The Evolution of Colonial Insects

Figure 1 - Ants as a superorganism.

The transition from solitary to eusocial organisms has been likened to the transition from unicellular to multicellular life, that multicellularity and sociality represent two major and analogous evolutionary innovations. Both being examples of how individual elements, that is cells and individuals, can cooperate to enhance evolutionary fitness. This has led to eusocial insects being dubbed by some as 'superorganisms' (Figure 1).

The 'superorganism hypothesis' (Wilson, 1989) considers eusocial colonies as biological individuals because they act as a single, cohesive unit. That is, they are individuated and persist over time i.e. once colonies are formed they do not dissolve or merge with other colonies, (except in the case of some termites; Matasura and Nishida, 2001); they undergo development, as opposed to being formed by the aggregation of solitary insects; and most importantly, because of the reproductive division of labor, for some species the colony itself is the unit of reproduction (Wheeler, 1911). In this way, the society or insect colony becomes the extended phenotype of the collective genome of the society (Hölldobler and Wilson, 2005).

Another similar theory posits that there are economies of scale related to energy use such that cells in larger, more complex animals require less energy per capita. Eusocial species experience similar relationships with colony size, with evidence suggesting that these colonies are functionally organized and are using and expending energy for the basic processes of life in much the same way that individuals are (Hou et al., 2010).

While there is still contention as to the use of the term 'superorganism' (Boomsma and Gawne, 2018) and whether or not analysing these colonies as singular organisms is meaningful, the analogous transition from singular to eusocial with the evolution of multicellular life is undoubtedly an interesting phenomenon.


References:
Boomsma, J.J., Gawne, R., 2018, Superorganismality and caste differentiation as points of no return: how the major evolutionary transitions were lost in translation., Biological Reviews, 93, 28–54.

Hölldobler, B., Wilson, E., 2005, Eusociality: Origin and consequences., Proceedings of the National Academy of Sciences Sep 2005, 102 (38) 13367-13371; DOI: 10.1073/pnas.0505858102

Hou, C., Kaspari, M., Vander Zanden, H.B., Gillooly, J. F., 2010, Energetic basis of colonial living in social insects., Proceedings of the National Academy of Sciences of the United States of America, 107(8), 3634–3638. https://doi.org/10.1073/pnas.0908071107

Matsuura, K., Nishida, T., 2001, Colony fusion in a termite: What makes the society "open"?, Insectes Sociaux. 48. 378-383. 0.1007/PL00001795.

Wheeler, W. M., 1911, The ant-colony as an organism., J. Morphol. 22, 307–325. doi: 10.1002/jmor.1050220206

Wilson, D.S., Sober, E., 1989, Reviving the superorganism., J Theor Biol. 136:337–356


Figure:
The tiny and big, https://steemit.com/ants/@thegreatlife/the-tiny-and-big, 23/05/20