Article ID: MS23-07
The genus Macaranga (Euphorbiaceae) includes myrmecophytes that allow symbiotic ants to nest inside their hollow stems. The plant exhibits a mutualistic relationship with the ants by providing them with so-called “food bodies.” Such symbiotic ants, called “plant-ants,” patrol the surface of the host plants to repel herbivorous insects from the host plants. The ratio of the food body produced by the host plant for the plant-ants to the host plant’s above-ground biomass decreased as the plant grew in Macaranga bancana, a myrmecophytic species. This phenomenon led us to predict that the average number of plant-ants per leaf would decrease as the host plant grew. To test this hypothesis, we counted plant-ant workers on the leaf surface of M. bancana at various stages of its growth in a lowland rainforest in Borneo. We examined the relationship between the number of plant-ant workers per leaf and host plant size. The number of ants per leaf decreased significantly with increasing host plant size. Additionally, the number of plant-ant workers attending to a leaf was significantly higher on younger leaves than on older leaves. However, these differences became significantly smaller as the plants grew. These observations suggest that the need for anti-herbivore defense by plant-ants decreases with increasing tree size and leaf age.
