AOBPreview originally published online on March 1, 2007
Annals of Botany 2007 99(4):625-635; doi:10.1093/aob/mcm012
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Post-zygotic Reproductive Isolation Between Sympatric Taxa in the Chamaecrista desvauxii Complex (Leguminosae–Caesalpinioideae)
1 Universidade Estadual de Feira de Santana, Departamento de Ciências Biológicas, Laboratório de Sistemática Molecular de Plantas, Rodovia BR116 Km 03, Feira de Santana, BA, 44031-460, Brazil
2 Universidade Federal de Minas Gerais, Instituto de Ciências Biológicas, Departamento de Botânica, Avenida Antônio Carlos 6627, Caixa Postal 486, Belo Horizonte, MG, 31270-901, Brazil
* For correspondence. E-mail crisbotanica{at}yahoo.com.br
Received: 19 October 2006 Returned for revision: 20 November 2006 Accepted: 3 January 2007 Published electronically: 1 March 2007
Background and Aims: Differences in the mating systems and the mechanisms of reproductive isolation between Chamaecrista desvauxii var. graminea and C. desvauxii var. latistipula were examined in the Chapada Diamantina, Brazil. These taxa occur sympatrically, and their populations demonstrate marked morphological differences. The objective of the present work was to determine if reproductive isolation mechanisms exist between these two populations of C. desvauxii, and to determine the influence of these putative mechanisms on their genetic differentiation.
Methods: Field observations were made of floral biology, phenology and floral visitation, and experiments on intra- and interpopulation pollination and germination rates of the resultant seeds were performed. A genetic examination of the populations was undertaken using four allozyme loci.
Key Results: The varieties examined demonstrated overlapping of flowering periods during the months of June to September. The main pollinator for both varieties was the bee Bombus brevivillus. Both varieties are self-compatible, and a large number of fruits are formed in cross-pollinations with high seed germination rates. Inter-taxa pollinations result in high levels of fruit production, but no seeds are formed. Two of the four loci examined were diagnostic for the varieties, and exclusive high-frequency alleles were encountered at the other loci, leading to a high genetic distance between the two populations (0·495).
Conclusions: Pre-zygotic barriers were not found between the two varieties, and these remain isolated due to post-zygotic events. The two varieties demonstrate marked differences in their morphology, floral biology, phenology and genetic make-up, all of which indicate that they should be treated as two distinct species. A complete revision involving the other varieties of the C. desvauxii complex will be necessary in order to define these two taxa formally.
Key words: Allozyme, campo rupestre, Chamaecrista desvauxii, Chapada Diamantina, floral biology, Leguminosae, mating systems, pollination, post-zygotic barriers, reproductive isolation, sympatric species
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