Theodore Holmes, “A Bite Taken Out of Geologic Time: An Experimental Investigation on Decay Induced Changes of Insect Damage Morphology on Leaves”
Mentor: Victoria McCoy, Geosciences
Poster #62

The diversity and abundance of insect damage on fossil leaves is considered to be a good measure of the diversity of ancient insect herbivores. Insect damage, on both modern and fossil leaves, is defined and categorized based on its morphology; however, it is not yet fully understood to what extent this morphology changes during decay and fossilization. If decay and fossilization processes do alter the morphology of insect damage, then analyses of fossilized damage could be biased by these effects, resulting in a skewed interpretation of ancient herbivorous insects. Previous research has not addressed this important question. Here we use decay experiments to investigate the morphologic changes to damaged leaves over time. We simulated insect damage on leaves of the common buckthorn tree (Rhamnus cathartica), by punching holes of two shapes (circles or elongate ‘slots’) in two areas of the leaves (on the margin or lamina). We ended up with one control group and four treatment groups, each with 8 replicates. The leaves were then placed in petri dishes and covered with a small amount of river sediment and water. We observed and photographed their decay over the course of 6 months. Morphological changes were assessed using the Guide to Insect (and Other) Damage Types on Compressed Plant Fossils (Version 3.0 – Spring 2007) to evaluate how our simulated damage would be categorized initially, and to determine how and if this categorization changed after six months of decay. We found that the morphology of insect damage changed through the decay process. Our results suggest that some caution should be taken when applying current morphological categorizations of insect damage to fossils, since decay patterns can alter the appearance of ancient insect bites. We anticipate these findings to be the starting point for additional detailed and focused research, and to enhance our interpretations