Non‐ant antiherbivore defenses before plant‐ant colonization in Macaranga myrmecophytes

Abstract We examined changes in the intensity of non‐ant defenses of three myrmecophytic Macaranga species before and after the initiation of symbiosis with ants in a Bornean dipterocarp forest. The intensities of non‐ant defenses at different growth stages of each Macaranga species were estimated by measuring the survival rate of larvae of the common cutworm, Spodoptera litura, when the larvae were fed on fresh leaves from seedlings (saplings) at three growth stages of each Macaranga species. In all species, the intensity of the non‐ant defenses when seedlings had not yet received symbiont foundress queens was significantly higher than that after ant defense was well established. These results support the hypothesis that myrmecophytic Macaranga may defend themselves sufficiently via non‐ant defenses before beginning symbiosis with ants and that the intensity of non‐ant defenses may decrease as the symbiont colony size increases. We suggest that, where the status of myrmecophytism changes as plant–ant colonies grow, the decrease in the intensity of non‐ant defenses which we detected after the establishment of ant colonies might generate an optimal allocation of metabolic cost to ant and non‐ant defenses under resource limitations. We also measured leaf toughness, which is considered to be one of the most important agents of non‐ant defenses against herbivorous insects, at different plant stages to assess its contribution to the change in the intensity of non‐ant defenses after ant colonization. However, we found no evidence that changes in leaf toughness have a significant effect on the change in balance of the two antiherbivory mechanisms.