Coral-Infecting Parasites in Cold Marine Ecosystems

Abstract

Corallicolids are apicomplexan parasites that infect a wide range of corals and related anthozoans. Current global environmental sequencing shows corallicolids are tightly associated with coral reef environments, but this sampling is potentially biased against common parasitic strategies, which might lead them to go unnoticed in environmental surveys. We tested the global distribution of corallicolids using a more focused strategy, by specifically targeting potential anthozoan host animals from cold/temperate marine waters outside the coral reef context. We find that corallicolids are in fact common in such hosts, in some cases at high frequency. Infection was confirmed with fluorescence microscopy, which also shows tissue specificity similar to that observed in hosts from topical coral reefs. Amplified sequence variants from cold water environments suggested these parasites are genetically distinct from reef-associated parasites. We tested whether this reflects host- or environmental-specificity with phylogenetic analysis of full-length rRNA genes. Parasites of coral reef-dwelling anemones were found to be related to parasites of cohabiting corals, while cold-water anemones and corallimorphs were genetically distinct, and more closely related to parasites of tropical Pacific hosts, altogether suggesting biogeography is an important factor for parasite evolution. Overall these results greatly expand the range of corallicolids beyond coral reefs, and also illustrate significant blindspots that result from strategies commonly used to sample microbial biodiversity.

Keywords: Coral, parasite, apicomplexan, evolution, ecology, anthozoa