The Mutualisms between Korthalsia Trees and their Ant Mutualists

Abstract

Ant-plant mutualisms evolved multiple times around the world, most notably in the Neotropics, Africa, and Southeast Asia. In these mutualisms, the plant provides shelter to the ant and in return, the ant protects the plant from herbivory. The ant-plant mutualism involving the Southeast Asian rattan Korthalsia is not well-understood, and my research serves as a preliminary study of this system. My field study was conducted at the Kuala Belalong Field Studies Center in Brunei, and it focused on understanding the relationship between Korthalsia furtadoana, K. rostrata, K. echinometra, and their various ant mutualists, likely of the Camponotus genus. To investigate the degree to which these ants protect Korthalsia, I measured leaf herbivory and ant aggressiveness and took samples of leaves for nitrogen and phosphorus content analysis. I recorded the heights on the tree of these data points and samples as well. Then, 6 Korthalsia specimens were cut and examined for ant and leaf counts. My results confirmed that the presence of ant mutualists does confer a significant decrease in herbivory in Korthalsia, though this benefit is pronounced at the upper sections of the tree, where the colony was concentrated. Within the ant colony, the larvae occupy the uppermost domatia while the lower domatia are primarily occupied by sterile workers. The reason for this distribution in ant castes is unconfirmed, but I hypothesize that is because of increased domatia rigidity, which offers safety higher in the tree. The foliar N:P molar ratio of Korthalsia is over 6 times higher than the average for a tropical forest, though the species sample size is too small to make broad conclusions about the nutrient balance of the Bornean tropical forest. This study lays the groundwork for areas of further research into the characteristics unique to the Korthalsia-ant mutualism.