Pollination drops, pollen, and insect pollination of Mesozoic gymnosperms

Abstract

Recent focus on plant-insect associations during the angiosperm radiation from the last 30 million years of the Early Cretaceous has inadvertently de-emphasized a similar but earlier diversification that occurred among gymnosperms. The existence of gymnosperm-insect associations during the preangiospermous Mesozoic is evidenced by mouthparts capable of reaching and imbibing pollination drops or similar fluids, availability of pollen types consistent with entomophily, and opportunities for related consumption of pollen, seeds, and reproductively associated tissues in major seed-plant groups, namely seed ferns, conifers, cycads, bennettitaleans, and gnetaleans. Based on stereotypical plant damage, head-adherent pollen, gut contents, wing structure, mouthpart morphology and insect damage to plant reproductive organs, the likely nectarivores, pollinivores and pollinators were orthopterans, phasmatodeans, webspinners, sawflies and wasps, moths, beetles, mecopteroids, and true flies. These associations are ranked from possible to probable although the last three insect clades provide the strongest evidence for pollinator activity. We document two mid Cretaceous examples of these associations?cycadeoideaceous bennettitaleans and beetles and a cheirolepidiaceous conifer and flies?for which there are multiple lines of evidence for insect consumption of plant reproductive tissues but also pollination mutualisms. These data highlight the independent origin of a major phase of plant-insect pollinator-related associations during the mid Mesozoic that served as a prelude for the separate, iterative and later colonization of angiosperms.