One important consideration in the use of historic AZ PFKFB3 26 sediment DNA is the potential for DLPC fragmentation and degradation. Typically, the best environmental conditions for DNA preservation are cold, anoxic sediments. The conditions of sediment in Kolbotnvannet do not completely meet these conditions, however, DNA was recovered in our study for both Planktothrix and chytrids in fragments of at least 137 base pairs in length. Previous research using cyanopeptoline ociB gene cluster, used in both studies, indicated that 161 bp fragments could be recovered from sediment in this region of Norway as far back as 80�C150 years, depending on the sediment conditions. Therefore while it is possible that not all DNA deposited was recovered from the Kolbotnvannet sediment, comparing the recovered DNA from each chytrid and Planktothrix strain to each other reduces the direct effects of fragmentation. During the early phase, between 1979 and 1990, Kolbotnvannet had high nutrient concentrations and eutrophic lake conditions. During this time, the sediment data showed that two Planktothrix variants had a stable coexistence. Monitoring data indicates that this period of high nutrients gradually decreased and the lake entered a second period of moderate nutrient levels and deepening secchi depth between 1995 and 2013. During this later phase, the sediment data indicate a steady increase and dominance in chemotype 1 DNA concentrations, while at the same time chemotype 9 DNA remained low and stable. At no time did chemotype 5 or 7 appear. These results allow us to compare the sediment data with the laboratory results of De Bruin et al. where parasitic pressure drives diversity. As nutrients began to decline in the 1990s, Planktothrix chemotype 1 began to increase relative to chemotype 9 while at the same time chytrids continued to remain stable relative to the chemotype. By 1995 chemotype 1 in Kolbotnvannet began a period of domination that lasted more than ten years. We hypothesized that if the chytrid�� host interaction followed the hypothesis of De Bruin et al. during the period where a single chemotype dominated in Kolbotnvannet, chytrid fitness should have increased rapidly after a short adaptation lag to completely remove chemotype 1, or to return to the conditions in the early phase. According to the work of De Bruin et al., a dominant single genotype host would present the chytrids with a much smaller, simpler set of parameters, which would result in increasing parasite DNA concentrations and limiting the dominant host. Our results from the sediment DNA did not follow this prediction, but to the contrary indicated that chemotype 1 was dominant over chemotype 9 in the presence of chytrids for an extended period of years. This period represents a much longer time frame than the 200 generations found by De Bruin et al. to be required for the chytrid and single diatom shift.