THE HISTORY OF HERBIVORY ON SPHENOPHYTES: A NEW CALAMITALEAN WITH AN INSECT GALL FROM THE UPPER PENNSYLVANIAN OF PORTUGAL AND A REVIEW OF ARTHROPOD HERBIVORY ON AN ANCIENT LINEAGE

摘要

Premise of research. Sphenophytes are a modestly diverse lineage of vascular plants with a persistent record extending from the late Paleozoic to the present. However, patterns of arthropod herbivory on sphenophytes are poorly known because of a scattered literature, which we address in this report. Methodology. We document the 315-million-year-long record of sphenophyte-arthropod herbivory by focusing on the bookends of that record-namely, the Pennsylvanian and the present day. We add to this milieu a gall association on a newly described sphenophyte from the Upper Pennsylvanian of Portugal. Pivotal results. Earliest-known sphenophyte herbivory is Early Pennsylvanian, when virtually all interactions involved piercing-and-sucking damage by stylate insect mouthparts and lesions from cutting-and-slicing ovipositors. An exception is a newly discovered calamitalean (Annularia paisii sp. nov.) that harbored a newly discovered insect-induced gall (Paleogallus carpannularites ichnosp. nov.) that is similar to a modern fern gall. This discovery suggests that Late Pennsylvanian interactions were more diverse than previously suspected. By the end of the Pennsylvanian, the component community of one whole-plant calamitalean species had 12 damage types (DTs), only one of which was nonpuncturing damage. Shifts to external foliage feeding, mining, and galling are evident during the Late Triassic. A Middle Jurassic renewal of interactions was followed by a decrease in documented DTs present in the Cretaceous and Cenozoic. Fifteen modern species of the genus Equisetum, the sole surviving sphenophyte lineage, exhibit four herbivory patterns. First, almost all documented herbivory is confined to the seven species of Equisetum (horsetails), not subgenus Hippochaete (scouring rushes). Second, there are diversification events of four genera of herbivores-a beetle, two sawflies, and a fly-on subgenus Equisetum. Third, this arthropod herbivory is approximately evenly split among monophagy, oligophagy, and polyphagy. Fourth, the herbivore component community of Equisetum arvense L. (field horsetail) is diverse, representing 10 major feeding modes, comparable to a modern angiosperm species; there are considerably more feeding modes for E. arvense than there are for Pennsylvanian calamitaleans. Conclusions. Pennsylvanian sphenophytes supported few folivores, and there was a major shift in the modes of sphenophyte herbivory after the Paleozoic. Considerable modern herbivory is localized on E. arvense.