Scientists Have Discovered Fossils of World’s Earliest Parasites
Scientists from the Northwest University in China have found evidence of the first-ever parasite — dating back over 500 million years.
Published in the peer-reviewed journal Nature Communications on Tuesday, this discovery documents the oldest known example of a parasite-host relationship. Found in Yunnan, China, the tan-colored outcropping of dense colonies of ocean-dwelling brachiopods (similar to modern day mollusks) clustered, and subsequently fossilized, together. Hundreds of the brachiopods had several tube-like, tapered figures appended to their exterior shells. The researchers believe that the fossils with the tubes on them were infected by the parasites, which were worm-like, filter-feeding animals that were living inside the mineralized tubes.
However, even though fossils are probably the most important source of studying the evolution of different species, they often pose challenges when it comes to the study of parasites and their evolution. For starters, parasites don’t fossilize well because their bodies are often small and soft, the researchers explained. Moreover, a number of parasites live inside the hosts’ bodies, and often decompose too quickly to be preserved through fossilization. In addition, even if two organisms are found fossilized together, discerning whether their relationship was parasitic, or simply symbiotic, poses yet another challenge.
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In this scenario, however, what led the scientists to conclude that the tube-like creatures were, in fact, parasites, were three significant observations: first, the mouth-like parts of the worms were positioned along the open edge of the brachiopods’ shells — hinting that the worms were kleptoparasites, or food-stealing parasites that steal food from the host before it could even be ingested; second, the worms appeared only on brachiopod-fossils, and never alone — indicating that the organism couldn’t survive on its own; and third, the parasite-encrusted specimens were notably smaller than their parasite-free neighbors — suggesting that the worms stole so much food that they stunted their hosts’ growth.
This discovery dates back to about 541 million years ago in the Cambrian period — an important point in the history of life on Earth, when most of the major groups of now-known animals first appear in fossil records. In fact, the diversification of different animal species is also supposed to have taken place during this time. Putting that into context has led the researchers of the present study to conclude that parasite-host relationships are, perhaps, as old as lineages of several animals known to us today.
But, even as the scientists are celebrating the discovery, they lamented on how little we know about the evolution of parasites today. “Many questions still remain. Perhaps the most important is how parasitism first evolved. We know parasitism has evolved multiple times, and almost every animal group includes one or more parasites. There are even parasitic mammals… [Also] we still don’t know how common parasites were in the past, or what innovations in life’s history occurred due to biological pressures exerted by parasites. Because of this, identifying if parasitism is the cause of major evolutionary changes remains an ongoing challenge,” co-authors of the study, Luke C. Strotz and Glenn A. Brock, wrote in The Conversation.