|Posted on 22 March, 2019 at 0:00|
The octopus is curious, crafty and clever and their intriguing behaviour is changing the way we think.
Looking down to the shallow sea grass beds, it was hard to focus. Then I saw it, almost impossible to see, a tiny pygmy octopus. It hid shyly behind a rock eyeing me suspiciously. Hovering above it, with surprise I realised I was also being intently studied.
There are 300 species of octopus around the world. In Sulawesi, at the centre of their diversity, two stand out as octopus celebrities; the wunderpus (Wunderpus photogenicus) and the mimic octopus (Thaumoctopus mimicus). Both were first found in the rich seas of Sulawesi, are well known for their remarkable shape changing abilities and bizarre mimicking of other species.
Some years back another Sulawesi octopus made the news; the coconut stealing octopus. It is the first case of tool use in invertebrates. Octopuses are an intriguing group. They have a reputation for being intelligent, almost mythically so. Scientists have long known they can solve complex puzzles, navigate through mazes, are masters of disguise and more recently have found they accurately mimic other species.
Some go further to say they have personalities even engaging in play. They do things, which normally; we would only expect vertebrates to do.
Masters of disguise
Research, on the so-called mimic octopus, has revealed some intriguing behaviour opening further questions about invertebrate learning and behaviour. Undescribed until 1998, the mimic remains something of a mystery to science. It is a showcase for one of nature’s most remarkable abilities. Here is an animal that can accurately impersonate flatfish, lionfish, mantis shrimp and sea snakes, amongst others, to deceive potential predators.
Not only does it change its colour patterns and shape, it also adopts a good impersonation of movement, such as the undulating swims along the seabed for the flatfish mimicry. The amazing thing about this behaviour, is that mimics have evolved a defence that relies on predators seeing them rather than not seeing them, unlike their relatives who use camouflage to hide.
Perhaps most intriguing, the mimic octopus presents what it considers the greatest threat to a potential predator. So when attacked by damselfish, it mimics the banded sea snake, a known predator of damselfish. But is such behaviour inherited or learned and how does it decide what to mimic? No one yet knows how mimic octopuses choose to perform one behaviour over another, and the full repertoire of models is still up for debate.
For example, the mantis shrimp mimicry may look like any old octopus sitting at its den entrance. The tunicate mimicry could fall under the definition of camouflage. But what we think doesn't matter, it's what the predators think, and none of this has been really tested To find out more about how such behaviour came out and how much it is learned, we can though study its evolution.
Evolution of a mimic
Scientists from the California Academy of Sciences used DNA analysis to look at how and why this intriguing ability evolved in an animal that usually relies on invisibility to avoid predators. Octopus are normally masters of camouflage, changing the colour of their skin through chromatophores, pigment-containing, light-reflecting cells found in amphibians, fish, reptiles, crustaceans, and octopus. Instead of blending in to avoid detection, the mimic gets out and actually shows itself in the most spectacular of ways
Using DNA sequencing to construct a genealogy of the mimic and 35 of its octopus relatives, the team were able to chart the order in which key mimic traits evolved. First, the mimic’s ancestors used bold brown and white colouration to shock predators when their camouflage was unsuccessful. Later ancestors then developed the swimming method used by flatfish and the longer arms to improve the mimicry.
The last evolutionary step was combining these abilities. The mimic, at the end of this evolutionary line, can display bold colouration and swim like a flatfish. It is a very risky shift in defence tactics. Somehow through natural selection, being conspicuous has allowed the mimic octopus to survive and reproduce more successfully than its less showy ancestors, and eventually evolve into its own lineage. Working out how they select what to mimic is more difficult.
Assessing just how much of this bizarre and unique behaviour is learned, is another challenge. Each octopus has a repertoire of shapes/body patterns it runs through- sometimes randomly, sometimes in a certain order. Other behaviours may be influenced by learning, or the situations the octopus encounters.
For example, one octopus is known to mimic the fish it forages with (social mimicry). Its possible that learning may influence mimicry and other behaviours that the octopus inherited from its ancestors.”
Smarter than we thought
It's clear that we're not dealing with your average invertebrate. Given all this, are octopuses intelligent in the vertebrate sense. Intelligence in all animals including humans is a thorny issue at the best of times. Like any animal, wild octopuses spend most of their time resting, looking for food, trying not to be eaten, and mating.
The way they accomplish these daily needs can involve interesting aspects of learning, memory, and choice. Some insects have far more complex mating behaviours; mantis shrimps have more complex vision and possibly communication. And some deep sea worms have more exceptional defences. All of these traits reflect thousands of years of natural trial and error played out in their ancestors- and all of this is pretty cool, whether or not it fits an academic definition of intelligence.
Octopuses present quite a conundrum to biologists. They are short-lived, unsociable invertebrates, the opposite of what we think has driven intelligent behaviour.
Yet science shows us that they are indeed smarter than your average invertebrate. Those of us who have had close encounters with these enigmatic creatures know that they are certainly a smarty pants; curious, crafty and some would say playful.
Perhaps even more sensational, are revelations are that not only do they engage in play, but that octopus also have personalities in the human sense. Discussions of animal personality are controversial and it is hard to measure and quantify. Personality is classed as “temperamental differences” between individuals within a species.
In humans, for instance, life in an ever-changing environment with numerous threats requires a large variety of response and therefore the evolution of different temperaments or “personalities”.In the wild, we definitely see evidence that some octopuses have different ways of behaving than others. Call it personality if you like, this variation in behaviour has serious implications for how octopuses mate, find food, and keep them from being eaten.
Intelligent? well that all depends on how you define intelligence, complex yes, successful in their world? yes certainly. Science is challenging our expectations of animal behaviour, especially in invertebrates. Octopus play key roles in marine ecosystems, are biologically and behaviourally fascinating and have enormous potential for discovery.