Abstract
Despite the general belief that the interaction between extrafloral nectaries (EFNs) and ants is mutualistic, the defensive function of EFNs has been poorly documented in South American savannas. In this article, we evaluate the potential impact of EFNs (benefits and costs) on two species of plants from the dry areas of Central Brazil, Anemopaegma album and Anemopaegma scabriusculum (Bignoniaceae). In particular, we characterize the composition of substances secreted by the EFNs, test whether EFNs attract ants, and whether ants actually present a defensive role, leading to reduced herbivory and increased plant fitness. Histochemical analyses indicated that EFNs from both species of Anemopaegma secrete an exudate that is composed of sugars, and potentially lipids and proteins. Furthermore, EFNs from both species were shown to present a significant role in ant attraction. However, contrary to common expectations, ants were not found to protect plants against herbivore attack. No effect was found between ant visitation and flower or fruit production in A. album, while the presence of ants led to a significant decrease in flower production in A. scabriusculum. These results suggest that EFNs might present a similar cost and benefit in A. album, and a higher cost than benefit in A. scabriusculum. Since the ancestor of Anemopaegma occupied humid forests and already presented EFNs that were maintained in subsequent lineages that occupied savannas, we suggest that phylogenetic inertia might explain the presence of EFNs in the species of Anemopaegma in which EFNs lack a defensive function.
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Acknowledgments
This article is part of the doctoral thesis of A. Nogueira. Funding came from the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP 2007/55433-8 and Grant 2007/54917-1), and logistic support from IB-USP, IB-UNESP, IEF-MG (Gerência de Projetos e Pesquisas, Diretoria de Biodiversidade), and the State Park of Grão Mogol-MG. We are gratefully to all the assistance provided during field-work, especially to Patrícia Falcão Bueno. We thank R. Feitosa for the identification of ants and L. Borowiec (Coleoptera), U. R. Martins (Coleoptera), and F. Domenico (Orthoptera) for the identification of herbivores. We also thank to Paul Fine, Fabrício Baccaro, Miriam Kaehler, Pedro J. Rey, and one anonymous reviewer for fruitful discussions and comments on this article.
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Nogueira, A., Guimarães, E., Machado, S.R. et al. Do extrafloral nectaries present a defensive role against herbivores in two species of the family Bignoniaceae in a Neotropical savannas?. Plant Ecol 213, 289–301 (2012). https://doi.org/10.1007/s11258-011-9974-3
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DOI: https://doi.org/10.1007/s11258-011-9974-3