Smarter cuttlefish show better self-control

It was early morning, and I could taste the ocean salt in the air as a warm fog had settled across Eel Pond at the Marine Biological Laboratory in Woods Hole, Massachusetts. I made my way to the indoor aquarium bearing my leopard-print gumboots to protect my socks from the wet aquarium floor. My efforts to stay dry were futile because moments later I walked under an unexpected cascade of saltwater that hit my legs and proceeded to run down to my socks resulting in a squelching sensation every time I took a step. The culprit was Franklin, a cranky common cuttlefish that had precipitously squirted water from her siphon just as I had passed by her open-air tank. Wet, cold, and annoyed, I glared down at her. She glared back, her pupils contracted to form two unearthly W-shapes, and she extended her 8 arms towards me, exposing her siphon as if in mock charge to squirt me again. “OK you win”, I say as I put my arms up to surrender “You can forgo experiments today”. I can’t help chuckling to myself as I leave to change my socks; Franklin has attitude, exquisite precision, and a knack for waiting for the exact moment to ensure she hits her target–me. 

Franklin does not always enjoy participating in experiments and this squirting defence tactic has become a frequent routine. The interesting thing is that Franklin never squirts me during my evening visits because this is when I provide her with dinner. Is she using self-control to adjust her behaviour in response to the context of my visits? Or has she simply learnt to associate my morning visits with an activity she doesn’t like? 

Squirting saltwater is not the only behaviour that could be optimized through self-control. Cuttlefish have been known to optimize their foraging behaviour through sophisticated learning and memory abilities. Specifically, they can quickly adjust their foraging behaviour in response to changing prey conditions and by learning and remembering patterns of food availability. Could cuttlefish also optimize their foraging behaviour by exerting self-control? Self-control is a cognitive feature defined as the ability to avoid temptation now to lead to a better outcome in the future. 

The shrimpy marshmallow test

To answer this question, I joined forces with researchers from both the University of Cambridge and the Marine Biological Laboratory including Professor Nicky Clayton FRS and Professor Roger Hanlon. We adapted the 1970’s Stanford Marshmallow test, which presented children, aged 3–5, with a choice of taking an immediate reward, a single marshmallow, or waiting for a better but delayed reward, two marshmallows. We presented cuttlefish with a similar dilemma. Specifically, they were presented with two desirable prey items, each within a separate Perspex chamber. One chamber was baited with a piece of king prawn, their second preference, which they could eat immediately. The other chamber was baited with a live grass shrimp, their first preference, but they could only eat the live shrimp if they waited and did not eat the piece of prawn. We tested a range of delays starting from 10 seconds and increasing the delay by increments of 10 seconds. All six cuttlefish waited for the better but delayed live shrimp and were able to tolerate delays for up to 50–130 seconds, which is comparable to what we see in long-lived social species such as chimpanzees, crows, and parrots. 

For long-lived social species, the benefits of advanced self-control are obvious–deny yourself now to have a longer and better life, and resist temptation to help a social partner in the present moment to receive reciprocated favours in the future. The same rules do not apply to cuttlefish as they are short-lived, with an average lifespan of two years, and are not social. So why would a fast-growing cuttlefish be a picky eater? Perhaps the advanced self-control we see in cuttlefish evolved as a by-product of selection on an unrelated trait – camouflage. During camouflage, cuttlefish stay motionless on the ocean floor for long periods of time to avoid detection from predators. This ‘sit-and-wait’ behaviour might have influenced the evolutionary expression of self-control in cuttlefish. 

Self-control – a cornerstone of intelligence

Self-control is a critically important building block for the evolution of complex decision-making and future planning because it requires an understanding that ‘less is sometimes more’ and that avoiding temptation might lead to a better future outcome. In humans and chimpanzees, individuals who perform better in tests of self-control also perform better in tests of general intelligence. We found a similar link in cuttlefish. 

We tested learning performance, an indicator of intelligence, in a separate reversal-learning task. Cuttlefish were tested by placing two markers that differed in colour in random locations in their tank. Subjects first had to associate one colour with a reward and then subsequently learned to associate a reward with the other colour. Individuals who were quicker at learning the first association and quicker to learn the reverse association were better at resisting temptation in the shrimpy marshmallow test. 

This is the first demonstration of a link between self-control and learning performance in an invertebrate and also outside of the primate lineage. Finding that cuttlefish are capable of some of the facets that are thought to be fundamental to the evolution of human intelligence is an extreme example of convergent evolution, where animals with completely different evolutionary histories possess the same cognitive feature. Demonstrating cognitive similarities across such diverse animals is an important piece of the evolutionary puzzle and brings us one step closer to pinpointing the origins of intelligence.