Here's looking at you: Australian freshwater crayfish may commit details of each other's faces to memory.
Credit: NSW Department of Primary Industries
SYDNEY: They may not be pretty, but the faces of Australian crayfish are apparently memorable. New research shows that these invertebrates are able to recognise each other's faces.
"This is a remarkable capacity for an invertebrate species," said zoologist David McMillan from the University of Melbourne in Australia. "Yabbies remember the smell of other crayfish, but the extent to which they remember visual features has previously been unknown."
Visual cues
McMillan made the discovery by marking the heads of freshwater crayfish of the species Cherax destructor – known as yabbies in Australia – with correcting fluid. His team's results are published in the journal PLoS ONE.
Many social invertebrates, such as bees and wasps, have good visual memories, which assist in the smooth running of their colonies, but invertebrates have never been known to recognise each other by their faces as humans do. The ability was further unexpected in the yabby, which is a creature with little social cohesion.
To test how the animals remembered one another, McMillan's team dabbed spots of yellow correcting fluid onto the faces of pairs of the crayfish, and allowed them to fight – as is customary when individual yabbies encounter each other for the first time.
Subsequently, the loser was presented with both the yellow-marked winner, and an unfamiliar, unpainted yabby. Time and time again, the loser would gravitate towards the earlier rival – but only when the marker had been dabbed on its head, not anywhere else.
Dear enemy
By choosing to confront an adversary they have already fought, the animals benefit from experience and are less likely to suffer injury at the hands of an unfamiliar combatant, write the researchers – a strategy known as the "dear enemy" phenomenon
McMillan said that the study reveals the face as the key area which the animals commit to memory for recognition. He believes that variations in features such as the eyes and width of the face are used to make a judgment.
"[This] outcome strengthens recent evidence that crustaceans have true individual recognition… a controversial topic for the past 30 years," write the researchers. It also "calls into question whether recognition evolved in invertebrates, to be further developed in vertebrates, or whether two different processes are involved."
Memories
Hello, I am writing from California. During the years of 2005, and 2006, I spent weeks rescuing Mourning Cloaked Butterfly Caterpillars. In the late afternoon, they left their Cypress tree on the Pacific Coast Highway, and had to make a quick run of about 100 Ft. on sizzling hot asphalt during traffic. If they missed our driveway, they had to cross another busy street to the small park at the Ocean. Many of them I had hanging from my bedroom ceiling for over a week (attached to paper egg cartons. When the cocoon was completely black (the color of the Butterfly), I pinned the carton outside of my bedroom window in the small garden. One morning I had seven beautiful Butterflies hanging upside down, waiting for their wings to dry so they could take flight. The second year, I rescued over 40, and most of them survived. They just didn't have the strength to crawl to the over-hang on the porch after being on the hot street. If they didn't make it within a certain time, they would have to spin their cocoon from the first little place on the ground they could find. Usually this was a meal for a Spider.
More than once, when I came out to the garden, they would fly around my face very close, many times, in small circles. I always talked to them from Caterpillar, to Pupae, to Butterfly stage. When they would land on me, it was no surprise. I did have a wasp land on my nose, and just look at me one day also.
Recognize.... faces?
Isn't it possible that the results could easily be interpreted differently, such as that yabbies have an aggressive tendency towards yellow things (as an example)?
If, as the article opens with, yabbies really have been shown to "recognize" each other's faces, why didn't the loser continually fight their prior rivals when they didn't have dots? Since they have no noticeable preference for choosing which yabby to fight when there are no dots, wouldn't that show they don't recognize faces?
Maybe something about the yellow makes the dotted yabby seem weak or injured, and hence an easier fight. No face recognition.
Yep, they recongise faces
Hi there,
The yellow correction fluid experiments were really just phase one in the research, used to show the general area that the yabbies were recognising (when the yellow markings were on the claws, for example, the yabbies weren't particularly interested). On the surface it may seem like yellowness played a role, but as the experiments progressed this was shown not so much to be the case - the later observations in fact used no yellow markings at all; the yabbies were only distinguishable by variations in facial characterisitcs, such as width of the face.
When no yellow dots were present, the yabbies did indeed continue to pick out their previous rivals based on what the researchers believe to be facial recognition.
Hope this clears things up.
Controls
Hi there,
I didn't read the actual paper but I have a few questions. If the yabbies indeed recognize each others face, why to use the color? Why not to keep track of which opponent in being introduced and see whether the fighter would choose always the "dear enemy" again and again?
Second, I believe that the best control would be to, instead of introducing an unknown unpainted opponent, to introduce an unknown opponent painted with a different color, or even an opponent painted with the same color but with a different pattern.
Were these controls performed in the published work? It is not clear from this text and it seems obvious points for me to sure I have unbiased conclusions.