Mantis Shrimp Use Chemical and Visual Cues When Sizing up Opponents

Researchers have found that mantis shrimp rely on a mixture of visual and chemical signals when deciding whether or not to fight. When these signals are manipulated, mantis shrimp change their level of aggression towards opponents. The findings are in a study just published in the journal Royal Society Open Science.

Mantis shrimp, also known as stomatopods, are marine crustaceans that spend most of their lives in burrows. They are fierce predators and use their large claws to kill prey. Mantis shrimp are so strong that they’ve been known to break aquarium glass. They are also territorial, aggressively defending their homes from intruders. During threat displays, they show off their colorful meral spots. In some species, meral spots reflect UV rays but the function of this feature was unknown.

Researchers from the Tufts University’s Graduate School of Arts and Sciences collected wild Neogonodactylus oerstedii, a stomatopod species known for their ability to see UV light. In one experiment, the researchers dipped the stomatopods’ antennae in freshwater to dull their ability to sense chemicals. In a second experiment, the team painted sunscreen over the meral spots of some of the stomatopods. For both experiments, the researchers paired mantis shrimp together to observe their behavior.

When the stomatopods lost their ability to detect chemical cues, they were quicker to approach the burrows of other mantis shrimp. They also showed less aggressive behaviors. The authors believe that they normally use chemical signals to determine whether or not an individual is a threat.

On the other hand, the use of the sunscreen heightened aggressive behaviors. When a mantis shrimp faced an opponent who had their meral spots covered, they acted much more aggressively towards that individual. The lack of UV reflectance seemed to signal that the opponent was less of a threat. The researchers speculate that UV reflectance highlights the meral spots during a threat display. If an individual has their spots covered up, they seem less threatening.

This was the first recorded case of mantis shrimp using a combination of complex signals when deciding whether or not to fight. Chemical and visual cues help stomatopods avoid fights that they’d be likely to lose. Individuals with high levels of UV reflectance in their meral spots appear more threatening to opponents. These types of signals help mantis shrimp defend their homes while avoiding impossible fights.

REFERENCE

Amanda M. Franklin et al. Multimodal signals: ultraviolet reflectance and chemical cues in stomatopod agonistic encounters. Royal Society Open Science (2016).

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