The impact of bacterial activity on decay and fossilization of arthropods: An experimental approach

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Arthopods represent the highest biodiversity among metazoa. Insights into evolution and phylogeny of arthropods are mainly derived from exceptionally well-preserved fossils from so called conservation deposits (Konservatlagerstätten). These fossils were formed by a complex sequence of biological, chemical and geological processes that starts immediately after the death of the organism. Between the death and the embedding of the carcass into the sediment, decay (aerobic) or/and putrefaction (anaerobic)- catalyzed by microorganisms that originate from the gut flora of the arthropod and/or its environment – may lead to a partial loss of characteristic features that are important for phylogenetic interpretations. This bacterial decay, which is not equally fast in different tissues, has led to serious misinterpretation in the fossil record of vertebrates, because fossils of partially decomposed organisms were incorrectly classified. In addition to the decay of organisms, bacteria have also been shown to contribute to the formation of fossils, by synthesizing biofilms which later fossilize by precipitation of minerals and yield casts or pseudomorphs of the hard and fine tissues of the carcass. Also the precipitation of minerals may be a product of bacterial activity.The overall goal of this project is to improve the general understanding of decay processes in the context with microbial activity in arthropods. To this end we will start monitoring the disarticulation of whole arthropods and characterize the developing microbial communities on the carcass over the time. The goal of the decay monitoring will not only be to observe the physical disarticulation, but also to understand the influence of chemical and physical parameters and to identify the best conditions for mineralization. The microbiome of decaying arthropods under different environmental conditions will be characterized by 16S rRNA sequencing and correlated to its sources (gut, environment), the speed of the decay and morphological changes. On the other hand, bacterial strains which are characterized by the production of biofilms and exoenzymes will be isolated from the decaying cadavers and characterized. To prove or disprove the hypotheses that the formation of biofilms favors the formation of fossils, and that on the other hand the secretion of exoenzymes, however, leads to an accelerated degradation, different tissue types of arthropods will be incubated with the isolated bacterial strains in the second part of the project. Decay or fossilisation will be recorded and yield systematic insights into the influence of bacterial activity on the fossilisation process. Thus, finally the experiments shall contribute to a better understanding of the conditions that determine the occurrence of exceptional preservation of arthropods in different environmental settings through geological time.