PHANEROZOIC PARASITISM AND MARINE METAZOAN DIVERSITY: INCREASING RISK WITH SUPPORT FOR THE AMPLIFICATION HYPOTHESIS

Growing evidence suggests that biodiversity mediates parasite prevalence in modern ecosystems. The opposing amplification and dilution hypotheses predict positive and negative relationships between parasitism and diversity, respectively, but how have these relationships played out through deep time? We have compiled the first global database on occurrences and prevalence of marine parasitism throughout the Phanerozoic to address these questions. We recorded 2,118 species occurrence observations from the published literature ranging in age from Cambrian to Holocene, of which, we interpret 1,424 to unambiguously represent parasitism among nine host phyla and 12 parasite phyla. The number of parasitism occurrences increased step-wise between the Paleozoic, Mesozoic, and Cenozoic. Median prevalence values by Era are 5% for the Paleozoic, 4% for the Mesozoic, and a significant increase to 10% for the Cenozoic. We calculated Period-level shareholder quorum sub-sampled (SQS) estimates of mean sampled diversity, three-timer (3T) origination rates, and 3T extinction rates from the Paleobiology Database for the most abundant host clades to compare to both occurrences of parasitism and the more informative parasite prevalence values. Generalized linear models (GLM) of parasitism occurrences and SQS diversity measures support both the amplification (all taxa pooled, crinoids and blastoids, and mollusks) and dilution hypotheses (arthropods, cnidarians, and bivalves). GLMs of prevalence and SQS diversity measures only support the amplification hypothesis (all taxa pooled and mollusks). Though likely scale-dependent, parasitism has increased through the Phanerozoic and clear patterns primarily support the amplification of parasitism with biodiversity in the history of life.