Induction and relaxation of extrafloral nectaries in response to simulated herbivory in young Mallotus japonicus plants
The disadvantage of induced defenses compared with constitutive defenses is the time during which a plant is vulnerable to herbivory before activation. There is obvious importance in determining the costs and benefits of induced defenses. Some plants produce extrafloral nectaries (EFNs), which attract ants that protect against herbivores, and induce EFNs and extrafloral nectar in response to leaf damage. To understand induction of indirect defense by ants, we investigated the induction and relaxation of extrafloral nectar secretion and EFN formation after artificial leaf damage in young Mallotus japonicus. Plants were grown under control or leaf damage conditions a greenhouse or in the field. Following artificial leaf damage, we assessed secretion of extrafloral nectar and the number of ant workers on plants. We measured the number of EFNs on each of seven leaves produced after leaf damage. Extrafloral nectar secretion was induced within 1 day following leaf damage, resulting in the attraction of numerous ant workers, and the extrafloral nectar secretion decreased to initial levels after 7 days. The number of EFNs was largest on the first leaf and smallest on the sixth leaf produced after leaf damage, but the total number of EFNs did not differ between treatments. Thus, M. japonicus rapidly induces extrafloral nectar secretion after leaf damage, followed by relaxation. Furthermore, following induction of EFNs on newly produced leaves, it may decrease the cost of induction by reducing the number of EFNs on leaves produced later.
KeywordsAnt Induced defense Indirect defense Leaf damage Herbivory
We thank T. Yokota and S. Suematu for their assistance in the experiments. Thanks are also extended to R. Kishida for his advice on statistics. We express our gratitude to M. Kinoshita, N. Katayama, and K. Tanaka for their encouragement and advice provided throughout the study. This work was supported in part by a Research Fellowship from the Japan Society for the Promotion of Science (JSPS) for Young Scientists (234305) and a JSPS Grant-in-Aid for Young Scientists (B) (No. 15K18611).
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