The Evolution of Colonial Insects

Due to its relatively recent occurrence, the evolution of human social structure is fairly well understood thanks to the extensive documentation we have in the form of written records and other remnant artifacts. To see how human society evolved before this, we look further back to archeological records or even to extant tribal societies and other closely related primate societies and by doing so we can make a fairly accurate sequence for how we think our societies came about.

Figure 1 - cooperative sister leafcutter ants.

The colonial insects have no such recorded history. Perhaps due to the parallels with our own society it is easy to take for granted the amazing complexity seen in colonial insects, but the evolutionary pathways to reach these complex societies are far less understood.

This means that piecing together the evolutionary timeline is far more difficult, with comparatively little evidence to be found in the archeological records. How these complex societies came about must be inferred, generally by analyzing common traits between social insects and observed behaviors in living insects that have gregarious but non-colonial lives. Colonial insects with a hierarchical social structure have evolved many times in the arthropods, particularly in Hymenoptera (the ants, bees and wasps), as well as in Blattodea (the termites). Common eusocial behavioral characteristics include distinct castes of workers [Figure 1] with well defined divisions of labour, individuals that forgo reproduction (sometimes even sterile), the cooperative care of offspring and the overlap of generations (Wilson 1971).

The evolution of euocialality has presented an interesting conundrum to many an evolutionary biologist. Even Darwin (1859) in his seminal work remarked on the problem of understanding eusociality as 

"one special difficulty, which at first appeared to me insuperable, and actually fatal to the whole theory. I allude to the neuters or sterile females in insect communities: for these neuters often differ widely in instinct and in structure from both the males and fertile females, and yet, from being sterile, they cannot propagate their kind."

Many theories have been proposed for how such complex eusocial societies can arise from solitary organisms. In this blog I aim to explore these theories and discover the various evolutionary stages that were the precursors to true eusocial insect societies.

References:

Darwin, C. On the Origin of Species by Means of Natural Selection. London, UK: John Murray, 1859.

Wilson, E. O. The Insect Societies. Cambridge, MA: Belknap Press of Harvard University Press, 1971.

Figures:
Leafcutter ants, https://mresbec.files.wordpress.com/2012/12/leafcutterants.jpg, 10/03/20