Living in eternal night, sea creatures survive with senses other than sight

SCUBA divers explore underwater cave

Image: Texas A&M-Galveston

Over millions of years, life in the total darkness of underwater caves has blinded many forms of crustaceans. However, some of these creatures have evolved their other senses to deal with the lack of light, says a team of international researchers that includes a Texas A&M University at Galveston professor.

Tom Iliffe, a professor of marine biology, and his German collaborators recently published their findings in the current issue of BMC Neuroscience.

Crustaceans include crabs, lobsters, shrimp and crayfish, among others. The researchers focused on three less-familiar subgroups:  Mictocarididae (from Bermuda), Spelaeogriphacea (from South Africa) and Thermosbaenacea (from Italy).

All three subgroups are blind and their bodies feature small stalks that no longer support eyes.

“These animals first colonized caves at a time when the continents were still connected to each other and most of the world was one big land mass,” Iliffe says “This was at least 180 million years ago, a time when dinosaurs dominated the Earth.”

These crustaceans were forced to undergo “regressive evolution,” in which organisms actually lose body features that go unused. “These small crustaceans have lived underground in total darkness all this time, so there was no need for vision or even eyes,” Iliffe says.

Significant changes evolved in their brains and bodies. Their sense of smell increased. They developed longer antennae and an enhanced nervous system. These changes helped the creatures to obtain food or find mates as they swam or crawled through the caves, the team reports.

Diving in underwater caves from Bermuda, Iliffe was able to capture some of these blind crustaceans for examination.

“Even with no light in the caves, evolution continued to proceed as it always does – these creatures were able to adapt and survive in this totally dark environment, while life on the surface of the Earth changed radically,” he adds. “Our findings suggest that these creatures, as they spent longer and longer time in complete darkness, changed independently during this evolutionary process, and they gradually reduced brain functions that were no longer needed.”

The project was funded by the German Science Foundation and assisted by the Bermuda Biodiversity Project.

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