THE POLLINATION OF MID MESOZOIC SEED PLANTS AND THE EARLY HISTORY OF LONG-PROBOSCID INSECTS

A defining event for Mesozoic plant-pollinator interactions is the angiosperm radiation, which extended the reach of pollinating insects during the Early Cretaceous in a brief interval of geologic time. Recent evidence indicates that events beginning in the Early Permian and increasing during the Middle Jurassic provided repeated opportunities for insect feeding on pollen, pollination drops, and reproductive tissues of extinct gymnosperm lineages. Pollination was an associated development. Studies on the detailed mouthpart structure of several fluid-feeding insect lineages indicate targeting of certain tubular features of gymnosperm ovulate organs that previously were considered anomalous and difficult to interpret. One mouthpart type, the long-proboscid condition, consists of elongate, tubular (siphonate) proboscises that accessed surface fluids powered by a cibarial pump, often assisted with a distal proboscis sponging organ. These proboscises were received in ovulate organs through often intricate cupulate integumental tubes, interovular channels, salpinx tubuli, pappus tubules, prolonged micropyles, and a catchment funnel-pipe-micropyle device. These ovulate structures also are consistent with insect access to nutritive rewards, including pollination drops, nectarial secretions, and pollen. Other evidence for pollination includes the entomophilous structure and size of pollen found on insect and plant contact surfaces and in insect guts, nutritional levels of modern pollination chop fluids similar to angiosperm nectar for supporting metabolically high activity levels of aerially active insects, and plant-host in crossing. While the long-proboscid pollination mode of fluid feeding targeted gymnosperm hosts that deployed unisexual reproductive organs at some distance from each other, either on the same or on different plants, another mode of pollination, that of mandibulate insects, consumed typically solid tissues in compact bisexual strobili, targeting pollen and perhaps pollination drops (adults), and associated sterile tissues (larvae). These two groups of pollinator associations were irretrievably altered as angiosperms diversified during a 35-million-year interval of the Early Cretaceous, evident in three patterns. First was the demise of roost pollinator associations that evolved during the preceding 65 million years; second was the lateral transfer of sonic of these associations onto angiosperms that continue today as relicts; and third was emergence of new pollinator associations with angiosperms.