Fossil Insect Palynivory and Pollination: Role of Plant Damage, Coprolites, and Gut ContentsLabandeira, C.C.
Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560, USA; Entomology, University of Maryland, College Park, MD 20742, USA
The fossil record of vascular plant and insect associations contain five types of data that indicate insect consumption of spores, prepollen, and pollen (palynivory) and also address the origin of pollination mutualisms. These types of evidence are, starting from the plant end and containing to the insect end: (1) entomophilous plant reproductive features, (2) insect damage of plant reproductive tissues, (3) matrix dispersed coprolites, (4) insect gut contents, and (5) insect mouthpart and ovipositor structure. Of these, the middle three represent direct effects by insects of plant tissue consumption and provide a significant fossil record documenting the associations between palynivorous insects and vascular plants from the earliest land ecosystems to the recent. Accordingly, four distinctive assemblages of vascular plant/palynivore associations characterize the terrestrial fossil record.
The first assemblage occurs from latest Silurian to Middle Devonian and represents basal vascular plant hosts whose animal associates are unknown, but probably were insects or possibly other terrestrial arthropods. The second assemblage is documented from the Middle Pennsylvanian to the Late Permian and represents pteridiphytes and basal seed plants associated with palaeodictyopteroid, hemipteroid, and basal neopteran insects. Plants whose miospores were consumed include marattialean ferns, cordaites, and medullosan and glossopterid pteridosperms, and early gnetophytes, and includes damage to pteridosperm prepollen organs. Interacting insect representatives were members of the palaeodictyopterans, hypoperlids, psocopterans, grylloblattodeans, and possibly orthopterans, and probably were attracted to sugary fluid rewards such as pollination drops, nectaries on vegetative tissues, and honeydew. The third assemblage originated during the Middle Triassic to mid-Cretaceous, but has persisted to the present. Interacting plants include bennettitaleans; cycads; voltzialean, pinacean, and cheirolepidaceous conifers; and advanced gnetaleans. Associated palynivorous or seed-predating insects are prophalangopsid grasshoppers, and more basal lineages of holometabolous insects, such as nemestrinid flies, xyelid sawflies, and nemonychid weevils. Fluid sugar rewards were provided by the pollination drop mechanism and extrastrobilar nectaries. The fourth assemblage is found from the Early Cretaceous to the present, and consists of angiosperms whose associates are predominantly thrips and more derived lineages of holometabolous insects, of which the predominant sugar fluid reward is floral nectaries.
Hypotheses regarding the origin of pollination have overwhelmingly focused on the phylogenies of extant plant and insect groups, without consideration of an illuminating and relevant fossil record. Importantly, the fossil record documents four assemblages of plant/palynivore associations, of which the first two are extinct, most of the third is gone, and the fourth overwhelmingly dominates the extant biota. Consideration of plant damage, coprolites, and gut contents in the preangiospermous fossil record can provide a crucial perspective for understanding the formative processes and events characterizing the history of pollinivory and the origin of pollination.
Labandeira, C.C. 2000. The paleobiology of pollination and its precursors. In: R.A. Gastaldo and W.A. DiMichele, (eds.), Phanerozoic Terrestrial Terrestrial Ecosystems. Paleontological Society Papers, 6: 233-269.