O papel de associação entre formigas e nectários extranupciais sobre o êxito reprodutivo de Tocoyena formosa (Rubiaceae)
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Data
2017-02-24
Autores
Izquierdo, Juliana Verónica [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
As plantas oferecem recurso alimentar a muitas espécies animais através de diferentes estruturas. Dentre tais estruturas estão os nectários, que são glândulas multicelulares especializadas na produção e secreção de néctar. Estes nectários podem ocorrer tanto em partes reprodutivas como vegetativas, e podem ser florais ou extraflorais. Entretanto, também podem ser classificados quanto a sua função em relação com a polinização, sendo do tipo nupcial (quando sua função está relacionada à polinização) ou extranupcial (quando sua função está relacionada à defesa). Tocoyena formosa (Rubiaceae) é uma espécie comum do Cerrado, cujos nectários extraflorais são visitados por formigas. Entretanto, T. formosa tem um único nectário que desempenha funções multivalentes, podendo ser tanto nupcial, quanto extranupcial. Adicionalmente, a espécie também atrai formigas aos botões no início da fase de desenvolvimento cujas corolas são abortadas. Neste contexto, para melhor compreender a interação entre T. formosa e formigas, este trabalho teve como objetivos: a) caracterizar as estruturas das distintas fases do nectário da espécie e a composição química de seus açúcares; b) determinar se existe mudança estrutural e/ou química que seja correspondente com o papel ecológico de cada estágio; c) analisar a dinâmica de secreção do néctar em cada um dos estágios de atividade do nectário; e d) quantificar o investimento da planta no recurso para a atração de formigas e o efeito destas no êxito reprodutivo. Nossos resultados indicam que o nectário apresenta características de tecido secretor ativo durante todos os estágios, assim como a presença de cristais de oxalato de cálcio no tecido secretor e em outras partes do fruto que contribuem com a proteção contra herbívoros. Nós observamos que formigas diminuem significativamente o dano foliar causado por herbívoros, porém não tiveram efeito sobre a produção de sementes. Deste modo, Tocoyena formosa direcionaria os recursos obtidos na fotossíntese para a secreção do néctar através de uma única estrutura secretora, e assim protege as folhas e, indiretamente, os frutos e sementes em desenvolvimento. Destacamos que este trabalho descreve pela primeira vez a ocorrência de atividade de secreção de néctar em botões florais que perdem a corola de forma prematura, e aqui o denominamos de nectário pré-floral.
Plants offer food resources to many animal species through different structures. Among such structures are the nectaries, which are multicellular glands specialized in nectar production and secretion. Nectaries can occur in both reproductive and vegetative parts, and depending on the location can be regarded as floral or extra-floral. However, they can also be classified according to their function in relation to pollination, being nuptial (when their function is related to pollination) or extranupcial (when their function is related to the defense). Tocoyena formosa (Rubiaceae) is a common species of the Cerrado vegetation, whose extrafloral nectaries are visited by ants. However, T. formosa has a single nectary that performs multivalent functions, which can be both nuptial and extranuptial. In addition, the species also attracts ants to the flower buds at the beginning of the development, whose corollas are prematurely aborted. In this context, to better understand the interaction between T. formosa and ants, the main goals of this study were: a) to characterize the nectary structure as well as the sugar chemical composition during the distinct stages of the organ; b) assess whether nectary structure and nectar sugar composition present changes which correspond to the ecological function of each stage of the nectary; c) analyze nectar secretion dynamics of each phase of the nectary; and d) quantify plant investment in the attraction of ants and the effectivity of ants in plant fitness. Our results indicate that the nectary presents characteristics of active secretory tissue during all stages, as well as the presence of calcium oxalate crystals in both secretory tissue and in other parts of the fruit, which may contribute to the fruit protection against herbivores. We observed that ants significantly reduced leaf damage caused by herbivores, but they had no effect on seed production. Hence, Tocoyena formosa direct the resources obtained in the photosynthesis towards the secretion of the nectar through a single secretory structure, and thus protect leaves against herbivores which indirectly may also benefit fruit and seed production. We highlight that our study describes for the first time the occurrence of nectar secretion activity in floral buds that lose the corolla prematurely, that we named here as pre-floral nectary.
Plants offer food resources to many animal species through different structures. Among such structures are the nectaries, which are multicellular glands specialized in nectar production and secretion. Nectaries can occur in both reproductive and vegetative parts, and depending on the location can be regarded as floral or extra-floral. However, they can also be classified according to their function in relation to pollination, being nuptial (when their function is related to pollination) or extranupcial (when their function is related to the defense). Tocoyena formosa (Rubiaceae) is a common species of the Cerrado vegetation, whose extrafloral nectaries are visited by ants. However, T. formosa has a single nectary that performs multivalent functions, which can be both nuptial and extranuptial. In addition, the species also attracts ants to the flower buds at the beginning of the development, whose corollas are prematurely aborted. In this context, to better understand the interaction between T. formosa and ants, the main goals of this study were: a) to characterize the nectary structure as well as the sugar chemical composition during the distinct stages of the organ; b) assess whether nectary structure and nectar sugar composition present changes which correspond to the ecological function of each stage of the nectary; c) analyze nectar secretion dynamics of each phase of the nectary; and d) quantify plant investment in the attraction of ants and the effectivity of ants in plant fitness. Our results indicate that the nectary presents characteristics of active secretory tissue during all stages, as well as the presence of calcium oxalate crystals in both secretory tissue and in other parts of the fruit, which may contribute to the fruit protection against herbivores. We observed that ants significantly reduced leaf damage caused by herbivores, but they had no effect on seed production. Hence, Tocoyena formosa direct the resources obtained in the photosynthesis towards the secretion of the nectar through a single secretory structure, and thus protect leaves against herbivores which indirectly may also benefit fruit and seed production. We highlight that our study describes for the first time the occurrence of nectar secretion activity in floral buds that lose the corolla prematurely, that we named here as pre-floral nectary.
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Palavras-chave
Anatomia, Formigas, Herbivoria foliar, Mutualismo defensivo, Nectário extranupcial, Anatomy, Ants, Defensive mutualism, Extranuptial nectary, Foliar herbivory