How mantis shrimp make sense of the world25 November 2019

With exceptionally keen vision and the fastest strike inthe animal kingdom, mantis shrimp are formidablepredators of coral reefs around the world. Credit: Roy L.Caldwell/University of California, Berkeley

A study involving scientists at the University ofArizona and the University of Queensland providesnew insight into how the small brains of mantisshrimp—fierce predators with keen vision that areamong the fastest strikers in the animalkingdom—are able to make sense of a breathtakingamount of visual input.

The researchers examined the neuronalorganization of mantis shrimp, which are amongthe top predatory animals of coral reefs and othershallow warm water environments.

The research team discovered a region of themantis shrimp brain they called the reniform("kidney-shaped") body. The discovery sheds newlight on how the crustaceans may process andintegrate visual information with other sensoryinput.

Mantis shrimp sport the most complex visualsystem of any living animal. They are unique inthat they have a pair of eyes that move

independently of each other, each with stereoscopicvision and possessing a band of photoreceptorsthat can distinguish up to 12 different wavelengthsas well as linear and circular polarized light.Humans, by comparison, can only perceive threewavelengths—red, green and blue.

Therefore, mantis shrimp have much more spectralinformation entering their brains than humans do.Mantis shrimp seem to be able to process all of thedifferent channels of information with theparticipation of the reniform body, a region of theanimal's brain found in the eye stalks that supportits two protruding eyes.

Researchers stained mantis shrimp brain specimens withantibodies to obtain highly detailed images showingvarious types of neuronal processes. The reniform body(inset) is connected to the eye's visual (middle- andupper-left) and learning and memory center (small, bluestructure at bottom). Credit: Marcel Sayre/LundUniversity Sweden and Roy L. Caldwell/University ofCalifornia, Berkeley

Researchers Hanne Thoen and Justin Marshall at

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Queensland Brain Institute at the University ofQueensland in Brisbane, Australia, teamed up withNicholas Strausfeld at the University of Arizona, aswell as scientists from Lund University in Swedenand the University of Washington in the U.S. to gaina better understanding of how the reniform bodiesconnect to other parts of the mantis shrimp brainand gather clues to their functional roles.

Using a variety of imaging techniques, the teamtraced connections made by neurons in thereniform body and discovered that it contains anumber of distinct, interacting subsections. Oneparticular subunit is connected to a deep visualcenter called the lobula, which is structurallycomparable to a simplified visual cortex.

"This arrangement may allow mantis shrimp tostore quite high-level visual information," saidStrausfeld, senior author of the paper that waspublished in the Journal of Comparative Neurology.

"Mantis shrimp most likely use these subsections ofthe reniform body to process different types of colorinformation coming in and organize it in a way thatmakes sense to the rest of the brain," said leadauthor Thoen. "This would enable them to interpreta large amount of visual information very quickly."

One of the study's crucial findings was that neuralconnections link the reniform bodies to centerscalled mushroom bodies, iconic structures ofarthropod brains that are required for olfactorylearning and memory.

A close-up of the unique architecture of the mantisshrimp eye. Credit: Roy L. Caldwell/University ofCalifornia, Berkeley

"The fact that we were now able to demonstratethat the reniform body is also connected to themushroom body and provides information to it,suggests that olfactory processing may take placein the context of already established visualmemories," said Strausfeld, Regents Professor ofneuroscience and director of the Center for InsectScience at the University of Arizona.

The discovery of the reniform body, however, is notlimited to mantis shrimp. It has been identified inother species as well, including shore crabs, shrimpand crayfish.

In 2016, an Argentinian group discovered that, incrabs, what are now known as reniform bodies actas secondary centers for learning and memory.According to Strausfeld, this suggests that theformation and storage of memories occurs in atleast two different and discrete sites in the brain ofthe mantis shrimp and likely other members ofmalacostracans, the largest class of crustaceans.In addition to mantis shrimp, malacostracansinclude crabs, lobsters, crayfish, shrimp, krill andother less familiar species that together account for

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about 40,000 living species and a great diversity ofbody forms.

Reniform bodies have not been identified in insectsand may be uniquely crustacean attributes, theresearchers say. Alternatively, they might behomologous to a structure found in insect brainscalled the lateral horn, which sits between the opticlobes and the mushroom bodies. Strausfeld pointedout that fruit fly research done by other groupsshowed that the lateral horn is crucial in assigningvalues to learned olfactory information.

"The hunt is now on to determine if insects have ahomologous center," he said. "If we are looking forhomologs in other arthropods, the reniform bodywould be the obvious candidate."

More information: Hanne Halkinrud Thoen et al,The reniform body: An integrative lateralprotocerebral neuropil complex of Eumalacostracaidentified in Stomatopoda and Brachyura, Journalof Comparative Neurology (2019). DOI:10.1002/cne.24788

Provided by University of ArizonaAPA citation: How mantis shrimp make sense of the world (2019, November 25) retrieved 31 January2022 from https://phys.org/news/2019-11-mantis-shrimp-world.html

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