They have been evolving in step with each other for around 100 million years, when the mighty Argentinosaurus still shook the Earth, and pterosaurs still ruled the sky. But the symbiotic relationship forged between a species of crayfish and tiny flatworms native to Australia could soon be about to end, as the crustaceans are at risk of extinction due to habitat loss and climate change.
If the mountain spiny crayfish, which live in the cool, freshwater rivers and streams of eastern Australia, is allowed to disappear altogether then it would be an example of coextinction as the tentacled worms that depend on them live nowhere else in the world. While the crayfish feed upon organic matter in the streams, the little worms, known officially as “temnocephalans,” live on the surface of the crustaceans and even in their gills, feeding off even small particles in the water column.
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The researchers traced the history of the relationship between the two species by taking DNA samples from both from populations throughout eastern Australia. From this, they were then able to compile an evolutionary tree for the 37 species of spiny crayfish, and 33 varieties of temnocephalans, and found that the two creatures had deep evolutionary roots. In fact, it seems that they have been evolving side by side in an equal symbiotic relationship for at least 80 million years, but potentially as long as 100 million years during the Cretaceous.
“We've now got a picture of how these two species have evolved together through time,” explains Dr. Jennifer Hoyal Cuthill from Cambridge's Department of Earth Sciences, lead author of the paper examining the evolutionary history and extinction risk of both species in the Proceedings of the Royal Society B. “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 worms live attached to the shell of the crayfish, filtering out organic matter from the water. David Blair/James Cook University
The sometimes colorful crayfish are found in small, isolated pockets of mountain rainforest, with highly restricted ranges, particularly in the state of Queensland. It is for this reason that they are at an incredibly high risk of extinction, as their habitat has been reduced and fragmented over the past millions of years due to changing climates. Coupled with the habitat destruction by humans, and the rapid increase in climate change, 75 percent of the crayfish species – and thus the flatworms that depend on them – are considered endangered or critically endangered.
With the crustaceans playing an important role in the management of the rainforest streams, recycling the organic matter that falls into them, the loss of the crayfish could impact the health of the ecosystem. But more than that, it could also mean the loss of another species entirely. “The temnocephalan worms associated only with these crayfish are also diverse, reflecting a long, shared history and offering a unique window on ancient symbioses,” said Professor David Blair, the study’s senior author. “We now risk extinction of many of these partnerships, which will lead to degradation of their previous habitats and leave science the poorer.”
Main image: Tatters/Flickr CC BY-SA 2.0
