How life in the dark changed crustacean brains

Above, a related type of crustacean called an amphipod. (Credit: Bathyporeia elegans by Hans Hillewaert Wikimedia Commons)

Over millions of years, some forms of crustaceans have adapted to living in the total darkness of underwater caves.

While their eyes have become useless and disappeared, their other senses have evolved to compensate for the lack of sight, says researchers.

The team examined cave-dwelling crustaceans—the group including crabs, lobsters, shrimp, and crayfish among others—but focused on three lesser known subgroups: Mictocarididae (from Bermuda), Spelaeogriphacea (from South Africa), and Thermosbaenacea (from Italy).

What all three have in common is that they are blind, and have only small stalks where their eyes used to be.

blind crustacean
The blind Mictocaris halope, which lives in a Bermuda cave, has learned to adapt to darkness. (Credit: Peter Parks)

“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,” explains Tom Iliffe, professor of marine biology at Texas A&M University at Galveston.

“This was at least 180 million years ago, a time when dinosaurs dominated the Earth. Since then, these small crustaceans have lived underground in total darkness all this time, so there was no need for vision or even eyes.

“Thus, they were forced to live without sight, and they are still living like that today. It’s what is known as ‘regressive evolution’—when evolutionary processes go in reverse and body features are lost due to non-use.”

Changing brains

So how did the lack of light affect the structure and organization of their brains?

Iliffe says that without light, the creatures were forced to adjust, losing not only their eyes, but also having major changes to their brain and nervous system.

“Their olfactory lobes which control the sense of smell and taste were enhanced and became better developed as they lost their vision,” he notes. “As their optic nerves were disappearing, their other senses were taking over. In other words, the changes in their environment changed these crustaceans themselves.”

Enhanced adaptations such as longer antennae and an improved nervous system helped these creatures to obtain food or find mates as they swam or crawled through the caves, the team reports.

[related]

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.”

Iliffe and fellow researchers from Germany report the findings in BMC Neuroscience.

The German Science Foundation funded the project, with which the Bermuda Biodiversity Project assisted.

Source: Texas A&M University