Do giant oceanic manta rays have self-awareness?

Elaborate cognitive skills, which is the processes used to acquire, process, store and use information from the environment, arose independently in different groups of organisms, yet they are very rare! Since most cognitive skills are hard to quantify, another subset of cognition is often measured - self-awareness. This ability implies that animals are able to recognize themselves or their reflection in a mirror (mirror test) as their own and not as another individual's, a necessity to be able to assess one's own place in the world.

During a mirror test, animals may exhibit different behaviors through phases. The first phase is the exploratory or social phase where the animal meets his reflection for the first time, it either contemplates or tries to interact with it, which would imply a lack of self recognition at first sight. The second one is contingency checking, which is an unusual and repetitive behavior used to understand one's own image. This phase is only demonstrated in animals that come to see their reflection as their own during the exploratory phase. The third and last phase is self-directed behavior, for ex. a chimpanzee picking its teeth while using his reflection.

Mirror self recognition (MRS) has been demonstrated in great apes, such as chimpanzees, orangutans, Gorilla gorilla), Asian elephants, bottlenose dolphins, cleaner wrass and the magpie. These animals have large and very foliated brains and have been shown to exhibit cooperative and empathic behaviors. As we saw earlier, MRS is rare.

A team of scientists thought it would be interesting to see if manta rays were aware of themselves. They picked this species because it has a high encephalization quotient (the ratio of brain mass to body size), which is often a sign of intelligence, a very foliated cerebellum and they feed in aggregation, which implies cooperation. However, mirror tests have been very controversial and even more so with fishes: The most common criticism of the mirror test with fish, is that most of them use chemical cues - chemoreception, to recognize other individuals over sight. Yet, this may not be the case with manta rays as they have a large optic tectum and telencephalon, implicated in eye movement and vision.

Manta birostris

Their mirror test setup and methods

Two giant manta rays (Manta birostris), one male and one female were tested. The team is not sure whether the female is also M.birostris, as they say, she has a “white mouth region, brownish back coloration and the lack of large white shoulder bars » but fulfills all other criteria.

The team used a large tank with no obstacle, so that the manta rays could maneuver freely. The tank was 10m wide, 15m long and 5.5m deep. The polygon is the underwater camera and the circle an camera outside the tank.

3 different conditions where set in place. The first one is with the mirror, the second and third ones are controls (no mirror and non reflective whiteboard, which is the mirror but reversed. 7 trials where made for 16 days, 10-15min a day. The video was recorded and viewed by 2 independent analysts. (The results of the first analyst had to be matched by the 2nd one) and an unpaired t-test + standard error (SEM) were performed. As for the parameters taken into account, the variables were the total time spent in the observation area, the number of cephalic fin movements and the circling in the observation area. The onset and duration of behavior was also recorded.

Results and Discussion

What they found out is that these giant manta rays spent more time in front of the observation area and significantly less time when there was no mirror or with the whiteboard. They barely interacted socially with their reflection, just like bottleneck dolphins. This indicates that they didn't perceive themselves as being other individuals. What's more interesting, is their checking contingency behavior. The cephalic fin which was closer to the mirror was moved at a greater frequency, a way for them to explore their own reflection through movement and they also let out bubbles, suggesting self-directed behavior. These results indicates that M. birostris has indeed some level of self-awareness, which is an amazing feat for an animal!

However, one shouldn't forget the bias of this experimental design - the lack of individuals to repeat the test. We should also be cautious because the mirror test only shows a specific level of awareness and doesn't necessarily imply the ability for empathy and other elaborate cognitive skills. Further investigation would be necessary to understand the level of awareness at which the manta ray operates and if other species of elasmobranchs have self-awareness.

- Lifeyard

Sources

Ari C, D’Agostino DP. Contingency checking and self-directed behaviors in giant manta rays: Do elasmobranchs have self-awareness? J Ethol. 2016 May 1;34(2):167–74.