DIVERSITY, BIOGEOGRAPHY, BODY SIZE AND THE FOSSIL RECORD OF PARASITIC FORAMINIFERA

The evolutionary history of most host-parasite relationships is obscure mostly because parasites are soft-bodied. Foraminifera, however, have an excellent fossil record dating back to the Cambrian. They are significant members of marine habitats and have diverse trophic modes such as suspension feeding, predation and parasitism. Foraminifera could provide an untapped resource for studying host-parasite relationships through time, yet we know little about the diversity and ecology of parasitism in these important protists. Here, we examined the diversity, biogeography, body size relationships and fossil record of parasitic and suspected parasitic foraminifera. Foraminiferal parasites take nutrients directly from the host and have specific behavioral mechanisms to obtain those nutrients. Suspected foraminiferal parasites have life cycles or ecologies that are not well known, but have unusual behavior in relation to their presumed host. Of the >4000 benthic foraminiferal species, 8 (0.20%) are parasitic and 15 (0.56%) are suspected parasites. Eighteen of these bioerode their hosts, but only four trace fossils are known, leaving ~14 traces that await discovery in the fossil record. Foraminiferal parasites are more diverse in tropical, shallow-water regions, but the best known live in cold-water habitats of the North Atlantic and Antarctica. Endo- and ectoparasitism is common, followed by kleptoparasitism and hermit endoparasitism. Body size comparisons for parasitic foraminifera indicate that (1) few are larger than most benthic foraminifera; (2) most are larger than their free-living relatives; (3) most are smaller than their metazoan hosts; and (4) some are roughly similar in size to their protistan hosts. Suspected and parasitic foraminifera occur in the Mesozoic, but most evolved in the Cenozoic. One Cretaceous species has the longest host-parasite relationship ever recorded: 18 Myr. With their broad geographic distribution and fossil record, parasitic foraminifera and their hosts provide essential models to study how climate and environmental change affect multispecies interactions and ecosystem function in modern and fossil communities.