Wednesday, February 18, 2009

And it's not just the gammas...

(Sorry for all the insectoid posts; Science just seems to have the most interesting articles on our six-legged friends lately!)

It's not just gamma male beetles that benefit from fake-outs. According to an article by Barbero et al., some species of butterfly also benefit from mimicry--of ants, of all things.

Ant society is very complex; most species include a number of different "genders" and societal roles, all of which are rigidly defined. (Emancipation has not yet come to the ant world.) Certain castes of ants are more valuable, and therefore more highly protected, than others. The extreme of this is, of course, the queen, who receives the most care and attention.

Although most of the communication necessary to keeping such a complex society running is chemical (e.g., pheromones) and physical (i.e., physical contact), apparently some of it is acoustic. Adults in certain ant subfamilies can produce "stridulations" (which I assume sound something like scraping noises, although I could be wrong) to communicate. Within these subfamilies, different castes produce different sounds (and larvae and pupae produce no sounds at all).

A number of ant species are also parasitized by the larvae and pupae of other insects. Barbero et al focused specifically on the butterfly species Maculinea rebeli, which parasitizes the ant species Myrmica schencki. M. rebeli larvae and pupae can infiltrate M. schencki nests and fool the ant workers into taking care of them. A significant characteristic enabling the butterfly caterpillars to survive in the ant nest is their ability to produce chemicals that mimic the chemicals produced by the ant larvae.

However, M. rebeli larvae and pupae apparently show higher "social status" than would be expected simply from the chemical mimicry. For example, M. schencki workers will rescue M. rebeli larvae and pupae instead of "dummies" that have been painted with the same chemical mimics. In addition, M. schencki queens will sometimes treat the butterfly larvae and pupae as rivals; at the same time, the ant workers treat the butterfly larvae like queens. This discrepancy led Barbero et al to guess that perhaps the butterfly larvae and pupae are able to produce acoustic signals that increase their status in the ants' social heirarchy.

As it turns out, they may be right. M. schencki workers and queens do produce distinct stridulations (i.e., they sound different to the other ants), and M. rebeli larvae and pupae produce sounds that are more similar to the queen ant sounds than to the worker ant sounds.

To test their hypothesis, Barbero et al carried out a number of tests. First, they recorded the sounds produced by the ant workers and queens. They played those sounds to "naive" worker ants. (They also exposed control groups to white noise and to silent speakers.) The worker ants showed more interest in the ant noises than the white noise or the silent speakers. In addition, the noises from the queens caused the workers to become more alert and to assume postures that are associated with "serving" the queens. This test confirmed that worker ants do respond to acoustic signals from other ants.

Next, the researchers recorded sounds from butterfly larvae and pupae. They played those sounds to similarly "naive" worker ants. The ants responded to both larval and pupal calls in the same way they responded to the queen ant calls.

Based on their observations, Barbero et al conclude that M. rebeli larvae and pupae are first able to enter an M. schencki nest through chemical mimicry. Once they are inside, however, acoustic mimicry may also play an important role in preventing the ants from rejecting them.

Barbero, Francesca, Jeremy A. Thomas, Simona Bonelli, Emilio Balletto, and Karsten Schönrogge, 2009. "Queen ants make distinctive sounds that are mimicked by a butterfly social parasite." Science 323: 782-785. doi: 10.1126/science.1163583

1 comment:

Cyn Hatch said...

Hey Kate, it's Cyn Hatch (ex W&N), my prev. employer (Kent) is looking for middle-school science writers. Drop me a line at