Extrafloral nectar as entrée and elaiosomes as main course for ant
visitors to a fireprone, mediterranean-climate shrub
Abstract
Thousands of plant species produce both extrafloral nectaries (EFNs) on
their leaves and nutrient-rich appendages on their diaspores
(elaiosomes). Although their individual ecology is well-known, any
possible functional link between them has been ignored. Here, we
recognized their co-presence in the shrub, Adenanthos cygnorum
(Proteaceae), and studied their function and interaction. We observed
that ants frequently visit both structures, seeds are attractive to
vertebrate granivores but are released into a leafy cup from where they
are harvested by ants and taken to their nests, from which seeds,
lacking elaiosomes, germinate after fire. We showed that juvenile plants
do not produce EFNs and are not visited by ants. We conclude that EFNs
are not just an indirect adaptation to minimize herbivory via aggressive
ants (or parasitoid wasps) but specifically enhance reproductive success
by inducing ants to visit the plant throughout the year, promoting
discovery of the seasonally available, elaiosome-bearing seeds on the
plant and transporting them to their nests, so avoiding the risk of
granivory should seeds fall to the ground.