Good mimics have the costumes and the acting skills

There are lots of ways to fool an observer, and I mentioned quite a few in my post on the Cafe Scientifique talk that I gave in September. However, one aspect that I didn’t mention there was “behavioural mimicry” – where an animal acts like another animal in order to fool a potential predator or prey.  This sort of behaviour has been reported plenty of times in the field, but has never been studied in a systematic way. My collaborators over at Carleton (led by Tom Sherratt and Heather Penney, who collected the data as part of her MSc thesis work) and I have just published a paper (press release here) which provides just such an overview, and tests a few key evolutionary hypotheses along the way.

First, though, what does behavioural mimicry look like?  In the system that we studied, hover flies (which can’t sting) have evolved to look like wasps and bees (which can sting). The theory is that birds learn to associate the characteristic yellow and black patterns of wasps with a nasty sting and so leave yellow and black insects alone.  Hover flies have exploited this and so get eaten less even though they don’t have any form of defence. Here are a few photos (taken by Heather Penney and which I mentioned in an earlier post on imperfect mimics):Small hoverfly mimicry gallery

These pictures show clearly the variation in similarity between a stinging wasp and three harmless hover flies. However, only now do we have similar data on the similarity of behaviours between these two groups.  We show that behavioural mimicry is actually relatively rare.  Out of 59 species of hover flies, only 6 showed behaviours that looked like wasp behaviours, and those 6 species were restricted to just two genera of hover flies (Temnostoma and Spilomyia).  What is most interesting, though, is that these two genera of hover flies are two of the most similar in terms of appearance as well, and we didn’t find any examples of hover flies that don’t look much like wasps but that do show wasp-like behaviour.  If you look carefully at the following videos (both by Henri Goulet), you will see examples of the following behaviours: “mock-stinging” (pressing the tip of the abdomen against a surface as if stinging), “wing-wagging” (movement of the wings like a wasp – hard to describe but watch the videos!), and “leg-waving” (waving dark front legs in front of the head to imitate the longer antennae of a wasp). First, Spilomyia longicornis (the same species illustrated as a “good mimic” above):

…and another species in the same genus, Spilomyia fusca:

So what does this all mean? Well we can pull out a few key messages:

  1. Behavioural mimicry is relatively rare, even in a group like the hover flies which is quite well known for this sort of mimicry.  Furthermore, those species that do show behavioural mimicry are closely related, suggesting a small number of evolutionary origins.
  2. It appears that only those species that have evolved shape and colour like wasps have evolved behaviours like wasps.  This suggests that whatever evolutionary pressures drive the evolution of morphological similarity also drive the evolution of behavioural similarity.

This was a really interesting paper, quantifying for the first time just where and how often this fascinating behaviour arises. There are lots more questions, though: how effective is this behavioural mimicry in deterring predators? Is there really no benefit to behavioural mimicry if you don’t already look like a wasp? How common is behavioural mimicry in other celebrated groups of mimics like ant-mimicking spiders? As ever, lots more interesting research to be done!

If you have any questions about the paper, I’d be happy to answer them in the comments.

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