Multitrophic interactions in a geothermal setting: Arthropod borings, actinomycetes, fungi and fungal-like microorganisms in a decomposing conifer wood from the Jurassic of Patagonia
Abstract A permineralized araucarioid conifer stem, preserved in state of partial decay, is described from the Middle to Late Jurassic Chon-Aike Formation (Bahia Laura Group) at Laguna Flecha Negra, in the Deseado Massif, Santa Cruz Province, Argentina. The tree-stem, which comprises periderm to the secondary xylem, shows evidence of interactions with xylophagous borers, fungi, actinomycetes and other fungal-like microorganisms. In the secondary phloem, it displays rows of traumatic resin ducts, which host abundant mycelium comprising very thin hyphae differentiated into spore-producing structures comparable to actinomycete bacteria and spherical fungal-like resting structures. In the cortical and phloem regions, there are cell groups with structural changes, which appear variably degraded by fungi. The secondary xylem displays decay of cellulose and lignified components, at various spatial scales, comparable with fungal decay patterns in modern wood. Further septate fungal filaments, sometimes bearing clamp connections are associated with decayed regions. The degraded secondary xylem shows circular to oval borings filled with frass containing degraded tracheids, comparable to those bored by different wood boring beetles. Development of traumatic resin ducts in the phloem could have been triggered by penetration of the living stem by these xylophagous arthropods. The association of the different components present suggests pathogenic and saprotrophic interactions promoting decomposition of the stem, and represents a rarely-documented example of multitrophic biological interactions involving several different biological groups in Jurassic terrestrial paleoecosystems.