Assimetria flutuante, herbivoria e polinização em melastomataceae

• Ano de defesa: 2011
• Autor(a) principal: Cristina Costa Telhado Pereira
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Minas Gerais; UFMG
• Palavras-chave em Português: Melastomataceae; Herbivoria; Assimetria Flutuante; Polinização; Ecologia
• Link de acesso: http://hdl.handle.net/1843/BUOS-8MXF64

Fluctuating Asymmetry (FA) represents small, random variations in characters presumably with bilateral symmetry and is a widely used measurement of developmental instability in plants and animals. Because AF is a quick, simple and reliable measure, it has been frequently used for monitoring levels of environmental stress, either abiotic, biotic or both. In plants, fluctuating asymmetry is usually measured by deviations of an axis of symmetry, primarily using the midrib or distances between peripheral veins as reference axes. Besides being an indicator of stress, several studies have shown a positive relationship between asymmetry and abundance of herbivores, indicating that FA can serve as a reliable predictor of susceptibility to herbivory in natural and artificial communities. Recently, fluctuating asymmetry has also been suggested as a surrogate of plant quality for pollinators, and could be measured in features like nectar guides, petal size, stamens and pistils. This study investigated the effects of fluctuating asymmetry in negative interactions such as herbivory, and also on positive interactions, such as mutualistic relationships between plants and pollinators at three levels: species, genera and family. To achieve that aim 20 individuals of five species (1- Trembleya laniflora, 2- T. parviflora, 3- Lavoisiera campos-portoana, 4- L. cordata and 5- Tibouchina heteromalla) of the family Melastomataceae were marked in the field and monitored before and during the flowering season. After the width of their leaves and the width and length of their flowers were measured, the Index 1 of AF was calculated as the mean of the difference of the width/length between the left and right sides. The role of fluctuating asymmetry in herbivory rates and pollinator visitation variation within and among these host plants was studied. All species studied exhibited asymmetry in the leaves and flowers, and only the leaves of L. campos-portoana and L. cordata, and the petals of T. heteromalla did not exhibited fluctuating asymmetry. The highest level of leaf asymmetry was found in T. heteromalla and of length and width of petals in L. campos-portoana. The species T. parviflora and T. heteromalla have leaves with greater degree of asymmetry than 12 flowers (length and width), L. campos-portoana has the flowers (length and width) with the highest level of asymmetry and T. laniflora has the highest degree of asymmetry in the petal width. None of the studied species exhibited a positive relationship between the level of asymmetry of the leaves and flowers at an individual basis. All species showed a higher degree of AF in leaves attacked by herbivores compared to intact leaves, and for the species of the genera Trembleya this difference was significant. Similarly, pollinators also seemed to use AF as guide, preferring the more symmetric flowers of T. laniflora. For the studied species, fluctuating asymmetry may not be used as an indicator of stress exposure because there was no consistency in the comparisons of the degrees of FA of leaves and flowers within a species. Similarly, FA cannot be used as a predictor of development instability once no species exhibited a relationship between an individual degree of leaf and flower fluctuating asymmetry. However, this study showed that herbivores that interact with these species generally use fluctuating asymmetry as a guide for their choice