HOLOCENE RECORD OF TREMATODE-BIVALVE INTERACTION IN REGRESSIVE BACK-BARRIER SETTINGS OF THE PO PLAIN (ITALY)

Elucidating the history of biotic interactions in the fossil record has been a primary theme in paleobiology during the last decades. The majority of this pursuit has been the examination of the activities of predators, and has highlighted the likely role of antagonistic interactions in shaping macroevolutionary trends. However, the role of parasite-host interactions in deep time has not received comparable systematic treatment. Parasitism is one of the most pervasive phenomena amongst modern eukaryotic life and, by contrast, only a minority of studies are known about it in deep time. Here, looking for trematode induced pits, we surveyed >3,000 valves from cored Holocene back-barrier (freshwater to brackish) regressive deposits of the south-eastern Po coastal plain (Northern Italy). The results are contrasted against previous investigations that focused on more distal, shallow marine (shoreface to offshore transition) deposits from the same area. As in previously (and more distally) investigated deposits, preliminary results indicate that digenean trematodes are selective parasites in terms of host taxonomy and host body size. Indeed the bulk of trematode traces were recovered in Abra segmentum: a shallow infaunal siphonate bivalve. Furthermore, as in previous investigations, trematode distribution was environmentally restricted, primarily recovered in lagoonal paleoenvironments with a peak in inner lagoonal settings. Trematode prevalence is higher in lagoonal settings than in lower shoreface settings. Such studies of trematodes prevalence and its millennial scale dynamics are also of basic importance to providing a reference system for evaluating severity and significance of anthropogenic changes in such environments.