A sea cucumber that lives in extreme deep-sea environments has had its genome sequenced. This聽revealed that many of its genes have been altered, potentially by the聽intense places it calls home.
Chiridota heheva is a sea cucumber, a worm-like animal in the echinoderm group that also includes starfish. First described in 2004, it is one of the only echinoderms that lives in three of the most extreme ocean locations: hydrothermal vents, cold seeps rich in carbon-based chemicals like methane, and 鈥渨hale falls鈥� 鈥� the sunken corpses of whales. These places have little dissolved oxygen and are toxic to many organisms.
To find out how C. heheva survives, researchers led by Muhua Wang at Sun Yat-sen University in China read its DNA from samples collected by team member Jian He in the South China Sea in 2019.
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The team found that 27 genes had been strongly selected for, suggesting they evolved in response to environmental pressures. Four of them are known to be involved in surviving a lack of oxygen.
Some genes had also been duplicated. There were seven genes for aerolysin-like proteins that are usually part of the immune system. Most echinoderms have either just one or none of these.
These proteins create small holes in the outer membranes of bacteria, destroying them. However, Wang says cold seeps don鈥檛 normally have any infectious bacteria. 鈥淲e don鈥檛 think it鈥檚 related to the immune system,鈥� he says.
The sea cucumbers could instead use the proteins to help digest bacteria. This would make sense because, unlike most animals in these environments, C. heheva doesn鈥檛 have symbiotic bacteria that provide it with nutrients. However, Wang emphasises that this idea is only a hypothesis at present.
bioRxiv
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