Acoustic Mimicry in Anti-predator Paradigm

A mimicry system can be defined as an ecological arrangement whereby organisms execute specific roles in relation to one another (Wickler, 1965).  In order to qualify as a mimicry system, an organism needs to fulfill the role of the model, who is capable of producing a perceptible stimuli.  Another organism, the mimic, copies this stimulus in order to gain fitness at the expense of yet another organism, the dupe.  The dupe, who is receptive to the model's stimuli, is thus deceived by the mimic's imitation (Pasteur, 1972).  Typically, the model and mimic are prey items of the dupe that manage to avoid predation.  A beautiful example of this system can be found in the interactions between echolocating bats and arctiid moths.


The night sky is sated with a multitude of anti-predator interactions between insectivorous echolocating bats and their nocturnal prey who have orchestrated an ancient predator-prey arms race for thousands of years. The night predator's ultrasonic sonar has exerted great selective pressure on insects to develop methods of detection and evasion.  Many moth species, for example, have developed highly sensitive ears capable of detecting the ultrasonic frequencies (above 20 KHz) of sympatric bat cries. In addition to developing ears for predator detection, tiger moths of the Lepidopteran family Arctiidae display a rather impressive array of chemical, morphological, and behavioral defenses against their vertebrate and invertebrate predators.  Escalating the evolutionary arms race against one of its most dangerous predators, some arctiid moths have developed a remarkable chemical defense, which renders them noxious and unprofitable to bats. Tropical arctiids in particular display a wide range of toxicity, a feature that could have led to the evolution of a variety of amazing mimics species (Blest 1964).

Predator-prey interaction between bat and moth captured with high-speed infrared camera (Credit: Image courtesy of Wake Forest University; Hristov and Conner, 2005)


Here, we focus on one of the more striking instances of mimicry, that of acoustic mimicry in the bat-moth predator-prey paradigm.  During the course of evolution, a few tiger moth species who already possessed bat detecting ears and powerful chemical defenses, evolved the ability to produce trains of ultrasonic clicks in response to the echolocating cries of bats. These clicks seem to serve an aposematic function, that is to say, appear to warn bats of underlying chemical defense and unprofitability.  Click here to see a footage of the noxious and sound-producing tiger moth Cycnia tenera  being avoided by a red bat (Barber and Conner, 2007).

Over the course of evolutionary time, other chemically defended tiger moths begin to mimic the model by themselves producing ultrasonic warning signals, this is a case of Mullerian mimicry as the moths still retain the chemical defense that makes them unprofitable prey.  Still other species that lack chemical defense, and are therefore quite palatable to bats, begin to mimic the model as well.  Here we are dealing with a case of Batesian mimicry as the moths producing the ultrasonic clicks are effectively fooling the bats into believing that they possess a non-existent toxicity.  


model moth

The model and the mimics. Noxious Cycnia tenera (Left) who is imitated by the noxious Mullerian mimic, Syntomeida epilais (Center) and the palatable Batesian mimic, Euchaetes egle (Right).


We present the acoustic mimicry system exemplified by echolocating bats and arctiid moths under the umbrella of Tinbergen's four areas of biology: phylogeny, ontogeny, mechanism and adaptation (See figure below for a more detailed explanation).


“There is, of course, overlap between the fields covered by these questions, yet I believe with Huxley that it is useful both to distinguish between them and to insist that a comprehensive, coherent science of Ethology has to give equal attention to each of them and to their integration.”

---Niko Tinbergen


Tinbergen's four questions

Image courtesy: Suzy Renn’s B342 :Animal Behavior course website