During a two week field trip (2017) to the Chiquibul Forest Reserve in Belize, small research projects were conducted. My group investigated the neotropical symbiotic relationship between acacia trees and the Pseudomyrmex genus of ants. Proxy caterpillars were made from a modelling clay and distributed on 40 acacias that housed ants and 40 mimosa sp. that did not have a symbiotic relationship. The caterpillars were used to assess the extent of attack occurrence by the ants and therefore, the efficacy of the mutualism.
There was a higher mean attack occurrence on the caterpillars that were placed on the acacia trees, suggesting that the ant-acacia association was highly effective. In addition, we discovered that there was a ‘parasitic’ species of ant, invading the mutualistic relationship. This species offered a lower level of protection to the acacia than its obligate mutualist.
Publication is currently being worked towards.
An untouched model caterpillar (top) and one that had been attacked and disfigured by ants (bottom).
©Lara Jackson | @lara_wildlife
Utilising ant species as a form of defence is employed by one third of the world’s plants; these interactions are particularly abundant in tropical ecosystems and the degree of association can vary from a loose connection to an obligate mutualism. In the Neotropics, the mutualism between Acacia spp. and the Pseudomyrmex genus of ant is well documented. The Chiquibul Forest Reserve of Belize is dominated by Acacia gentlei which is known to be associated with Pseudomyrmex ferruginea and Pseudomyrmex gracilis.
Model caterpillars were used to assess the extent of attack occurrence; there was a significant difference between the mean attack occurrence on the models placed on A. gentlei and a Mimosa sp. that was morphologically similar but lacked an ant-plant mutualism. This suggested that the Pseudomyrmex-Acacia association was highly effective at defending the plant from other herbivores. Without its ant inhabitants, the acacia would be quickly overcome.
Furthermore, P. ferruginea offered a higher degree of protection to its host than P. gracilis as they achieved a significantly higher mean attack occurrence on the model caterpillars. This corroborates other studies that found that P. ferruginea is an obligate mutualist and relies upon the Acacia for survival. In comparison, P. gracilis appears to be a parasite to the mutualism, reaping the benefits offered by the interaction without paying the costs.
To find out more, please click here.