Ant-Plant Mutualisms

By Claire Jackan      

          For our final project of the semester, my partner and I investigated the extent of the relationship between ants and the plant Pentaclethra macroloba in varying degrees of light intensity. Here at La Selva, we participated in independent, as opposed to faculty-led, projects. This means that my partner and I came up with the idea for our experiment and designed the methods ourselves.  We were curious to learn more about how environmental factors may affect ant-plant associations.  Some ant-plant relationships are strict mutualisms; in other words, the plant produces nutritious food bodies to attract a specific species of ant, which in turn protects the plant from herbivory by attacking insects and removing larvae from the leaves.  However, the relationship between ants and P. macroloba is known as a diffuse mutualism because while both the plant and the ants benefit from the interaction, it is an indirect benefit and not required for their survival.  The plant still produces food (within extrafloral nectaries) to attract the ants, but it is a smaller reward in terms of nutritious value. The ants that come are typically generalists (not necessarily a specific species) and they still provide some protection against herbivory by patrolling the leaves and occasionally removing a potential herbivore.

            We thought that plants with access to more sunlight would have more resources and energy available to allocate towards producing higher quality extrafloral nectaries that would in turn attract more ants. We tested this hypothesis by placing small pieces of tuna on the leaves of P. macroloba plants and measuring how long it took for the ants to appear on the leaf and how long it took for them to actually make contact with the tuna. Other variables we recorded included the height of the plant, the number of extrafloral nectaries, percent herbivory, and canopy cover.  Counting the extrafloral nectaries proved much more difficult than I anticipated, as they are so small that I had to use a magnifying glass and a light in order to be able to see them at all. The weather was also an obstacle at times; we couldn’t set up the tuna baits when it was raining because the ants are not active during rain and it would have just washed off the leaves anyway.

            At the end of the project, we were able to share our results not only with the class but also at a poster session in which we presented in Spanish to the local community.  Though at times it was challenging to communicate exactly what I wanted to say, I’m really grateful to have had the opportunity to practice my Spanish, especially since I had to utilize a more scientific vocabulary than I am accustomed to. I think the combination of the independent project and poster presentation was the perfect way to culminate the semester by bringing together everything I have learned and sharing it both with my peers and with the local community.