Earliest Fossil Evidence Of Parasite-Host Relationship Discovered In China

Depiction of tube-dwelling parasites occupying the external shell of Neobolus wulongqingensis. Zhifei Zhang (Northwest University)

Rachael Funnell 02 Jun 2020, 16:00

The earliest known fossil evidence of parasitism has been uncovered by a team of scientists working in Yunnan, China. Described in Nature Communications, the specimen reveals that this kind of host-parasite symbiosis was taking place shortly after the Cambrian explosion around 154 million years ago.

Parasitism describes the relationship between species whereby one organism, the parasite, hitches a ride on or inside another organism known as the host. Examples can be seen in humans where tapeworms (some 10 meters in length) will occupy our digestive systems (and other areas) sapping us of sustenance and damaging our organs.

The example of parasitism discovered by the team working in Yunnan occurred between a brachiopod, a small shelled animal that looked a bit like a clam, though the two are not closely related, and some kind of tube-dwelling organism. The researchers noted that fossil specimens of the Cambrian brachiopod Neobolus wulongqingensis were encrusted with tiny tubes that all lined up conveniently close to where the brachiopod’s own feeding currents would suck in sustenance.

One of the specimens examined by Zhang and colleagues. Zhifei Zhang (Northwest University)

Given the minute size of the tubes and their specific occurrence near feeding currents, lead author on the study Zhifei Zhang and colleagues concluded that the tube-dwelling organism represented a parasite. These tube-dwelling kleptoparasites hitched a ride on the shell of brachiopod, weakening its chances of survival by stealing its food. 

 

Examples of kleptoparasitism in extant species include dung beetles that will steal from the stocks of the Scarab dung beetle, which spend their lives relocating vast amounts of vertebrate dung to establish their nests. The behavior benefits the beetle thieves as they can focus on rolling or tunneling without having to waste time going out looking for precious poop.

A recreation of the brachiopod sporting the parasitic tube-dwelling organisms on its shell. Zhifei Zhang (Northwest University)

Examples of parasitism aren’t easy to spot in the fossil record as many examples, such as the dung-stealing beetles, can only be confirmed based on observable behaviors. Therefore, all parasitic interactions known from the fossil record are reliant on the specimens and their ability to communicate not just the appearance of the parasite but also the cost to the host. Zhang and colleague’s discovery of the food-thieving, tunnel-dwelling, brachiopod-depleting organism represents the oldest known parasite-host relationship identified in the fossil record to date.

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