Chemical mimicry in an incipient leaf-cutting ant social parasite

Abstract

Some social parasites of insect societies are known to use brute force when usurping a host colony, but most use more subtle forms of chemical cheating either by expressing as few recognition cues as possible to avoid being recognized or by producing similar recognition cues to the host to achieve positive discrimination. The former "chemical insignificance" strategy represents a more general adaptive syndrome than the latter "chemical mimicry" strategy and is expected to be characteristic of early evolutionary stages of social parasitism. We tested this hypothesis by experimentally analyzing the efficiency by which Acromyrmex echinatior leaf-cutting ants recognize intruding workers of the incipient social parasite Acromyrmex insinuator. The results were consistent with the parasite being "chemically insignificant" and not with the "chemical mimicry" hypothesis. Gas chromatography-mass spectrometry analysis of cuticular hydrocarbon profiles showed that social parasite workers produce significantly fewer hydrocarbons overall and that their typical profiles have very low amounts of hydrocarbons in the "normal" C29-C35 range but large quantities of unusually heavy C43-C45 hydrocarbons. This suggests that the C29-C35

The origin of the chemical profiles of fungal symbionts and their significance for nestmate recognition in Acromyrmex leaf-cutting ants

“…Although the authors did not state this, the data clearly suggest that the fungus produces several classes of compounds that the ants do not synthesize. A recent study of A. echinatior workers from the same Panamanian population has confirmed this hypothesis by showing that ant workers had only alkanes, alkenes, and methyl alkanes on their cuticles (Lambardi et al 2007). This indicates that the aldehydes, methyl esters, and amides, which appear to covary with genetic differences between fungal symbionts (Table 2; Fig.…”

“…The current data do not allow us to assess whether the alkanes, expressed by both the ants and their fungi, are primarily ant-derived or fungus-derived. The most parsimonious hypothesis would be that the compounds expressed on the ant cuticle are ultimately determined by what the ants eat (i.e., by the total chemical blend of their fungal food), but proximately by ant speciesspecific biosynthetic pathways, so that only alkanes, alkenes, and methyl alkanes are expressed (Lambardi et al 2007). If so, these simple hydrocarbons would likely be transferred back to the fungus garden, which would explain why their relative quantities do not correlate with the genetic differences among the strains of symbionts.…”

The influence of slavemaking lifestyle, caste and sex on chemical profiles in Temnothorax ants: insights into the evolution of cuticular hydrocarbons

“…They can chemically mimic even hosts from a different order, such as ant-mimicking lycaenid butterflies or spiders [58,59]. Our focal slavemakers do not employ mimicry, but exhibit profiles distinct from their hosts, as has been reported for other social parasites [60][61][62] and as evident by the aggressive responses of their hosts [40,45,63]. Here T. pilagens is an exception, which can raid undetected by its hosts, presumably using chemical camouflage during raids [41].…”

Divergence in Cuticular Chemical Signatures between Isolated Populations of an Intraspecific Social Parasite

“…However, these compounds might also increase for other functions, which might explain why they were relatively abundant in the signature of intraspecific social parasites. In the socially parasitic A. insinuator ants, for example, the abundance of unusually long-chained hydrocarbons (n-alkenes) "might help to hide the information from the shorter hydrocarbons" or might serve as appeasing substances (Lambardi et al, 2007). Intraspecific social parasites might hide their identity in similar ways.…”