THE TRACE FOSSIL RECORD OF TREMATODE-BIVALVE PARASITE-HOST INTERACTIONS

Parasitism is one of the most pervasive phenomena amongst modern eukaryotic life and yet, relative to other biotic interactions, very little is known about its history in deep time. As many parasites are small-bodied and lack biomineralized skeletons, we should not expect an extensive record of body fossils, therefore we must also seek evidence for parasitism in the form of traces and malformations on the mineralized hosts. Digenean trematodes (Platyhelminthes) are complex life cycle parasites, which have practically no body fossil record, but induce the growth of characteristic malformations in the shells of their bivalve hosts. Many of these malformations are readily preserved in the fossil record, but, until recently, have largely been overlooked by students of the fossil record. In this talk, we present the various malformations induced by trematodes in living bivalves, evaluate the distribution of these traces through deep time in the phylogenetic and ecological contexts of their bivalve hosts, explore how various taphonomic processes have likely biased our understanding of trematodes in deep time, and evaluate their utility as paleoenvironmental indicators. Trematodes are known to negatively affect their bivalve hosts in a number of ways including castration, modifying growth rates, causing immobilization and, in some cases, altering host behavior making the host more susceptible to their own predators. Digeneans are expected to be significant agents of natural selection. To that end, we discuss how bivalves may have adapted to their parasites via heterochrony. Additionally we will explore how the fossil record of trematodes can inform our predictions for shallow marine and estuarine ecosystems in the context of anthropogenic climate change and sea level rise.