Insect Herbivory on Ferns From a Modern Marsh Lowland Locality, Southern Brazil: Implications for Interpreting Fossil Plant–insect Interactions

Abstract

Ferns are a model plant group for comparing insect herbivory between modern and deep time assemblages. We assessed fern–arthropod interactions in a modern marsh to reveal the taphonomic, morphological, and ecological implications of insect herbivory on fossil plant assemblages. Six functional feeding groups—hole feeding, margin feeding, surface feeding, piercing and sucking, galling, and pathogens—are present in eight fern species. We identified a total of 23 distinct damage types (DTs) on ferns, comprising 16 insect-mediated DTs, two of which are newly described in this study, and seven pathogen DTs, including one new addition. Among these, we present six arthropod-induced DTs that were previously undocumented in ferns. Furthermore, we report five DTs with fossil analogs. External foliage feeding, consisting of hole feeding, margin feeding, and surface feeding functional feeding groups, is the principal factor for DT richness on ferns in this lowland locality. We found products of arthropods behavior on ferns, such as instar molts and dead bodies and the byproducts from reproductive processes, which are unlikely to preserve in the fossil record. The taphonomic implications of these arthropod behavioral products are inferred by considering the substances that attach these structures to leaf tissues, potentially enhancing their preservation potential in the fossil record. Relatively mesic conditions support ferns in the lowland locality, resulting in a greater richness of insect herbivory compared to ferns in cooler xeric habitats from a previously surveyed upland locality.