Corresponding author: Adriana Sanchez (
Academic editor: Jack Neff
Herbivory significantly impacts the growth and reproduction of plants. Many plants have developed ways to defend against herbivores and one common strategy is to associate with ants. In many ant-plant interactions, ants are known to protect their host. However, in the Neotropical ant-plant genus
Sanchez A, Bellota E (2015) Protection against herbivory in the mutualism between
Herbivory can have significant negative effects on plant fitness. Both the incidence and the impact of damage can vary with leaf ontogeny and the specific tissue being attacked, and herbivory can result in decreased survivorship and reproductive output (
Myrmecophytes (i.e., plants sheltering the colonies of a limited number of ‘plant-ant’ species in hollow structures called domatia and sometimes also providing them with food in the form of extrafloral nectar and food bodies) are pervasive and very diverse in the Tropics (
Several studies have shown that herbivory increases when ants are excluded from their host (e.g.,
Myrmecophytic-plant genera that have received much attention in the literature include
Questions regarding the effectiveness with which ants associated with
This study was carried out at Los Amigos Biological Station ( Amazon Conservation Association Asociación para la Conservación de la Cuenca Amazónica
The species chosen for this study were
Prior to conducting the ant-exclusion experiments we explored two methods of exclusion, in order to determine which was the most effective. Following previous ant-exclusion experiments (e.g.,
To quantify the effects of ants on herbivory, two fully expanded leaves per sapling were monitored, always choosing the third leaf from the apical meristem from two adjacent branches. Prior to ant exclusion, photographs of every leaf were taken using a digital camera. A transparent sheet subdivided in grids of 1 square cm, each with 25 equidistant points within, was placed on top of the leaf, and photographs were always taken from the same distance. Percentage of herbivory was calculated by counting all the points that fell on areas where there was herbivory and divided by the total number of points that covered the leaf area. Photographs of each leaf were taken every two weeks for a total of six weeks.
We conducted a non-parametric Mann-Whitney
Prior to taking the photographs, we conducted observations on the ants’ behavior, recording their patrolling activities and their interactions with potential herbivores and with other ants that occasionally visit
Removal of ant colonies resulted in an increase in the percentage of herbivory. In each time interval (after 2, 4, and 6 weeks) there was a significant increase in herbivory compared to the control (
Seven out of eleven control plants had zero percent herbivory during the six weeks of the experiment. The four other control plants suffered some herbivory by weeks 4 and 6 (~ 1%). In contrast, of the ant-excluded plants, six plants had more than 3% herbivory, having as high as 16% leaf damage (outlier not shown; Fig.
Percentage of herbivory with time for the control and ant-excluded plants (grey). Removing the ant colonies resulted in a significant increase in the percentage of herbivory after 2, 4, and 6 weeks (
From our observations, the most common herbivores were grasshoppers (unidentified;
Interaction between ant workers of
This is the first study to report that
According to the optimal defense theory (
It has also been suggested that the protective role of ants extends to protecting the host against pathogenic fungi (
Ants constitute a rapid and direct line of defense, which can mobilize where they are required (
The effects of herbivory may also extend beyond growth, ultimately affecting reproductive success and fitness of the host. Decreased energy spent on reparative growth could translate into increased energy allocation towards reproduction (
Ant-exclusion experiments revealed that the myrmecophyte
Funding for this study was provided by a grant from the Amazon Conservation Association. We are thankful to all the staff and people at Los Amigos, especially Nigel Pitman. We would also like to thank Megan Frederickson for her valuable comments and guidance through the experiment, and Antonio Coral and Brian Phillips for assistance in the field. Philip Ward kindly helped with identification of the ants, Lee Dyer and David Wagner with caterpillar identification. We would like to thank Doyle McKey and Alain Dejean for their helpful comments during the review process. INRENA-Ministerio de Agricultura in Peru provided the permits necessary for carrying out the experiments in Madre de Dios.