ECOLOGICAL RESPONSES OF ARTHROPOD AND FUNGAL ASSOCIATIONS OF THE MEDULLOSAN PTERIDOSPERM, MACRONEUROPTERIS SCHEUCHZERI, TO LATE PALEOZOIC CLIMATE CHANGE

Arthropod feeding damage diversity on fossil plants is strongly correlated with temperature in Cenozoic deposits, but the effects of climate on the early ecology of insect herbivory in the late Paleozoic remains unexplored. The Middle Pennsylvanian to early Permian was marked by repeated glacial–interglacial cycles associated with shifts between wetland floras during glacial phases and interglacial seasonally dry floras. In addition, a long-term trend of increasing aridity began in the Middle Pennsylvanian and intensified through the early Permian. We present preliminary results of our study tracking the response of arthropod and fungal communities associated with Macroneuropteris scheuchzeri, a long-ranging and abundant medullosan seed fern. We censused arthropod and fungal damage on over 4000 M. scheuchzeri leaf specimens from 30 localities in the Illinois Basin in Illinois and Indiana, the eastern shelf of the Midland Basin in Texas, and the Central Appalachian Basin in West Virginia, spanning an approximately 18 million year period from the upper Bashkirian to early Asselian. We found an overall increase in arthropod and fungal damage-type diversity associated with M. scheuchzeri over the studied interval, peaking near the end-Gzhelian in Texas. Despite broad climatic changes occurring during the temporal range of M. scheuchzeri, several damage types (DTs) were present at most of the localities, including shallow excisions into the leaf margins caused by arthropods (DT12) and U- and V-shaped fungal blotches (DT75 and DT97) along leaf margins. Occasionally, margin feeding crosscuts the fungal blotches, suggesting that arthropods may have targeted leaf tissue previously damaged by fungal pathogens. The repeated co-occurrences of the same DTs throughout the 18 million-year range of M. scheuchzeri in the USA suggests long-term, evolutionarily conservative relationships between the arthropod and fungal communities and their host plant, which may be related to the pattern of reassembly of wetland biomes with similar plant-dominance-diversity structures during successive glacial phases. Collecting DT data from new localities to increase temporal resolution will be necessary to further understand effects of late Paleozoic glacial/interglacial cycles on plant-arthropod and fungal associations.