THREE INFORMATIVE INSECT-GYMNOSPERM INTERACTIONS FROM THE MID-MESOZOIC: LATE TRIASSIC SEED PREDATION, MIDDLE JURASSIC MIMICRY, AND EARLY CRETACEOUS POLLINATIION

The phenomenology and theory of plant-insect interactions overwhelmingly have been derived from angiosperms occurring under the environmental conditions of the modern world. However, the Mesozoic fossil record offers a considerably different perspective than that of modern studies, suggesting that much of the novelty claimed for modern angiosperm-insect interactions has an earlier existence in a world dominated by gymnosperms that lived in a significantly different physical environment from that of today. We present from our collective research three examples of interactions that provide glimpses of the antagonistic and mutualistic roles that three insect lineages had on their host plants. The first is seed predation, an interaction in which the female plant gametophyte is killed by consumption of embryonic and associated nutritive tissues from a variety of herbivorous insects. Several lake deposits of the Late Triassic Molteno Formation (ca. 230 Ma) of South Africa provide evidence for targeted and occasionally elevated levels of seed predation on a broad spectrum of ginkgophyte (Avatia), corystosperm (Fanerotheca), conifer (Dordrechtites) and other seeds by the piercing-and-sucking activities of the Heteroptera (true bugs). During the latest Middle Jurassic (165 Ma) at Daohugou, a lake site in Inner Mongolia, northeastern China, there developed an association between the ginkgoalean leaf, Yimaia capituliformis (the model), and the hangingfly Juracimbrophlebia ginkgofolia (the mimic), a member of the Mecoptera. In this case of mimicry, the shape, size, outline, surface texture and other features of the leaf were reproduced almostly exactly by the insect. Last, in the late Early Cretaceous (110 Ma) of northern Spain, miniscule thrips fossils of Gymnopollisthrips (Order Thysanoptera) bore specialized structures (ring setae) nvolved in pollination of either the ginkgophyte Nehvizdyella (more likely) or an unnamed cycad (less likely). The plant host of this mutualism remains uncertain, as Cycadopites pollen found clustered on the pollinator's ring setae could ot be identified to species. These three associations provide evidence that the mid-Mesozoic world of plant-insect relationships may have been as dynamic as those of more recent angiosperms.