I was imitating Jean Chrétien a while ago to tell an anecdote to one of my students.
I could have done the greatest, most perfect, most spot-on, hysterical impersonation of Chrétien ever.* It all would have been lost on this student. An American undergraduate would be unlikely to recognize a Canadian prime minister, no matter how distinctive his speaking style was. (And it was. Oh, how it was.)
That’s the problem with imitation: it only works if both parties recognize what’s being imitated.
There’s imitation in the natural world, too, although it’s better known as mimicry. Almost everyone knows the example of the viceroy butterfly: tastes fine, but looks like the monarch butterfly, which tastes awful, so birds leave both alone because they can’t tell them apart. Thus, the viceroy gains an advantage. This is Batesian mimicry, named after Henry Bates. (Sean Carroll has a great bio of Bates in his book Into the Jungle.)
What if the viceroy butterfly and the monarch butterfly never met? Imagine that there was no overlap in their distributions at all? Now that would be a puzzle.
Those two butterflies do overlap, but a new review paper by Pfennig and Mullen argues that there are many cases where a mimic species occurs where the species its imitating does not. There are no cases where the mimic is completely isolated from the species it is mimicking, but the range of the mimic is often much greater than those of of the species being mimicked.
Pfennig and Mullen give examples of mimicking snakes that occur hundreds of kilometers away from the range of the model species. For the most part, there are only able to give crude estimates of how often the mimic is found without the model: basically, at this point, we’re unable to say little more than, “It happens.”
The paper lists several ways that we might be able to explain these distributions.
The first possibility is that mimicry really isn’t Batesian mimicry. For example, a species thought to be harmless might turn out not to be harmless (Müllerian mimicry). Alternately, both species have hit upon some sort of signal independently that predators avoid (convergent evolution).
Second, distributions of species are very dynamic. Just because the two species don’t overlap in some location now doesn’t mean that they have never done so. I like this idea, because it reminds us that things have a history.
Third, they discuss the possibility of hybridization leading to expansion for genes related to mimicry into new populations. Hybridization seems to occur quite a bit in butterflies, which are important models for mimcry, but this may not happen much in other species.
Fourth, the authors note that if a mimic is rare in arts of its ranges away from the model, it may not incur much of a cost, because many predators avoid feeding on unfamiliar foods. If anything, this paper underestimate the role that the predators could play in establishing the mimicking situation. If a long-lived, fairly smart predator feeds on the distasteful model at site A, it may remember that even if it encounters the mimic at site B very much later.
This review paper is a nice example of a review that tries to push the state of the art forward, and not just summarize.
Pfennig, D., & Mullen, S. (2010). Mimics without models: causes and consequences of allopatry in Batesian mimicry complexes Proceedings of the Royal Society B: Biological Sciences. DOI: 10.1098/rspb.2010.0586
Photo by ~K~ on Flickr, used under a Creative Commons license.
* It wasn’t, but it could have been. Work with me here.