Abstract
To reduce herbivory, plants bearing extrafloral nectaries interact with ants and attract them by providing food. As plant bodyguards, ants respond to the resource provision and, using their antennae, detect chemical messages from the host plants that help them to locate herbivores. Ants can also use their vision to explore the environment; however, information is lacking on how interactions between visual signs and the availability of extrafloral nectar affect ant aggressiveness near resources. We addressed the following question in this study: does the ants’ ability to visualize potential herbivores enhance their aggression under a constant provision of a high-quality food source? Using an experimental approach within the semiarid intertropical region of Tehuacan-Cuicatlán (Mexico), we manipulated the availability of food sources by constantly offering artificial nectaries on the shrub Prosopis laevigata (Fabaceae). Over two time periods (day and night), we tested how the presence of a high-quality food source affected ant aggressiveness to herbivores. Therefore, we offered dummy caterpillars and counted the number of marks left by enemy attacks. Overall the attack rate was extremely high: 84.25% of the dummy caterpillars were injured. Ants were responsible for 86.22% of the marks left by enemies, and their aggression increased during the day, especially towards caterpillars in trees with high-quality food sources. During the night, ants probably rely mostly on their antennae to detect potential herbivores; therefore, their ability to detect dummy caterpillars was greater during the day. We show that, besides nectar quality and availability, visualizing herbivores may enhance ant aggressiveness.
Highlights
Herbivory is a biotic interaction between plants and animals that has a variety of consequences for plants, from partial leaf loss to the death of whole organisms (Herrera & Pellmyr, 2002)
Considering that ants can visually detect potential herbivores (Knaden & Graham, 2015; Leles et al, 2017) and the differences in visual accuracy between nocturnal and diurnal species (Yilmaz et al, 2014), how would the constant provision of high-quality food sources over day-night periods affect ant aggressiveness? Would the aggressiveness of ants be enhanced by the interaction between chemical and visual stimuli? The aim of our study was to evaluate the effects of a constant source of food during day-night periods on ant aggressiveness towards potential herbivores in a population of P. laevigata
We found that the interactions between detecting a food source and visual signs enhanced ants’ aggressiveness towards potential invaders
Summary
Herbivory is a biotic interaction between plants and animals that has a variety of consequences for plants, from partial leaf loss to the death of whole organisms (Herrera & Pellmyr, 2002). Plants feed ants in exchange for protection against potential herbivores (Koptur, 1984; Campos & Camacho, 2014; Dáttilo et al, 2017; Lange et al, 2017). This relationship is subject to environmental constraints (e.g. temperature and humidity) and the specific characteristics of ants, plants and their natural enemies (e.g. period of activity of ants and nectar quality) (Gottsberger et al, 1984; Falcão et al, 2014;Anjos et al, 2017;Lange et al, 2017)
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