Social Parasitism : Blue Butterflies in Ant Colonies
Biology 342 Fall 2011
Ellen Levkoy & Rachel Strominger
Mechanism examines the proximate physiological basis for the performance a behavior .
Mechanism of semiochemical and sound production.
Vast, complex Myrmica colonies maintain cohesion largely through the exchange of distinctive semiochemicals (a generic term for some chemical mixture that conveys a message between organisms). Combined with other forms of communication, these allow Myrmica to recognize nestmates and detect intruders, as well as determine the caste of other Myrmica they encounter . Maculinea gain acceptance into the host Myrmica colonies by producing semiochemicals that closely mimic those of Myrmica larvae. In most studied populations, each regional Maculinea is host-specific to one primary Myrmica species, whose hyrdocrabon profile if specifically mimcs. Most species of Maculinea are predatory after entering the nest, but Maculinea is parasitic, using this chemical mimicry to prompt nurse ants to feed them by regurgitating food. Once in the nest, they adapt their chemical signals specifically to the particular host colony in which they find themselves. This is done through a combination of synthesis of new semiochemicals and acquiring of semiochemicals from their environment, although not much is understood about this second round of chemical camouflage [1, 2, 3].
Myrmica adults produce a chirping noise by stridulation--scraping a plectrum located on an anterior segment of the abdomen across a file on the first segment of the gaster (the last section of an insect's body). However, whereas Myrmica larvae are mute, M. rebeli larvae and pupae emit a sound resembling the alarm call of a Myrmica queen when they are stressed. The larvae do this with a very similar structure as the Myrmica, and the pupae do this with a tooth and comb structure. Producing this sounds causes the workers to stand guard over them. The real queens' chirps are recognized as different from other ants' (but not from M. rebeli) by the workers because her pars stridens is longer and she has a wider gap between the ridges of her file .
image: Stridulation organs of Myrmica queen and worker and Maculinea pupa and larva .
See http://www.sciencemag.org/content/suppl/2009/02/05/323.5915.782.DC1 for audio clips of stridulations.