Extrafloral nectary-bearing plant Mallotus japonicus uses different types of extrafloral nectaries to establish effective defense by ants

Akira Yamawo,Jun Tagawa,Nobuhiko Suzuki

doi:10.1007/s10265-019-01119-5

Akira Yamawo, Jun Tagawa + Show 1 more

Open Access

https://doi.org/10.1007/s10265-019-01119-5

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Abstract

Extrafloral nectary (EFN)-bearing plants attract ants to gain protection against herbivores. Some EFN-bearing plants possess different types of EFNs, which might have different effects on ants on the plants. Mallotus japonicus (Thunb.) Muell. Arg. (Euphorbiaceae) bears two types of EFNs, including a pair of large EFNs at the leaf base and many small EFNs along the leaf edge. This study aimed to determine the different roles of the two types of EFNs in biotic defense by ants. A field experiment was conducted to investigate the effect of leaf damage on EFN production and on the distribution pattern of ants. After leaf damage, the number of leaf edge EFNs increased in the leaves first-produced. The number of ants on the leaves also increased, and the foraging area of ants extended from the leaf base to the leaf tip. An EFN-covering field experiment revealed that leaf edge EFNs had a greater effect than leaf base EFNs on ant dispersal on leaves. The extended foraging area of ants resulted in an increase of encounter or attack rate against an experimentally placed herbivore, Spodoptera litura. These results suggest that M. japonicus plants control the foraging area of ants on their leaves using different types of EFNs in response to leaf damage, thus achieving a very effective biotic defense against herbivores by ants.

Highlights

Mutualism is an interaction between different species that enhances the fitness of both partners involved
Regarding the functions of extrafloral nectary (EFN), the results demonstrate that the two types of EFNs in M. japonicus exhibit somewhat different effects on the plant’s ant partners
The leaf base EFNs play the fundamental role of ant attraction, whereas the role of the leaf edge EFNs is to extend the foraging area of ants from around the leaf base to the leaf tip, in addition to attracting ants

Summary

Introduction

Mutualism is an interaction between different species that enhances the fitness of both partners involved. In a type of plant–animal mutualism involving the exchange of resources for services, plants provide nectar [floral and extrafloral (EF) nectar] as a food resource to pollinator partners (Armbruster 1993) and to predatory ant partners capable of deterring the plant’s natural enemies, such as herbivorous insects (Bronstein 1998; Koptur 1992). In such a type of mutualistic system, plants have evolved mechanisms to control the behavior of their partners to increase their own benefits (reviewed in Grasso et al 2015). Ant partners depend on Acacia trees that secrete sucrose-free EF-nectar (Heil et al 2014)

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