Chemical Camouflage

A study published by Whitehead et al. (2014) discusses the ant-plant mutualism that occurs within some ecosystems. The plant provides ants with shelter and/or food, while the ants offer protection to the plant from other herbivores. Ants are extremely good at defensive mechanisms, protecting the plant against most herbivore attacks (Whitehead et al., 2014). Yet sometimes there are animals that can sneak past the ant defence system without the colony knowing. These organisms benefit greatly from flying under the radar as they have access to competition free food that is usually readily available for the ants (Whitehead et al., 2014). So how do they go undetected while essentially eating dinner at the same “restaurant”?

 Some examples of these defences are having a toughened exocuticle, shelter-building behaviours and behavioural avoidance maneuvres (Whitehead et al., 2014).  Yet the defence mechanism we are talking about today is chemical camouflage. Ant societies are known to use chemical cues to recognise individuals from the same colony and to transfer complex information (Jackson & Ratnieks, 2006). To do this they use cuticular hydrocarbons, which are also used for protection by the ant (Otte, Hilker & Geiselhardt, 2018). An organism using chemical camouflage can circumnavigate through a colony of ants without being detected by copying the ants cuticular hydrocarbon profile (Otte, Hilker & Geiselhardt, 2018). This means that the organism benefits from the plants or ant colony without being involved in the mutual relationship (Whitehead et al., 2014).

An example of an animal using chemical camouflage against ants is the genus of leaf-footed bugs (Piezogaster reclusus). They feed on the plant Neotropical bull-horn acacias (Vachellia collinsii), who have a mutual relationship with the ants (Pseudomyrmex spinicola; Whitehead et al., 2014). The ants feed on the acacia’s floral nectaries and Beltian bodies, which are multicellular structures that contains large amounts of proteins and lipids, that the ants feed to their larvae (Rickson, 1975). The Piezogaster reclusus are sap-feeding insects, with a primary diet of sap from the young leaves of the acacias (Whitehead et al., 2014). The leaves wilt causing damage to the floral nectaries and Beltian bodies, this is costly for both the ants and the plants.

Piezogaster reclusus

Interestingly, Whitehead et al. found that when Piezogaster reclusus is transferred from one acacia tree with an ant colony, to a different area the Piezogaster reclusus no longer has an efficient defence mechanism. Which Whitehead et al. hypothesise that the chemical camouflage is colony specific.

There are many more examples of chemical camouflage being used in the environment (including diet induced!) but unfortunately we don't have time for them in this post. 

References:

Brooker R., Munday P., Chivers D., & Jones G. (2015). You Are What You Eat: Diet-Induced Chemical Crypsis in a Coral-Feeding Reef Fish. Proceedings of the Royal Society of London B.

Jackson D., & Ratnieks F. (2006). Communication in Ants. Current Biology. 16(15). 570-574.

Otte T., Hilker M., & Geiselhardt S. (2018). Phenotypic Plasticity of Cuticular Hydrocarbon Profiles in Insects. Journal of Chemical Ecology. 44(3), 235-247.

Rickson F. (1975). The Ultrastructure of Acacia cornigera L. Beltian Body Tissue. American Journal of Botany. 62(9), 913-922.  

Whitehead S., Reid E., Sapp J., Poveda K., Royer A., Posto A., & Kessler A. (2014). A Specialist Herbivore Uses Chemical Camouflage to Overcome the Defenses of an Ant-Plant Mutualism. PLOS ONE. 9(7), 2-9.