substructuring, but are consistent with hybridization. Conversely, morphological differentiation in M. paucispinus, but not in M. concinnus, is probably due to isolation by distance.
Key words: Allozymes, Cactaceae, campo rupestre, Chapada Diamantina, genetic diversity, Melocactus concinnus, Melocactus paucispinus, morphological variability, morphometrics
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