Climate change could destroy this 100-million year old partnership

For more than 100 million years, a species of spiny crayfish native to eastern Australia and tiny, tentacled flatworms known as temnocephalans have shared a symbiotic relationship, but a newly published study suggests that climate change could soon put an end to the relationship.

Writing in the latest edition of the journal Proceedings of the Royal Society B, lead author Dr. Jennifer Hoyal Cuthill from Cambridge University’s Department of Earth Sciences and her colleagues explained that the temnocephalan flatworms, which depend on the Australian spiny mountain crayfish for sustenance, are in danger of coextinction with their endangered hosts.

The flatworms and the crayfish live in the cool freshwater streams of eastern Australia, Cuthill and her co-authors explained. The flatworms live on the surface or the gill chambers of the crayfish, capturing tiny food particles and helping to remove parasites. However, environmental changes and habitat loss pose a serious threat for the crayfish, and by proxy, the flatworms.

In the study, the authors reconstructed the ecological and evolutionary history of both species using DNA sequences from specimens obtained from throughout eastern Australia. By doing so, they not only were able to recreate the shared evolution of the creatures, but measured for the first time the risk of extinction the temnocephalans face due to crayfish’s endangerment.

Three-fourths of crayfish, 60% of flatworms face extinction

“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,” Dr. Cuthill explained Wednesday in a statement.

The first species of mountain spiny crayfish date back at least 80 million years and the creatures have diversified over time. A “molecular clock” reconstruction of the temnocephalans’ timeline revealed that the flatworms were every bit as ancient as their symbiotic partners, the researchers reported.

The two species have evolved together since the Cretaceous Period, but today, many species of crayfish have much smaller geographic ranges than in the past due to long-term climate warming and drying in the region. These crayfish have been categorized by the International Union for the Conservation of Nature (IUCN) as either endangered or critically endangered, and now the study has shown for the first time that the flatworms face a similar threat level.

“Environmental change” had left “host-specific temnocephalans vulnerable to coextinction with endangered hosts,” the Dr. Cuthill and her colleagues wrote. “Consequently, the extinction of all Euastacus species currently endangered (75%) predicts coextinction of approximately 60% of the studied temnocephalans, with greatest loss of the most evolutionarily distinctive lineages.”

“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,” co-author Dr. Tim Littlewood of the National History Museum in London added. “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.”

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Image credit: David Blair, James Cook University