The work was done with 29 young common cuttlefish, sepia officinalis, around 5cm long, compared with (the Wikipedia) full size of around 50cm. But not so small compared with the size of their tanks, at 10cm diameter. While my recollection of the cuttlebones on beaches is that they are mostly around 15cm in length. No discussion of these matters in the present paper.
The work was done in three phases: preparation, experiment 1 and experiment 2. These three phases are sketched below.
Preparatory
Demonstrate that these cuttlefish have a clear preference for shrimp over crab. During which demonstration, the cuttlefish seem to be getting a lot more to eat than they get during the experiments.
We are told very little about this part of the work, which might have been interesting in its own right.
Experiment 1
Condition 1: crab available every day, shrimp available every night.
Condition 2: crab available every day, shrimp available on random nights.
The results suggest that the cuttlefish quickly learn to lay off the crab when regular shrimp is available later.
Experiment 2
Crab available every day. Shrimp available every other night.
The results suggest that cuttlefish learn to lay off the crab on days when shrimp follows later.
Comment
Again according to Wikipedia, these cuttlefish are mainly nocturnal feeders in the wild. Which makes the experimental conditions reasonably unnatural – not that this disturbs the conclusions, which are more about neural capabilities than habits in the wild.
Data is available as an Excel workbook; quite small with just a few hundred data cells, all taking integer values between 0 and 2. I thought it rather poorly presented.
Statistics are presented with rather more precision than is appropriate. I thought the presentation of the two figures could have been improved and that there might usefully have been more figures, perhaps the odd table – but perhaps there are rules about how many figures and tables are allowed.
It seems reasonably clear that cuttlefish do have preferences which are reflected in their feeding behaviour. In particular, they will not take crab when shrimp are expected. Behaviour which requires memory and impulse control – that is to say the cuttlefish does not make a grab for anything vaguely suitable that comes within range. I imagine that lots of other animals display similarly intelligent behaviour – with the interest here perhaps being, as the authors note, that cuttlefish diverged from us vertebrates more than five hundred million years ago. Very different lineages.
On impulse control, one possibility which occurs to me is the hungry tiger on the way to the waterhole to lie in wait for deer coming to drink in the evening. Does the tiger on the way tend to ignore any prey he comes across, its focus being the upcoming water hole?
Both this paper and Bing suggest that a lot work has been done on the feeding habits of cuttlefish. Perhaps they are convenient experimental animals. One paper (reference 4), not among the references to the present paper, although its authors are, demonstrates that a preference for crabs can be established by just showing crabs to cuttlefish embryos – a result which, if confirmed, needs to be taken into any model of the present preference for shrimps.
Systems
I imagine that one could model what the cuttlefish brain was doing, needs to do here, at the level of system design rather than at the level of neurons, but I found the discussion along these lines rather high flown and I offer the system following – a system only loosely connected with what cuttlefish actually do, but which might serve as a vehicle for productive discussion.
We suppose that the crabs and shrimps that our cuttlefish comes across are all of a suitable size to be prey. Nothing so big as to be awkward to eat or dangerous to attack. We also suppose that our cuttlefish is a good hunter and always gets what he goes for.
We suppose that our cuttlefish has a preference for shrimp.
We suppose that our cuttlefish likes to eat once in each twenty four hour period. Then, once he has eaten, he goes to sleep for the remainder of the period.
Sub-system 1
Scanning the world, looking for prey.
If a shrimp appears, he eats it.
If a crab appears, he does a sum: X = A × B. Where A is the probability of a shrimp appearing in the remainder of the current period and B is the relative preference for shrimp. If X > 1, then the cuttlefish waits. Otherwise he goes for the crab.
Sub-system 2
Maintaining the probability, the chance that a shrimp will appear in the remainder of the current period.
Option 1: keep a count of shrimps seen by day. Compute the proportion of days in which a shrimp was seen over the past N days, where N is some integer constant. Set A equal to that proportion.
Option 2: keep a first count of shrimps seen during the first half of the day and a second count of the shrimps seen during the second half of the day. Compute the two proportions, P1 and P2. In the first half of the day set A to P1 + P2. In the second half of the day set A to P2.
Option 2 is better than option 1, and would cope with the first experiment. And one could go further along these lines - but they would not cope with the second experiment, for which the probability calculation needs to allow for days not being all alike.
Option 3: keep proportions for each of M sorts of days, where M is some small integer constant. Have another sub-system which maintains a guess at what sort of day it is. Otherwise, proceed as before.
Lots of possibilities!
Conclusions
This paper was in a Royal Society journal called ‘Biology Letters’, presumably intended for short communications. Nevertheless, I was expecting rather more.
That said, this story of brainy cuttlefish certainly caught the attention of the media, no doubt helped by the accessibility of the results, of the story.
For their size, cuttlefish are considered to be quite brainy animals, with complex nervous systems. Perhaps this and their strangeness gives them their appeal. Perhaps cuttlefish are known to be a good sell, along with octopuses.
References
Reference 1: Cuttlefish show flexible and future-dependent foraging cognition - Pauline Billard, Alexandra K. Schnell, Nicola S. Clayton and Christelle Jozet-Alves – 2020.
Reference 2: https://www.sciencedaily.com/releases/2020/02/200208094304.htm.
Reference 3: https://www.dailymail.co.uk/sciencetech/article-7965751/Clever-cuttlefish-resist-filling-crab-lunch-know-theres-shrimp-dinner.html.
Reference 4: Embryonic visual learning in the cuttlefish, sepia officinalis – Darmaillacq A, Lesimple C, Dickel L – 2008.
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