Match of fruit-scented cone volatile composition with genetic boundary in Cycas revoluta and implications for fruit mimicry pollination

Volatile organic compounds (VOCs) play a vital role in plant communication and influence plant evolution and ecological interactions. Hence, population-level volatile chemical diversity across the landscape influences plant interactions with local biological communities. Cycads have an insect pollination system. VOC studies have largely focused on the Zamiaceae, but there is a need for research on Cycadaceae, especially because of their strong ecological connections with insect pollinators. The widespread and abundant Cycas revoluta Thunb. was chosen to study geographic variation in cone scent, as it has a known beetle pollinator and a previously identified genetic boundary separating two spatial genetic groups across the central Ryukyu Archipelago, Japan. Headspace sampling with solid-phase microextraction (SPME) fibres combined with gas chromatography-mass spectrometry (GC-MS) were used to collect and analyse cone VOCs of C. revoluta. Six sites including both sexes on three Ryukyu islands traversing the genetic boundary were sampled. Between-sex and genetic boundary differences were statistically tested. The VOC profiles were significantly different across the genetic boundary. The fruit-scented cones matched visits of frugivorous pollinators that primarily feed on fermented fruit. We propose fruit mimicry, with sympatric Pandanus odorifer as a candidate mimetic model based on the overlap of reproductive season and the presence of similar dominant VOCs. The study confirmed ethyl acetate as the main VOC in C. revoluta cones rather than the more unusual estragole. Distinct pollination mechanisms were found between the more generalized Cycadaceae and more specialized Zamiaceae which pave the way for further study of ecological interactions with antagonist and mutualist forces, such as differences in herbivore and pollinator compositions across the genetic boundary.