Palaeontology: Early evidence of parasitism discovered

Animals had to contend with parasites shortly after the Cambrian explosion (approximately 541 million years ago), reports a paper in Nature Communications this week. The study finds that ancient brachiopods were parasitized by an organism that probably diverted the brachiopod’s food to itself. The findings represent the oldest known parasite–host relationship identified in the fossil record to date.

Brachiopods are small shell-like marine animals that resemble bivalve molluscs. There are currently approximately 450 species of brachiopods living, but over 12,000 species are known from the fossil record.

Zhifei Zhang and colleagues analysed a fossil population of the Cambrian brachiopod Neobolus wulongqingensis discovered in Yunnan, China, dating from approximately 512 million years ago. They found that many of the brachiopods were encrusted with a tube-dwelling organism on the outside of their shells. Brachiopods encrusted with tubes were significantly smaller and the tubes were aligned with the brachiopod’s own feeding currents. Therefore, Zhang and colleagues suggest that the tube-dwelling organism was a parasite that reduces its host’s fitness by stealing the host’s food (known as a kleptoparasite).

Parasitic interactions are difficult to document in the fossil record because most inferences have to be made based on appearance. Here, the authors have assembled rare evidence of not only the appearance of parasitism, but a cost of parasitism as well.