Is the mimic octopus misnamed?

The mimic octopus has star power. It’s not the largest octopus, nor the most colourful, but it makes for the best television.

Star power lets you do things that others don’t get to do. Here, it allowed Roger Hanlon and colleagues publish... a natural history paper. Despite Nobel laureate Niko Tinbergen’s warning that contempt for observation is a lethal trait for any science, basic observational papers of natural history are unusual. There are a few exceptions, particularly for behaviours that are very rare and have not been observed before.

In 2001, Mark Norman and colleagues published a paper describing a species of octopus that was undescribed, but has since been named Thaumoctopus mimicus. The clip below is a good introduction of the behaviours that Norman and colleagues saw, and how they interpreted it. Norman and colleagues suggested that this octopus imitates other species, including flounders, lionfish, sea snakes, and possibly anemones and jellyfish.



The issue is that “mimicry” implies a whole heck of a lot more than just “resemblance.” “Mimicry” implies a function; that one species is the “original” and another “wannabe” species has “copied” it – usually over evolutionary time – and that the “wannabe” gains advantages from looking like the original. But how do you test whether similarity is mimicry or mere resemblance?

In this paper, Hanlon and colleagues’s aim is to gather evidence as to whether mimicry is actually going on. They report on what they saw during many hours of videorecording these octopuses in their natural habitat. They don’t do any experiments or manipulations. Perhaps because of this, there is a lot of interpretation and subjectivity in this paper (slightly ironic for a paper that complains that the case for mimicry has been “overrated”).

Hanlon and colleagues agree that the octopuses are doing some mimicking, particularly flounder. In this clip below (not by the authors), you can see the octopus and the fish it is supposed to be mimicking.



The main quantitative finding in this paper is that octopuses are staying still and camouflaging themselves immediately before and after flounder-like swimming. Hanlon and colleagues argue that moving in a flounder-like manner is a way for octopuses to move quickly across a bare, sandy landscape without being detected as an octopus. They also show that the duration of a swimming burst by the octopuses is similar in length to a swimming burst by the flounders – both 6 seconds on average – which certainly is in line with mimicry.

Yet the case for mimicry is still weak.

For instance, the authors note that these octopuses also swim in a more typical octopus fashion: jetting with the rear of the mantle (“head”) going first. But there is no comparison of “regular” swimming with flounder-like swimming, which would be useful. A major prediction of true mimicry would be that the octopuses’ behaviour should be sensitive to context. For instance, one might predict that “regular” swimming occurs mainly as an escape response triggered by some external stimuli, whereas flounder-like swimming occurs more during spontaneous foraging.

Next, the authors note that when swimming like a flounder, the mimic octopus often shows a colouration that is not very founder-like! The authors suggest that this species might actually be a “poor mimic,” and that another local unnamed octopus, the “blandopus,” looks more like the local flounders when it swims.

Further, surprisingly little is know about the local flounders. Even what species are present is unclear. This makes it difficult to know what advantage an octopus might gain from mimicking it. Are the flounders poisonous or distasteful?

Although all of this is cast in the context of predator avoidance, Hanlon and company recorded not one instance of anything killing an octopus in 189 hours of videotaped recordings. They did record aggressive interactions with fish and one with a stomatopod, and noted some octopuses were missing bits of their arms, however, so clearly not all is rosy for the octopuses in this habitat.

Hanlon and colleagues mention that they were not allowed to do any collection during this study. They might have been unable to carry out simple field experiments, too. If someone was able to carry out field experiments, however, they might be able to, say, present octopuses with models of potential predators. In the first video above, it is suggested that the mimic octopuses imitate sea snakes to deter potential fish predators. If so, it should be possible to elicit that specific response experimentally in response to fish but not other threats.

Another simple field experiment could be present some models to potential predators of octopuses swimming in “regular” mode versus those in “flounder” mode. Again, if true mimicry is going on, there should be more investigations or attacks of models by predators towards models in “regular” mode.

Clearly, this is a huge amount of research still to do on these wonderful animals.

References

ROGER T. HANLON, LOU-ANNE CONROY, JOHN W. FORSYTHE (2008). Mimicry and foraging behaviour of two tropical sand-flat octopus species off North Sulawesi, Indonesia Biological Journal of the Linnean Society, 93 (1), 23-38 DOI: 10.1111/j.1095-8312.2007.00948.x

Additional: The DOI for this article refuses to work. Here’s direct link to the abstract: http://www3.interscience.wiley.com/journal/119394156/abstract

Norman MD, Finn J, Treganza T. 2001. Dynamic mimicry in an Indo-Malayan octopus. Proc. R. Soc. Lond. B 268: 1755-1758. doi: 10.1098/rspb.2001.1708