The Evolution of Colonial Insects

Figure 1 - Evolution of chemical communication in insects.

While solitary insects do utilise some forms of communication, it is generally relegated to a sexual context and used to communicate the appropriateness of a partner, most prominently through sex pheromones (Wyatt 2014). However the evolution of group living necessitates a higher level of intragroup communication and nestmate recognition in order to maintain the stability and security of the colony.

Even though kin recognition is important for solitary insects to avoid inbreeding, for insects with brood care it becomes even more crucial so as to stop parents from expending energy feeding or protecting anothers' young. This is furthered in eusocial species where nestmate recognition is used to maintain the integrity of the community from potential invaders.

In extant eusocial insects nestmate recognition is typically communicated through the use of cuticular hydrocarbons (CHCs) which are exchanged continuously though allogrooming and trophallaxis (licking and mouth-to-mouth transfer, respectively). This constant exchange ensures a high CHC homogeneity throughout the colony meaning significant differences would be detected as foreign invaders (Martin et al 2009). This mode of communication though CHCs is thought to have evolved through the emitter-sender model (Figure 1) where benignly emitted chemicals were once used as basic cues and eventually reciprocated to form two way communication (Wyatt 2014).

In species with small colonies, nestmates may recoginise each other based off visual cues of the faces (Sheehan et al 2008) but practically all other social insects rely on colony-level CHC cues. The transition from kin to nestmate recognition is thought to be aided by environmentally induced variations in CHC composition (food, gut bacteria, nest composition) meaning that even related individuals may carry different recognition cues (d'Ettorre and Lepoir 2010).  These colony recognition cues are thought to be learned through repeated exposure as ants have been shown to exhibit reduced aggression to non-nestmates whose cues have been previously encountered (Leonhardt et al. 2007). 

Next week we'll cover one of the most crucial aspects of eusocial insect communication - queen signals, the complex and powerful pheromone cues that the queen uses to regulate the colony and control the division of labor; and try to understand their potential evolutionary origins.


References:

d’Ettorre, P., Lenoir, A., 2010, Nestmate recognition, L. Lach, C.L. Parr, K.L. Abbott (Eds.), Ant Ecology, Oxford University Press, Oxford, pp. 109-194

Leonhardt, S.D., Brandstaetter, A.S. & Kleineidam, C.J., 2007, Reformation process of the neuronal template for nestmate-recognition cues in the carpenter ant Camponotus floridanus . J Comp Physiol A 193, 993–1000, https://doi.org/10.1007/s00359-007-0252-8, 29/04/20

Martin, SJ, Helanterä, H., Drijfhout, FP., 2011, Is parasite pressure a driver of chemical cue diversity in ants?,  Proc. Biol. Sci., 278, pp. 496

Sheehan, E.A. Tibbetts, M.J., 2008,  Robust long-term social memories in a paper wasp, Curr. Biol. 18, pp. R851-R852

Wyatt, T.D., 2014, Pheromones and Animal Behavior: Chemical Signals and Signatures, Cambridge University Press, Cambridge 

Figure:
Proposed Stages in the Evolution of Chemical Communication in Insects, https://www.sciencedirect.com/science/article/pii/S0092867416300496#sec1, 29/04/20