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Is Cycas revoluta (Cycadaceae) wind- or insect-pollinated?¹

Department of Botany, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan

ABSTRACT

Among the Cycadales (Cycadaceae and Zamiaceae), the Zamiaceae are known to be insect-pollinated. In contrast, the Cycadaceae are still considered wind-pollinated, although some doubt has been cast on several species, including Cycas revoluta. Using a large population of C. revoluta on Yonaguni Island (Okinawa, Japan), we performed exclusion experiments, documented insects from male and female cones, and analyzed the morphology of the apical part of the ovule to determine the pollination method of this species. Insect exclusion resulted in a notable reduction in seed set, except in a few individuals growing near male cones. The amount of airborne pollen was abundant within a 2-m radius of male cones but decreased markedly beyond this distance. Pollen grains of C. revoluta were found on the body of Carpophilus chalybeus (Nitidulidae, Coleoptera), one of a few species of insects collected from both male cones and female cones far from males. We conclude that C. revoluta relies on both wind (anemophily) and insect pollination (entomophily), although such anemophily is restricted to female trees growing within a 2-m radius of male trees. The nitidulids are not host specific to this cycad and primarily feed on plant tissue but serve as pollinators during pollen release. Cycas revoluta appears to be in an initial mode of animal pollination, as opposed to the host-specific insect pollination observed in most Zamiaceae.

Key Words: ambophily • anemophily • Cycadaceae • Cycas revoluta • entomophily • Nitidulidae • pollination