Graduate School of Human and Environmental Studies, Kyoto University, Yoshida-Nihonmatsu, Sakyo-ku, Kyoto 606-8501, Japan.
J Plant Res. 2013 Jan;126(1):73-9. doi: 10.1007/s10265-012-0500-z. Epub 2012 Jun 1.
Macaranga myrmecophytes (ant-plants) provide their partner symbiotic ants (plant-ants) with food bodies as their main food, and they are protected by the plant-ants from herbivores. The amount of resource allocated to food bodies determines the plant-ant colony size and consequently determines the intensity of ant defense (anti-herbivore defense by plant-ants). As constraints in resource allocation change as plants grow, the plant-ant colony size is hypothesized to change with the ontogenesis of Macaranga myrmecophyte. To determine the ontogenetic change in the relative size of the plant-ant colony, we measured the dry weights of the whole plant-ant colony and all of the aboveground parts of trees at various ontogenetic stages for a myrmecophytic species (Macaranga beccariana) in a Bornean lowland tropical rain forest. Ant biomass increased as plant biomass increased. However, the rate of increase gradually declined, and the ant biomass appeared to reach a ceiling once trees began to branch. The ant/plant biomass ratio consistently decreased as plant biomass increased, with the rate of decrease gradually accelerating. We infer that the ontogenetic reduction in ant/plant biomass ratio is caused by an ontogenetic change in resource allocation to food rewards for ants related to the physiological changes accompanying the beginning of branching.
大油桐（蚁栖树）为其共生蚂蚁（蚁栖植物）提供食物体作为主要食物，并受到蚁栖植物的保护，免受食草动物的侵害。分配给食物体的资源量决定了蚁栖植物的蚁群大小，从而决定了蚁栖植物的防御强度（蚁栖植物对食草动物的防御）。由于资源分配的限制随着植物的生长而变化，因此假设蚁栖植物的蚁群大小会随着大油桐的个体发育而变化。为了确定蚁栖植物蚁群相对大小的个体发育变化，我们在婆罗洲低地热带雨林中，对一种蚁栖植物（Macaranga beccariana）的各个个体发育阶段，测量了整株蚁栖植物蚁群和所有地上部分的干重。蚁群生物量随着植物生物量的增加而增加。然而，增加的速度逐渐下降，一旦树木开始分枝，蚁群生物量似乎就达到了一个上限。随着植物生物量的增加，蚁/植物生物量的比值持续下降，下降速度逐渐加快。我们推断，蚁/植物生物量比值的个体发育减少是由于与分枝开始伴随的生理变化相关的资源分配给蚁类食物奖励的个体发育变化引起的。
