Date Published: January 31, 2017
Publisher: Public Library of Science
Author(s): Ernesto Oliveira Canedo-Júnior, Graziele Silva Santiago, Luana Fonseca Zurlo, Carla Rodrigues Ribas, Rafaela Pereira Carvalho, Guilherme Pereira Alves, Mariana Comanucci Silva Carvalho, Brígida Souza, Martin Schädler.
Ant-aphid interactions may affect host plants in several ways, however, most studies measure only the amount of fruit and seed produced, and do not test seed viability. Therefore, the aim of this study was to assess the effects of the presence of ant-aphid interactions upon host plant productivity and seed viability in two different contexts: isolated and within an arthropod community. For this purpose we tested the hypothesis that in both isolated and community contexts, the presence of an ant-aphid interaction will have a positive effect on fruit and seed production, seed biomass and rate of seed germination, and a negative effect on abnormal seedling rates, in comparison to plants without ants. We performed a field mesocosm experiment containing five treatments: Ant-aphid, Aphid, Community, Ant-free community and Control. We counted fruits and seeds produced by each treatment, and conducted experiments for seed biomass and germinability. We found that in the community context the presence of an ant-aphid interaction negatively affected fruit and seed production. We think this may be because aphid attendance by tending-ants promotes aphid damage to the host plant, but without an affect on seed weight and viability. On the other hand, when isolated, the presence of an ant-aphid interaction positively affected fruit and seed production. These positive effects are related to the cleaning services offered to aphids by tending-ants, which prevent the development of saprophytic fungi on the surface of leaves, which would cause a decrease in photosynthetic rates. Our study is important because we evaluated some parameters of plant fitness that have not been addressed very well by other studies involving the effects of ant-aphid interactions mainly on plants with short life cycles. Lastly, our context dependent approach sheds new light on how ecological interactions can vary among different methods of crop management.
Plants are relatively immobile organisms and so they are intimately linked to the physical conditions of their environment and how it varies over the time . However, the biotic community present in a given environment can also deeply affect a plant community. Several organisms, from microscopic  to large herbivores , can affect, both directly and/or indirectly, plant occurrence, evenness and productivity. Such organisms may affect plants indirectly by causing changes to environmental conditions [4, 5], or directly through disease, parasitism, competition and herbivory . Among the many organisms that can affect plants, insects are of particular importance mainly because of their impact on the yield of cultivated plants, and so they are frequently considered major pests in those systems [7,8].
In total we sampled 15 aphid-tending ant morphospecies from nine genera. The most diverse genera were Camponotus and Pheidole, with three aphid-tending ant morphspecies each, and Linepithema and Brachymyrmex, with two aphid-tending ant morphospecies each. The genera Hylomyrma, Dorymyrmex, Gnamptogenys, Ectatomma and Crematogaster had only one ant morphospecies each (S1 Table).
In our study we assessed the effects of the presence of an ant-aphid interaction on host plant fitness. According to our experiments, the presence of the ant-aphid interaction negatively affected the number of fruits and seeds when in a community context, but did not have an effect on seed biomass and viability. On the other hand, in an isolated context (i.e. without arthropod community), the ant-aphid interaction positively affected fruit and seed production.