Sensing a place in the ocean

Vent shrimps’ brains have large regions that they can use to integrate sensory input, and may also use to orient themselves in their lightless environment.
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The vent shrimp Rimicaris exoculate. Image credit: Magali Zbinden (CC BY 4.0)

Oceanic vents are areas where hot gases and liquids emerge from cracks and chimneys on the seafloor. These fluids can be as hot as 350°C and are rich in potentially toxic chemicals. Nevertheless, they are the key energy source of many animals that make the vents their home. Vents can be found thousands of meters under sea level, where no sunlight penetrates, so the animals living there must use senses other than vision. As an example, the vent shrimp Rimicaris exoculata, which is used as a vent model animal, was thought to orient itself by sensing chemicals in the vents through their sense of smell.

Machon et al. investigate whether vent shrimps possess particular abilities to detect the chemical landscape of the hydrothermal environment, and describe the brain structure and associated sensory systems of R. exoculata. Since the brain in these shrimps is subdivided into regions devoted to different functions, if one of their senses were used more than the others the region devoted to this sense should be bigger or structurally different.

When the anatomy of the brain centers in R. exoculata was compared to that of its shallow-water relatives, there was no suggestion that the vent shrimps had an advanced ability to sense chemicals. Rather, a striking feature of the brain of the vent shrimps is the volume and structure of their higher brain centers, which integrate all of their sensory information. It is possible that these regions are also involved in other brain functions as well, since they take up an especially high proportion of the brain. Machon et al. found similarities between R. exoculata and other crustaceans that have sophisticated navigation skills so they hypothesize that integrative brain centers in vent shrimps could play a role in place memory.

The findings provide new insights for biologists studying animals associated with deep hydrothermal vents and are also important for neuroscientists interested in brain function and evolution. Future studies should focus on senses of the vent shrimp other than smell to ultimately understand the lifestyle and long-term survival of vent animals.