Conspicuous extra‐floral nectaries are inducible in Vicia faba

Abstract

Mutualistic interactions are dynamic associations that vary depending on the costs and benefits to each of the interacting parties. Phenotypic plasticity in mutualistic interactions allows organisms to produce rewards to attract mutualists when the benefits of their presence outweigh the costs of producing the rewards. In ant–plant defensive mutualisms, defences are indirect as plants produce extra‐floral nectaries (EFN) to attract predatory ants to deter herbivores. Here we demonstrate that in broad bean, Vicia faba, the overall number of EFNs on a plant increases dramatically following leaf damage. In two damage treatments, removal of: (1) one‐third of one leaf in a single leaf pair or (2) one‐third of both halves of a single leaf pair, resulted in a 59 and 106% increase in the number of EFNs on the plants, respectively, over 1 week. We suggest that the increased production of visually conspicuous EFNs is an adaptive inducible response, to attract predatory arthropods when risk of herbivory increases.

<i>Rhizobium</i> alters inducible defenses in broad bean, <i>Vicia faba</i>

“…Increased nectar production may also be inducible depending upon environmental conditions [13,16]. In broad bean, EFNs are located on the stipules at the base of each leaf petiole [17,18]. Attractive to ants [18,19], broad bean plants increase EFN numbers when herbivory increases [17,20].…”

“…Attractive to ants [18,19], broad bean plants increase EFN numbers when herbivory increases [17,20]. As broad bean EFNs are visually conspicuous it may be adaptive to produce a more striking visual display rather than to augment nectar from existing nectaries [17].…”

The Ecology of Extrafloral Nectar in Senna mexicana var. chapmanii

“…Inducible EFN nectar production has been reported in many species (Stephenson 1982;Koptur 1989;Agrawal & Rutter, 1998;Mondor & Addicott 2003;Lach et al 2009;. Indeed, increased EFN production in response to leaf damage has been observed previously in S.…”

“…Numerous studies have reported increased EFN production in response to leaf damage (Stephenson, 1982;Koptur, 1989;Agrawal and Rutter, 1998;Mondor and Addicott, 2003;Lach et al, 2009). In most cases, however; only the volume or concentration of nectar is reported, and the period of elevation is no greater than 48…”

“…It is not surprising, therefore, that plants adjust nectar production over time, and in response to herbivory . Several studies addressing EFN secretion have demonstrated increased production in response to mechanical leaf damage (e.g., Stephenson, 1982;Koptur, 1989;) and herbivory (Koptur, 1989;Agrawal and Rutter, 1998;Mondor and Addicott, 2003). Both the volume of nectar produced by each nectary , and the number of nectaries (Mondor and Addicott, 2003) have been seen to increase in damaged or herbivore infested plants.…”