Is Cycas revoluta (Cycadaceae) wind‐ or insect‐pollinated?

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.

A quantitative comparison of dispersed spore/pollen and plant megafossil assemblages from a Middle Jurassic plant bed from Yorkshire, UK

“…Pollen production varies greatly among modern cycads, depending on whether wind or insect pollination is dominant (Norstog 1987). Kono and Tobe (2007) demonstrated that the pollen of the modern cycad, Cycas revoluta occurs only in abundance within very close proximity (~2 m) to the cones from which it is released. If Jurassic cycads share such a characteristic, cycad pollen would almost certainly be underrepresented in the sporomorph assemblage.…”

“…The reproductive methods of these plants differ considerably from the exclusively wind dispersed conifers and ferns. Some modern cycads rely on a combination of wind and insect pollination (Niklas and Norstog 1984;Clark and Clark 1987;Tang 1987;Norstog and Fawcett 1989;Ornduff 1990;Pellmyr et al 1991;Wilson 2002;Kono and Tobe 2007;Terry et al 2007), and both fossil cycads and Bennettitales display early evidence of possible insect pollination (Crepet et al 1991;Klavins et al 2005;Labandeira et al 2007). Pollen production varies greatly among modern cycads, depending on whether wind or insect pollination is dominant (Norstog 1987).…”

The Pollination of Mid Mesozoic Seed Plants and the Early History of Long-proboscid Insects1,2,3

“…More convincing documentation of palynophagy on a male cone comes from the Middle Triassic of Antarctica (Klavins et al, 2005), and reproductive features for the similarly aged ^Anarcticycas, a member of the Cycadaceae, that indicate insect pollination (Hermsen et al, 2009). Insects are involved in the pollination of the most plesiomorphic, extant cycad taxon, Cycas L. of the Cycadaceae (Ornduff, 1991;Yang et al, 1999;Kono & Tobe, 2007). Extant Zamiaceae and Stangeriaceae, whose earliest occurrences are Jurassic, are obligately insect pollinated by a spectrum of beetle pollinators, such as Boganiidae, Erotylidae, Belidae, and Curculionidae (Norstog, 1987;Norstog & Fawcett, 1989;Crowson, 1991;Donaldson, 1992;Forster et al, 1994;Norstog et al, 1995;Tang, 1997;Wilson, 2002;Hall et al, 2004;Oberprieler, 2004), and also by the aeolothripid thrips Cycadothrips (Okajima, 2000;Mound & Terry, 2001;Terry et al, 2005).…”

Molecular and Morphological Phylogenetic Analyses of New World Cycad Beetles: What They Reveal about Cycad Evolution in the New World

“…[6][7][8]. Similar experiments and observations on other continents indicate the same for other genera of cycads [9][10][11][12][13][14][15][16][17][18][19]. In a recent seminal work on guidelines for cycad classification, insect symbionts of cycads were identified as having a potentially important impact on cycad classification: "Insects appear to be the primary vectors for pollination [ .…”