The mountain spiny crayfish and a species of flatworms called temnocephalans are threatened by extinction, putting their 100 million-year-old symbiotic relationship at risk of ending. Researchers from the UK and Australia blame environmental and climate change for this problem.

The researchers term this as coextinction, the loss of one species when the species it relies on becomes extinct. In this case, when all the endangered mountain spiny crayfish disappear, 60 percent of the temnocephalans will also go extinct.

“We’ve now got a picture of how these two species have evolved together through time,” says the study’s lead author Jennifer Hoyal Cuthill from Cambridge’s Department of Earth Sciences. “The extinction risk to the crayfish has been measured, but this is the first time we’ve quantified the risk to the temnocephalans as well – and it looks like this ancient partnership could end with the extinction of both species.”

The study, published in the Proceedings of the Royal Society B, states that temnocephalans evolved with the spiny crayfish over millions of years. The flatworms reside on the crayfish’s surface or inside the crustacean’s gill chamber where they remove parasites.

To predict the severity of coextinction, the researchers employed computer simulations. However, despite this dismal report, the researchers believe that both the mountain spiny crayfish and temnocephalans can still be saved if their habitats are protected from the effects of environmental and climate change.

“The intimate relationship between hosts and their symbionts and parasites is often unique and long-lived, not just during the lifespan of the individual organisms themselves but during the evolutionary history of the species involved in the association,” concludes Tim Littlewood, the study’s co-author from the Natural History Museum. “This study exemplifies how understanding and untangling such an intimate relationship across space and time can yield deep insights into past climates and environments, as well as highlighting current threats to biodiversity.”