Chemical mimicry or crypsis—the evolutionary game played by parasitic ants invading other colonies

Abstract

Some ant species are specialised parasites that invade the nests of other ants and steal their food, larvae, and eggs. To be successful, they must evade detection by patrolling hosts who attack invaders. Ants distinguish invaders from individuals of their own nest through the cuticular hydrocarbon profile, as their nestmates have a similar mixture of coating chemicals. To circumvent this, some parasites adopt mimicry, using a mixture of chemicals that has a similar composition to that of their hosts, whilst others adopt crypsis, with a reduced amount of chemicals. Here, we develop a mathematical model to describe the conditions under which each of these strategies evolves, assuming that the parasites and hosts are ants with their own colonies. Host ants distinguish their nestmates from parasites through differences in their chemical traits, which are represented in multi-dimensional space. Parasitic ants engage in competition with other conspecific colonies, which is more intense between colonies with similar chemical traits, jeopardising the advantage of cryptic parasites. We then define parasites’ fitness with respect to chemical profiles and discuss the evolution of their chemical strategies. Cryptic parasites evolve when competition among colonies is weak, when many types of host colonies exist, and when host recognition accuracy is high. Mimetic parasites evolve under the opposite conditions.