Squids Attract Mates with Stylish Ink: Heart Marks as Love Signals

Feb 14, 2024 | News On Japan

TOKYO - A research group from the University of Tokyo and others has announced that squid, which are known to eject ink to confuse predators and escape, also use the ink in a courtship behavior to make themselves more conspicuous and appeal to females.

This is the first time such courtship behavior has been confirmed, and the research group hopes it will aid in the understanding of the evolution of animal communication.

Graduate students from the University of Tokyo, including Arata Nakayama, focused on a species of squid called the Gonatus squid, observing the males as they courted females by touching them with two special tentacles while ejecting ink. They found that the males would stroke the females with their tentacles for an extended period and emit small blobs of ink before finally spreading ink over a wide area to darken the background and then making their bodies shine white to court the females. According to the research group, this is the first time squid have been observed using ink for courtship behavior. Associate Professor Yoko Iwata of the University of Tokyo's Atmosphere and Ocean Research Institute said, "I was very surprised to find that squid, which have high intelligence, have repurposed ink originally used for escape for courtship behavior. Being able to immediately set the stage when they want to court is a significant advantage and will help us understand the evolution of animal communication."

The Gonatus squid, which measures about 12 centimeters in length, inhabits the sea at a depth of around 50 meters from southern Hokkaido to the Philippines, but its detailed ecology is still not well understood. The Aomori Prefectural Asamushi Aquarium, which was the first to successfully breed this species of squid in Japan, made headlines in 2019 when it captured footage of a male using its short tentacles to form a "heart mark" while courting a female. The latest research findings have come from continued observation, paying attention to the fact that the squid were also ejecting ink while forming the "heart mark" with their tentacles.

Source: NHK

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