Leaf functional traits, insect herbivory, and fungal damage on early Eocene leaf compression fossils, Dolus Hill, Wyoming

Premise

In the fossil record, herbivory and fungal damage can be directly measured. Though herbivory is commonly recorded, only rarely has it been examined with fungal damage and through the lens of functional plant traits. Here, we introduce, date, and use a new well-preserved fossil flora to understand relationships between fungal damage, insect feeding, and leaf traits during a hothouse interval.

Methods

We constrained the age of Dolus Hill using uranium-lead radioisotopic dating of zircons from tuffaceous sandstone. We identified 611 eudicot leaf fossils, quantified insect feeding and fungal damage, and measured leaf traits on appropriate fossils. Generalized linear models, beta regressions, and Fisher's exact test were applied to elucidate relationships between damage and leaf traits.

Results

Dolus Hill was dated to 52.22 ± 0.21 (95% confidence) million years ago and has 18 eudicot morphospecies. Insect damage occurred on 82% of leaves, and 27% had fungal damage. Leaf mass per area had no relationship with any damage metric; leaf vein density had a positive relationship with the number of damage types on a leaf. Percentage area damaged and fungal damage were not affected by these leaf traits. Fungal and insect feeding damage significantly co-occurred.

Conclusions

The leaf fossils at the Dolus Hill from the Early Eocene Climatic Optimum provide new insight into plant–fungus interactions and the utility of certain plant trait metrics in the fossil record. These insights will enhance our understanding of plant–fungus–insect interactions within the regime of current rapid climate change.