Insect Associational Dynamics Ninety Million Years Before Angiosperms: Questions, Approaches and Preliminary Methods

Insects entered into relationships with land plants at approximately 410 Ma, forming the first of four major associational phases. This mid-Paleozoic event was surpassed by the expansion of modern types of herbivory during Phase 2 in the Late Paleozoic, ending with the end-Permian extinctions. Recovery after the extinction aftermath constitutes the third major phase of herbivory expansion, commencing modestly during the Middle Triassic in Laurasian and Gondwanan localities and reaching its acme during the Late Triassic in the Molteno Formation of South Africa's Karoo Basin. Our preliminary analyses of this abundant, diverse and well preserved biota—representing 106 stratigraphically ordinated localities, 7 geographically widespread habitats, 79 diagnostic insect/mite damage types (DTs), about 220 whole-plant taxa, and 177,301 examined leaf, seed, stem, and other organ specimens—has established the best fossil-record case for testing hypotheses of how plant and insects associate and evolve in deep time. From Molteno data, the following questions will be addressed: Do stereotyped plant-insect associations or combinations of associations characterize particular plant hosts and their habitats? Do dominant plant taxa and their herbivore component communities, evidenced by their DT spectra, evolve within habitats or among habitats? Is there gradual replacement of generalized DTs by host-specific DTs, perhaps accompanied by the partitioning of tissues within plant organs and the colonization of new plant taxa? What insect herbivore clades dominated this exceptional diversification onto horsetail, fern, and seed-plant host clades 90 m.y. before the angiosperm appearance that characterized the fourth major phase of herbivore expansion? Such questions will be addressed by a several million-year-old, internally well resolved, basin-wide record that will provide tests of hypotheses developed from modern plant-insect associational theory. We will document the timing, interspecies associations, autecological and synecological scope, and community structure of plant-insect associations during this circumscribed interval of deep time.